The yolk sac is not clearly visible, 1.1 mm. Development and functions

Content

When conducting an ultrasound examination, the doctor should pay attention to the presence ovum, yolk sac and the size of the embryonic pole (the distance between the points of the embryo that are most distant from each other). The yolk sac can be seen before the embryo is visualized. The presence of this temporary organ confirms pregnancy.

Formation and functions of the yolk sac

The yolk (gestational) sac is a round sac that is attached to the embryo in the abdominal area. Inside there is a supply of nutrients necessary for the fertilized egg during its placentation. The embryonic organ is located in the chorionic space (between the chorion and amnion).

The gestational sac is formed already at the 2nd week of embryo development from the inner germ layer, which is called the endoderm.

The fetus needs a pouch almost until the end of the first trimester, until the organs of the unborn child begin to function.

Experts distinguish 3 stages of pouch development. He can be:

• primary, formed in the 2nd embryonic week, looks like a vesicle;
• secondary, after active cell division, a new cavity is formed from the primary, which is distinguished by the presence of two-layer walls;
• final, formed at 4 weeks, during the period when the formation of internal organs occurs.

Part of the education is included in digestive system embryo, and the remaining part is the formed yolk sac.

A formed organ is necessary for:

• providing nutrition to the embryo in the early stages of development;
• performing the function of the primary circulatory system;
• formation of blood cells;
• formation of the first fetal vessels through which nutrients are transported;
• delivery of oxygen to tissues;
• removal of metabolism.

All nutrients enter the embryo through the vitelline duct. Blood enters the walls of the sac through the primitive aorta. It circulates through a wide capillary network and returns to the tubular heart of the embryo through the vitelline vein. Thanks to the functioning of such a system, breathing and nutrition are ensured.

Corpus luteum on ultrasound

After the egg is released from the ovary, a corpus luteum is formed in the place where the follicle was. Luteinizing hormone is responsible for its development. It is this formation that secretes progesterone, the main hormone of pregnancy.

The corpus luteum is a temporary gland that appears after ovulation and, in the absence of pregnancy, decreases by the time menstruation begins. If the egg is fertilized and implanted, the corpus luteum continues to produce progesterone. The temporary gland remains active until the end of the 1st trimester.

The quality and size of the corpus luteum determines whether a fertilized egg can penetrate the endometrium. It also affects the development and growth of the fertilized egg.

When performing an ultrasound, the doctor can determine the size of the gland. It looks like a round sac with a heterogeneous structure, located on one side and slightly raised above the surface of the ovary.

If during the examination the temporary gland in the ovary is not visible, but the fact of pregnancy is established, then this is considered a bad diagnostic sign. With a small size of the corpus luteum, there is a possibility of developing progesterone deficiency.

Normal sizes by week

When performing an ultrasound scan in the first trimester, the doctor determines not only the size of the fertilized egg and embryo. The specialist also looks at the size of the yolk sac and corpus luteum.

The normal size of the corpus luteum during pregnancy is considered to be 19-29 mm. In the absence of problems, the value does not change significantly, remaining the same during the first 12 weeks. By the end of the first trimester, the size decreases. This is due to the fact that the functions of producing progesterone and maintaining normal hormonal levels during pregnancy are transferred to the placenta.

The size of the yolk sac depends on the period:

• 5-6 weeks - 2.2-3.5 mm;
• 7 week - 3.0-4.7 mm;
• 8 week - 3.9-5.5 mm;
• 9-10 weeks - 4.6-6.0 mm;
• 11 week - 4.2-5.9 mm;
• 12 week - 3.5-4.9 mm.

Minor deviations from the norm are not pathological.

At the end of the first trimester, it begins to decrease, its functions are transferred to the placenta.

Pathologies

During an ultrasound scan, the doctor can detect abnormalities. The moment when the gestational sac is not visualized should be alarming. Importance is also given to the size of this nutritional organ.

Pay attention to the formation of cysts of the yolk sac and corpus luteum.

Lack of visualization

Normally, from 6 to 12 weeks of pregnancy, the nutrient sac should be clearly visible on ultrasound. If it is not visualized during the indicated weeks of pregnancy, then this is an unfavorable diagnostic sign.

Early resorption of the yolk sac leads to the fact that the embryo ceases to fully receive the substances necessary for its development. This disrupts the production of hormones and essential enzymes. The process of producing red blood cells stops. When the yolk sac is reduced before the scheduled time, a miscarriage occurs. It is impossible to stop spontaneous abortion with medication.

If an ultrasound does not detect a heartbeat and there is no yolk sac, this indicates a regressing pregnancy. In such a situation, curettage of the uterine cavity is performed.

Small and large size

In some women, diagnostic tests reveal that the size of the gestational sac does not correspond to the established norm. If the formation decreases, it is suspected that the process of its resorption has begun. In this case, the death of the embryo is possible.

If the gestational sac according to ultrasound results more than normal, then there is no cause for concern. This situation is possible in cases where the estimated gestational age is incorrectly determined. This is possible with irregular menstruation. In such cases, the physician should determine the period in accordance with the size of the fetus.

Deviations in the size of the gestational sac have diagnostic value only in combination with other indicators. If the embryo is visualized in the fertilized egg, which is located in the uterine cavity, and the heartbeat is detected, then there is no cause for concern. An increase in value is considered individual feature.

Cyst

By the beginning of the 2nd trimester, the gestational sac resolves. Normally, it leaves a small cystic formation located at the base of the umbilical cord. In some cases, true cysts are formed from elements of the vitelline duct. Such cysts can only be detected after birth. They have a visible capsule, and they grow up to 1 cm in diameter. Cysts form near the child’s body.

When performing an ultrasound scan, the doctor can detect a corpus luteum cyst in the ovary. The reasons for their formation have not been established. Cysts do not affect the development of the fetus in any way, so there is no need to worry. In most women, the corpus luteum cyst resolves on its own by the end of pregnancy. When examined after childbirth by ultrasound, the condition of the ovaries does not differ from the norm.

When conducting the very first ultrasound examination, which is done when menstruation is delayed and in order to accurately diagnose the presence of intrauterine pregnancy, the fertilized egg can be examined. It is when the doctor sees this miniature formation on the monitor that he already informs the woman that she will soon become a mother. On the monitor you can see the fertilized egg, which is a small oval-shaped formation. In the early stages, the embryo, which will subsequently develop and grow in the fertilized egg, is not yet visualized, but soon it will grow up, and then it will be possible to clearly see it.

An empty fertilized sac is an egg without an embryo when pregnancy does not develop. The embryo is often visible already from the fifth week of pregnancy, but sometimes there are cases when even at this stage the doctor does not ultrasound examination does not see the embryo, in such a situation a repeat ultrasound is prescribed. Very often, a repeat ultrasound shows both the embryo and its heartbeat. When the embryo is not visible after six to seven weeks, then, unfortunately, there is a high risk that the pregnancy will not develop. In this article we will look at the norms of the fertilized egg by week.

What is a fertilized egg

The fertilized egg consists of embryonic membranes and an embryo. This period of pregnancy is its first stage of development. And it all starts with the fusion of two cells – male and female.

Then the fertilized egg actively begins to divide, first into two parts, then into four, and so on. The number of cells, like the size of the fetus, is constantly growing. And the entire group of cells that continue the division process moves along the fallopian tube to the zone of its implantation. This group of cells is the fertilized egg.

Having reached its goal, the fertilized egg attaches to one of the walls of the woman’s uterus. This occurs a week after fertilization. Until this time, the fertilized egg receives nutrients from the egg itself.

• Fertilized egg 2 weeks after insertion into the uterine cavity, it nourishes the swollen mucous membrane of this reproductive organ, which is already prepared for the process of development and nutrition of the fetus until the time of formation of the placenta.
• Children's place, or placenta, is created from the outer membrane ovum at 3 weeks, which at this time is already densely covered with villi. These villi at the site of attachment of the fertilized egg destroy a small area of ​​the uterine mucosa, as well as the vascular walls. Then they fill it with blood and immerse it in the prepared area.
• In general, the fertilized egg is the very first sign of a normally ongoing pregnancy. It can be examined by ultrasound after two weeks of missed menstruation. Usually in this case it is visible fertilized egg 3-4 weeks. The embryo becomes noticeable only at the 5th week of pregnancy. However, if the doctor diagnoses the absence of an embryo in fertilized egg 5 weeks- in other words, an empty fertilized egg, then the ultrasound is repeated again after a couple of weeks.
• Usually in this situation, at 6-7 weeks, the fetus and its heartbeat begin to be visualized. When fertilized egg at 7 weeks is still empty, this indicates a non-developing pregnancy. In addition to this complication, others may appear in the early stages of pregnancy - incorrect location of the fertilized egg, its irregular shape, detachments, and others.
• It is for this reason that it is important to go through ultrasound examination as early as possible so that the situation can be changed if it can be corrected. Since in the first trimester ( fertilized egg up to 10 weeks) there is a high probability of spontaneous miscarriage, detachment and other pathologies. However, enough about the sad things.

Fertilized egg at 6 weeks and before this stage of pregnancy has oval shape. And an ultrasound examination usually evaluates its internal diameter - the SVD of the fetal egg. Because ovum size 7 weeks or at another stage of pregnancy is a variable value, that is, the error in identifying the gestational age using this fetometric indicator.

On average, this error is 10 days. Gestational age is usually determined not only by this indicator, but also by the values ​​of the coccygeal-parietal size of the fetus and other indicators, which are also very important

Diameter of fertilized egg by week

When the fertilized egg has a diameter of 4 millimeters, this indicates a fairly short period of time - up to six weeks.

• Often they are fertilized egg size 4 weeks. Already at five weeks, the SVD reaches 6 millimeters, and at five weeks and three days the fertilized egg has a diameter of 7 millimeters.
• At the sixth week, the gestational sac usually grows to eleven to eighteen millimeters, and the average internal size of the gestational sac of sixteen millimeters corresponds to a period of six weeks and five days. At the seventh week of pregnancy, the diameter ranges from nineteen to twenty-six millimeters.
• Fertilized egg at 8 weeks increases to twenty-seven to thirty-four millimeters. At this stage, the fetus can be clearly seen on ultrasound.
• Fertilized egg 9 weeks grows to thirty-five to forty-three millimeters.
• And at the end of the tenth week, the fertilized egg measures about fifty millimeters in diameter.

As you can see, fertilized egg at 4 weeks It differs very much in size during the tenth week.

The question of how quickly the fertilized egg grows can be answered with confidence: until the fifteenth to sixteenth week, its size increases by one millimeter every day. Further, the diameter of the fertilized egg becomes larger by two to three millimeters per day.

Average size of the fertilized egg in the first trimester of pregnancy

Date of last menstruation (weeks)	Time at conception (weeks)	Inner diameter (mm)	Area (mm 2)	Volume (mm 3)
5	3	18	245	2187
6	4	22	363	3993
7	5	24	432	6912
8	6	30	675	13490
9	7	33	972	16380
10	8	39	1210	31870
11	9	47	1728	55290
12	10	56	2350	87808
13	11	65	3072	131070

The yolk sac is formed simultaneously with the amnion from the extraembryonic endoderm in the form of a yolk vesicle, which gives rise to the epithelial lining, and an adjacent layer of extraembryonic mesoderm (mesenchyme), which forms the connective tissue basis of the organ. The human yolk sac does not contain yolk, but is filled with a liquid containing proteins and salts. Unlike birds, it does not play a significant role in providing nutrition to the embryo (the nutrition of the human embryo comes from the mother’s blood). It acts as the first hematopoietic organ: from its mesenchyme the first blood vessels are formed, and inside them - blood cells (intravascular hematopoiesis). Primary germ cells (gonoblasts) appear in the endoderm of the yolk sac, which then migrate to the primordia of the gonads. After the formation of the trunk fold, the yolk sac remains connected to the intestinal tube by a small yolk stalk. Starting from the 7th - 8th week of embryogenesis, reverse development of the yolk sac is observed. The remains of the latter can be found in the umbilical cord in the form of a narrow epithelial tube.

Allantois

The allantois is formed on the 16th day of embryogenesis in the form of a finger-shaped outgrowth of the intestinal endoderm, which, heading into the amniotic leg, is surrounded by extra-embryonic mesenchyme. In birds, it performs the function of a urinary sac (it accumulates fetal excretion products that cannot be excreted in environment because of the shell). In humans, it does not reach significant development and serves to conduct blood vessels from the embryo to the chorion. Their thinnest branches, together with the mesenchyme, penetrate into its villi. Through the vessels of the allantois, in the early stages of embryogenesis, the functions of nutrition, gas exchange and excretion of the embryo are carried out. Starting from the second month, the allantois is reduced and remains in the form of a cord of cells in the umbilical cord along with a reduced yolk sac.

Chorion

The chorion, or villous membrane, is present only in placental mammals and humans. It is formed in the 2nd week of human development, when the extraembryonic mesoderm grows towards the trophoblast, forming secondary villi together with it. At the beginning of the third week, blood vessels grow into the chorionic villi, and they are called tertiary villi. Further development of the chorion is associated with the formation of the placenta.

Placenta

The placenta is the organ of communication between the fetus and the maternal body. It performs all functions necessary for the development of the fetus. Respiratory, trophic, excretory functions are provided due to the fact that oxygen and nutrients flow through the placenta from the mother's blood into the fetal blood, and in the opposite direction - carbon dioxide and metabolic products.

The endocrine function is the production of hormones that regulate fetal development and the course of pregnancy: human chorionic gonadotropin, placental lactogen, progesterone, estrogens, melanotropin, corticotropin, somatostatin and others. The protective function of the placenta is to passively immunize the fetus with the help of maternal immunoglobulins. At the same time, the placenta provides an immune barrier between the mother’s body and the fetus’ body. Many micro- and macroelements, vitamins A, C, D, E, etc. are also deposited here.

The human placenta is formed from the 3rd to the 12th week of embryogenesis. It distinguishes between the fetal and maternal parts. The fetal part is represented by the chorionic plate, from which the villi extend. The maternal part includes a part of the lining of the uterus called the basal lamina.

The chorionic plate and villi of the fetal part of the placenta are formed by loose fibrous connective tissue covered with epithelium - cyto- and symplastotrophoblast. Some of the villi reach the basal lamina of the maternal part of the placenta and attach to it, forming anchor villi. The stem villi with their branches form the structural and functional units of the placenta - cotyledons, the total number of which reaches 200. Cotyledons are separated by septa extending from the basal plate of the maternal part of the placenta. The basal lamina is the deep layer of the endometrial lining that sheds. Here, in large quantities Decidual cells are found - large, glycogen-rich cells with oxyphilic cytoplasm and large nuclei. Their participation in the immune response and hormone production is assumed.

In humans, the placenta is discoidal in shape, and hemochorial in relation to the chorion to the maternal mucosa. The last name is due to the fact that the chorion receives oxygen and nutrients directly from the mother’s blood, located in the lacunae of the mother’s mucous membrane: “the chorionic villi are bathed in the mother’s blood.”

A hemochorial (placental) barrier is formed between the mother's blood and the fetus's blood. It consists of symplastotrophoblast, cytotrophoblast, epithelial basement membrane, villous connective tissue, fetal vascular basement membrane, fetal vascular endothelium. By the end of pregnancy, the trophoblast becomes very thin or disappears, being replaced by a fibrin-like oxyphilic mass, consisting of plasma coagulation products and trophoblast breakdown - fibrinoid. Thanks to the placental barrier, normally foreign substances and bacteria do not penetrate into the fetal blood. However, it is not an obstacle to viruses, alcohol, nicotine and a number of other substances that are dangerous to the embryo, especially in the first 3 months of pregnancy, since they are not metabolized, but accumulate in its tissues and organs, as a result of which they can cause disturbances in embryonic development and deformities .

The yolk sac is an embryonic organ that contains a supply of nutrients for the embryo. The yolk sac persists throughout the first trimester and resolves on its own after 12 weeks. The shape and size of the yolk sac are one of the most important indicators of the course of pregnancy in its earliest stages.

Origin

The yolk sac is formed from a special structure - the endoblastic bladder - on the 15-16th day of embryo development (or on the 29-30th day from the last menstruation). During this period, a woman may not yet be aware of her changed status, and only a delay in menstruation indicates a possible conception of a child. The yolk sac develops together with the fertilized egg and other structures of the embryo according to a program given by nature. Any deviations from the genetically programmed rhythm can lead to termination of pregnancy.

The yolk sac is a closed ring located inside the chorionic cavity. It does not function for long - only 12-14 weeks. At the beginning of the second trimester, the yolk sac begins to decrease in size. After 14 weeks, the formation disappears without a trace, having fulfilled all its functions.

Role of the yolk sac

The yolk sac is a temporary (provisional) organ, but without it the normal course of pregnancy and embryo development is impossible. In the early stages, the size of the yolk sac exceeds the size of the embryo and amniotic cavity. The yolk sac actively grows from 6 to 12 weeks of gestation, after which it gradually decreases in size and completely disappears.

On days 18-19 from conception, the yolk sac becomes the focus of hematopoiesis. In its walls, areas of erythropoiesis are formed, and the first red blood cells are formed. Subsequently, a branched network of capillaries is formed here. Primary red blood cells, leaving the yolk sac, enter the circulatory system of the embryo and are carried through the bloodstream throughout the body.

From the 28th day from the moment of conception, the yolk sac begins to produce primary germ cells of the embryo. Subsequently, the germ cells migrate from the yolk sac and reach the gonads (sex glands). 4-5 weeks of pregnancy is an important stage in the development of the fetal reproductive system. Any negative impacts during this period (infections, radiation, intake medicines) can disrupt the formation of the gonads of the embryo and cause infertility.

From 2 to 6 weeks of pregnancy, the yolk sac acts as a liver for the embryo. The walls of the yolk sac synthesize important proteins and enzymes necessary for the normal development of the entire organism. In particular, AFP (alpha fetoprotein) is produced here. In the fetal circulatory system, AFP binds to PUFAs (polyunsaturated fatty acids) and transports them to all cells and tissues. AFP also suppresses the immune response to newly synthesized proteins, allowing metabolic processes to proceed at the desired rhythm.

Other functions of the yolk sac:

• regulation immune system fetus;
• synthesis of hormones;
• creating conditions for adequate metabolism;
• excretion of metabolic products.

The yolk sac performs all its functions until the basic internal organs and will not take on this work. After 12 weeks there is no need for a yolk sac. By the beginning of the second trimester, only a small cystic formation at the base of the umbilical cord remains from the yolk sac.

Yolk sac on ultrasound

During ultrasound examination with a transvaginal sensor, the yolk sac is detected from 6 to 12 weeks of pregnancy. Minor deviations (up to 2 weeks) in any direction are allowed. The absence of a yolk sac on ultrasound is an unfavorable sign indicating serious problems during pregnancy.

When performing an ultrasound, the doctor evaluates the location, shape and size of the yolk sac. The size of the yolk sac will depend on the gestational age.

Yolk sac norms by week:

It is important to remember: the size of the yolk sac changes rapidly in early pregnancy. Minor deviations should not frighten a pregnant woman and cannot be the basis for making serious diagnoses. If the size of the yolk sac is not normal, the doctor must carefully examine the embryo, determine the location of the fertilized egg and other parameters. If necessary, a repeat ultrasound is performed after 1-2 weeks.

Time frame for ultrasound:

• 6-7 weeks;
• 12-14 weeks.

At 6-7 weeks, the first ultrasound examination during pregnancy is performed. During the procedure, the doctor confirms the fact of pregnancy and determines its duration. The doctor indicates the location of the fertilized egg (in the uterus or outside it), assesses the condition and location of the yolk sac and chorion. The size of the fetus is determined, its correspondence to the gestational age and the size of the yolk sac. At 6 weeks, the embryo's heartbeat is also listened to and its viability is assessed.

At 12-14 weeks, the first ultrasound screening is performed. During the procedure, the doctor evaluates the condition of the embryo, chorion and yolk sac. During this period, the yolk sac reaches its maximum sizes. When performing an ultrasound at a later date, the yolk sac begins to dissolve and is not always visualized on the screen. After 14 weeks, the yolk sac is normally not detectable.

Adverse symptoms:

• absence of the yolk sac for up to 12 weeks;
• thickening of the yolk sac more than 7 mm or decrease less than 2 mm;
• change in the shape of the yolk sac.

In combination with other symptoms, these conditions may indicate a high risk of miscarriage in the first trimester. To clarify the diagnosis, additional examination using an expert-class device may be required.

Pathology of the yolk sac

When performing an ultrasound, the doctor can detect the following conditions:

The yolk sac is not visible

Normally, the yolk sac is detected by ultrasound in the period from 6 to 12 weeks. The absence of a yolk sac is an unfavorable sign. If such an important organ is resorbed ahead of time for some reason, the embryo ceases to receive the substances necessary for its development. The synthesis of hormones and enzymes is disrupted, and the production of red blood cells stops. With premature reduction of the yolk sac (before 12 weeks), spontaneous miscarriage occurs. It is not possible to maintain pregnancy with medications.

The absence of a yolk sac on ultrasound (from 6 to 12 weeks) is considered one of the signs of a regressing pregnancy. In this case, the heartbeat of the embryo is not detected, its size does not correspond to the gestational age. Treatment is only surgical. In case of regressing pregnancy, the fertilized egg is removed and the uterine cavity is curetted.

The yolk sac is smaller than normal

Possible options:

• The yolk sac is defined as a rudimentary formation.
• The size of the yolk sac does not correspond to the duration of pregnancy (smaller than normal).

Any of these situations indicates that premature resorption of the yolk sac has begun. If at the time of reduction of the sac the internal organs of the fetus are not yet formed and are not able to fully function, the death of the embryo and spontaneous miscarriage occurs. In some cases, contractions of the uterus and miscarriage do not occur after the death of the embryo. This condition is called regressive pregnancy.

The yolk sac is larger than normal

The main reason for this symptom is incorrect determination of the gestational age. This is possible with irregular menstrual cycle(against the background of various gynecological pathologies or in nursing mothers). In this situation, the doctor should evaluate the size of the embryo and recalculate the gestational age taking into account the available data.

An important point: changes in the size, shape or density of the yolk sac are important only in combination with other ultrasound indicators. If any abnormalities are detected, the condition of the embryo (location, size, heartbeat) should be assessed. If the baby is growing and developing in accordance with the gestational age, there is no reason to worry. Changes in the yolk sac in this case are considered an individual feature that does not affect the course of the first trimester.

In early pregnancy, ultrasound is performed to identify a viable embryo in the uterine cavity, confirm the gestational age, exclude pathology of the embryo or identify normal variants, for example multiple pregnancy.

The initial sign of pregnancy is thickening of the endometrium, but ultrasound does not tell what exactly causes this thickening.

Using a high-resolution transvaginal transducer, a gestational sac with a diameter of 1 mm is visualized in the uterine cavity 4 weeks and 2 days after the last menstrual period during a regular menstrual cycle.

If menstruation is delayed for 5-7 days or more (gestational age is 5 weeks), a fertilized egg with a diameter of 6 mm should be clearly visible in the uterine cavity. It has a clear round shape with a fuzzy light rim along the periphery (hyperechoic rim - chorion). In this case, the level of beta-hCG in the blood is 1000-1500 IU/l (see What is hCG?). When the hCG level is more than 1500 IU/l, the fertilized egg in the uterine cavity should be clearly visualized.

With a lower level of hCG, the fertilized egg in the uterine cavity may not be detected by transvaginal echography. With a transabdominal examination, detection of the fertilized egg in the uterine cavity is possible at a beta-hCG level of 3000-5000 IU/l.

Fig.1Uterine pregnancy 4-5 weeks. Transabdominal scanning.

IMPORTANT: The gestational age cannot be accurately determined by the size of the fertilized egg. Many tables on the Internet with the size of the fertilized egg determine the period very approximately (see table below).

From about 5.5 weeks, transvaginal ultrasound begins to visualize an extraembryonic structure in the fetal egg - the yolk sac (eng. yolk sac). At the same time, the beta-hCG level averages approximately 7200 IU/l (see. hCG norms during pregnancy).

Since the yolk sac is part of the embryonic structures, its detection makes it possible to distinguish a fertilized egg from a simple accumulation of fluid in the uterine cavity between the endometrial layers, and in most cases, makes it possible to exclude an ectopic pregnancy. The incidence of ectopic pregnancy is 1-2 per 2000-3000 pregnancies. Its risk increases with the use of assisted reproductive technologies (ART). An ectopic pregnancy should be suspected when hCG level is more than 1500 IU/l, and the fertilized egg is not detected in the uterine cavity.

Fig.2Pregnancy 5.5 weeks. The yolk sac is identified. Transvaginal scan.

From 6 weeks of pregnancy (sometimes a little earlier), an embryo about 3 mm long can be identified in the fertilized egg. From this same period, most ultrasound machines can detect the heartbeat of the embryo. If the heartbeat is not detected or is unclear when the embryo length (CTE) is 5 mm, a repeat ultrasound scan is indicated after a week. The absence of cardiac activity at this stage is not necessarily a sign of fetal distress or a non-developing pregnancy.

The numerical values ​​of the heart rate in an embryo during an uncomplicated pregnancy gradually increase from 110-130 beats/min at 6-8 weeks of pregnancy to 180 beats/min at 9-10 weeks.

The length of the embryo is measured from the head to the tail end, and is designated under the term CTE ( coccyx-parietal size), in English literature - CRL (Crown-Rump Length). It should be noted that the coccygeal-parietal size of the embryo is less subject to individual fluctuations than the average internal diameter of the ovum, and therefore, its use to determine the gestational age gives top scores. The error usually does not exceed ±3 days. With clear visualization of the embryo, the gestational age is determined depending on its length, and not on the size of the average internal diameter of the ovum (SVD).

To correctly measure the coccygeal-parietal size of the embryo, its clear visualization is necessary. In this case, one should strive to measure the maximum length of the embryo from its head end to the tailbone.

During normal pregnancy, the diameter of the ovum increases by 1 mm per day. Lower growth rates are a poor prognostic sign. With a gestational age of 6-7 weeks, the diameter of the ovum should be about 30 mm.

Table 1. Dependence of gestational age on the average internal diameter of the ovum (Dv), M. N. Skvortsova, M. V. Medvedev.

Table 2. Normal values ​​of the coccygeal-parietal size (CPR) depending on the gestational age ( full weeks+ days), data in millimeters, lower limit - 5th percentile, upper limit - 95th percentile.

It should be emphasized that determining the gestational age by the length of the CTE is best done before 12 weeks of pregnancy. At a later date, measurements of biparietal diameter, head and abdominal circumference should be used.

Fig.3 Pregnancy 12 weeks 3 days.

The motor activity of the embryo is determined after 7 weeks of pregnancy. At first, these movements are very weak and isolated, barely noticeable during examination. Then, when differentiation into the head and pelvic ends of the embryo becomes possible, movements resemble flexion and extension of the body, then separate movements of the limbs appear. Since episodes of motor activity of the embryo are very short and count in seconds, and periods of motor rest can be significant in time, registration of the cardiac activity of the embryo is undoubtedly a more important criterion for assessing its vital activity.

The diagnosis of anembryonia (empty fertilized egg) is assumed if a yolk sac is not detected in a fertilized egg measuring 20 mm. Or if the fertilized egg with a diameter of more than 25 mm with a yolk sac does not contain an embryo. And also when the yolk sac size is 10 mm or more. In any case, if anembryonia is suspected, all data obtained should be interpreted in favor of pregnancy, and the study should be repeated after 7 days.

The diagnosis of a non-developing pregnancy should not be made if, on ultrasound, the ovum is less than 20 mm in size. When the embryo is 5 mm or more in length, in most cases the heartbeat should be clearly detectable. If the embryo is less than 5 mm, the ultrasound should be repeated after a week. If, upon repeated examination a week later, at CTE = 5-6 mm, cardiac activity is not detected, the pregnancy is not viable. The diagnosis of a non-developing pregnancy can be confirmed by a discrepancy between the beta-hCG level and echographic data.

It should be noted that the normal rate of pregnancy termination in the population is 15-20% of all clinically diagnosed pregnancies. However, in reality, if we count all “chemically” diagnosed pregnancies, determined by the level of beta-hCG before the expected next period, the miscarriage rate can reach up to 60%.

Best regards, doctor ultrasound diagnostics, Barto Ruslan Alexandrovich, 2012

All rights reserved®. Quoting only with the written permission of the author of the article.

Ultrasound during pregnancy has long become an understandable and familiar procedure, because it is the simplest, most reliable and informative method of monitoring the condition of the fetus. As a rule, a diagnostic specialist also determines the duration of pregnancy during the examination, and almost every patient takes this for granted, without thinking - how exactly does the doctor determine the timing? And how accurate? What parameters does it use for this?

It is diagnostics using ultrasound that helps doctors reliably determine the timing of gestation based on indicators of a very different nature, but at the same time directly established for a more informative result.

Setting an exact date also helps predict the date of birth, which is very important both from a medical point of view and simply to reassure the expectant mother. It is also necessary to know the most accurate period in order to control the development of the fetus, its condition, and the relationship between norms and reality.

How does a specialist determine deadlines?

Some patients believe that it is enough for the doctor to look at the image on the monitor - and the “age” of the child immediately becomes visually clear, but this, of course, is not the case. The specialist records the obtained data of the embryo and compares it with the normal variants. Usually, to help the doctor, there is a special table with fixed indicators, where all the relevant norms are listed by week.

Quantitative indicators.

Table No. 1. Norms of indicators at 5-10 weeks of pregnancy.

Table No. 2. Norms of indicators for the second trimester.

11	17-21	10-16	52-73
12	22-24	17-21	58-83
13	25-27	23-28	73-95
14	28-30	27-31	84-110
15	31-33	32-39	110
16	34-37	41-49	111-135
17	38-41	45-54	122-149
18	42-47	48-59	131-160
19	48-49	52-63	142-174
20	50-53	56-67	154-186
21	54-56	61-72	167-200
22	57-60	65-76	178-211
23	61-64	68-80	190-223
24	65-67	71-85	201-236

Table No. 3. Norms of indicators for the third trimester.

Gestational age (in weeks)	BDP (biparietal size) (in millimeters)	Fronto-occipital size (in millimeters)	Head circumference (in millimeters)
25	68-70	73-88	215-250
26	71-73	76-93	224-261
27	75-76	80-96	235-273
28	77-79	83-98	245-284
29	80-82	86-101	255-295
30	83-85	89-104	265-304
31	86-87	93-108	273-314
32	88-89	95-112	283-325
33	90-91	98-116	289-332
34	92-93	101-119	295-338
35	94-95	105-120	299-345
36	96-97	104-123	303-348
37	98-98	106-126	307-352
38	99-100	108-128	309-357
39	101-102	109-129	311-359
40	103	110-120	312-361

Table No. 4. Standards for fetal length.

Gestational age (in weeks)	Embryo dimensions (in centimeters)
5	0,8
6	1,1
7	1,3
8	1,5
9	2,2
10	3,2
11	4,1
12	5,3
13	7,5
14	8,7
15	10
16	11,5
17	13,1
18	14,2
19	15,2
20	16,5
21	26,6
22	27,8
23	29,8
24	31
25	34,6
26	35,5
27	36,5
28	37,7
29	38,6
30	39,8
31	41,1
32	42,5
33	43,6
34	45
35	46,1
36	47,3
37	48,6
38	49,8
39	50,6
40	51,7
41	52
42	53

Table No. 5. Standards for the abdominal circumference of the embryo.

Gestational age (in weeks)	Abdominal circumference (in millimeters)
11	40-61
12	50-71
13	58-79
14	66-91
15	91
16	88-115
17	93-130
18	105-144
19	114-154
20	125-163
21	137-177
22	148-190
23	160-201
24	173-223
25	183-228
26	194-240
27	206-253
28	217-264
29	228-277
30	238-290
31	247-300
32	258-314
33	267-334
34	276-336
35	285-344
36	292-353
37	300-360
38	304-368
39	310-375
40	313-380

Table No. 6. Norms for placental thickness.

Gestational age (in weeks)	Optimal placental thickness (in millimeters)
20	22-23
21	22,8-23,5
22	23,6-24,4
23	24,5-26
24	25,3-25,8
25	26,2-26,7
26	27-27,5
27	27,9-28,3
28	28,7-29
29	29,6-30
30	30,4-30,7
31	31,3-31,8
32	32,1-32,5
33	33-33,4
34	33,9-34,3
35	34,7-35
36	35,6-36
37	34,3-34,7
38	34,1-34,5
39	33,8-34
40	33,5-33,7

What exactly does the specialist analyze?

The analyzed norm indicators depend on the trimester and the specific period.

In the first trimester Special attention is paid to the length of the fetus, since this is the only parameter that provides reliable information. During this period, there are no decisive differences in the development of embryos, so ultrasound establishes the “age” of the child accurate to the day.

The second and third trimester are periods during which absolute accuracy cannot be achieved, because from this moment the embryos begin to develop individually. Doctors use average statistical figures, but even in this case, the period is set as reliably as possible, and it is very possible to identify possible pathologies. At the same time, specialists analyze such indicators as the circumference of the child’s head, diameter chest, coccyx-parietal distance of the embryo.

Now it is necessary to analyze in more detail the meaning of the indicators presented in these tables, which may raise questions among patients.

Coccygeal-parietal distance - the distance, respectively, from the crown of the embryo to the coccyx. Thanks to this indicator, the most accurate determination of the period is possible, because these sizes are universal. Also, if there are factors that prevent the establishment of deadlines, KTR is the only reliable parameter in this case.

The diameter of the fertilized egg is the directly fertilized egg from which the embryo will develop in the future. Its dimensions, of course, directly depend on the specific period and have been studied for a long time - the doctor just needs to look at the corresponding table.

The diameter of the yolk sac is also an important indicator b, since the yolk sac plays a very important role throughout the development of the child (for example, in the first trimester it supplies the circulatory system of the embryo with nuclear red blood cells). The doctor always has the dimensions in the table.

Biparietal size– the distance between the parietal bones of the embryo.

Fronto-occipital size– the distance between the frontal and occipital bones, respectively.

Embryo length– is calculated when the child is in the most “unbent” state.

Placenta thickness– a lot depends on the placenta: it protects the child, supplies him with everything he needs, and produces many hormones. Therefore, it is very important to check that its thickness meets the specified deadlines. If the mother’s condition is stable, there are no deviations - it is enough to simply determine the “age” of the embryo by the thickness of the placenta.

Accuracy

Many women are interested in how accurately does fetal ultrasound help determine the timing by week? Therefore, it is important to note that ultrasound diagnostics establishes obstetric timing, in other words, the “age” of the embryo is calculated from the first day of the last menstruation. Sometimes a situation arises when a patient, checking tables on the Internet and ultrasound results, discovers differences in the period, so you need to know exactly what system was used to calculate, and not “sin” for the imperfections of ultrasound diagnostics.

Pathologies

Fetal ultrasound is informative not only as an aid in determining the due date, but also in detecting pathologies of various types. Moreover, some of them can only be detected using ultrasound, it is also important to note that since ultrasound can be done as often as desired, it is sufficient effective method monitoring the condition of the fetus.

So, the main pathologies that can be identified are:

1. Developmental delay (identified by comparing normative parameters with reality; indicators below the threshold undoubtedly indicate the presence of an anomaly).
2. Various defects (also detected when indicators do not match).
3. Low water.
4. Polyhydramnios.
5. Thickening of the placenta.
6. Non-developing pregnancy (indicators below standards (especially coccygeal-parietal size) in the first trimester).

When can I go to the diagnostic room?

Of course, modern ultrasound technologies make it possible to detect an embryo a week after conception, but most clinics still do not have such advanced equipment. It is also important to note that this will require a transvaginal ultrasound, which is very dangerous for the unborn child and can cause spontaneous miscarriage. The examination can be done so early only if there are special medical indications; in any other case, you can be patient with knowledge of the exact date.

It is recommended to contact a diagnostician at the 5th week of pregnancy, when it will be possible to examine the fetus in more detail using ultrasound, draw certain conclusions and determine the due date with maximum accuracy.

Is it dangerous?

Some patients refuse ultrasound diagnostics using both the transvaginal and transabdominal methods, citing the dangers of ultrasound. Indeed, these fears are logical, because caring for the baby’s health is common to any mother. But ultrasound is not at all dangerous for the embryo; even at a short period of time, there is no reason to believe that ultrasonic waves will harm the development of the child, cause pathologies or cause a miscarriage.

Probability of error

Any woman can quite rightly consider that the size of the embryo is not the most reliable indicator for setting the due date, because each child develops differently and it is difficult to determine its exact age. But in fact, after years of medical practice, there is no longer any doubt about the correctness of the fetal due date established on ultrasound.

If a woman still questions the ultrasound results, she can always carry out a number of additional diagnostic procedures, which in turn will allow her to determine the timing at the most accurate level.

Fetal ultrasound is not only a method of monitoring the condition of the fetus, monitoring its development, but also a completely reliable, accurate, informative, convenient and simple way to determine the period by week. Based on many parameters, which have already been quite fully studied over the years of development of ultrasound medicine, the diagnostician quickly determines the obstetric “age” of the embryo, using special tables that a simple patient can rely on.

What is SVD during pregnancy and how to determine it on ultrasound? There is only one answer to this question.

SVD is the average internal diameter of the ovum according to ultrasound diagnostics. This indicator is measured exclusively in millimeters.

Fertilized egg illustration

The gestation period is characterized by certain values ​​of the internal diameter. The digital value of the SVD constantly varies, so the period is calculated with an error of a week to a week and a half. A more reliable sign is the CTE (coccygeal-parietal size) indicators. It should be noted that the coccygeal-parietal size of the embryo is less subject to individual fluctuations compared to the average internal diameter of the ovum, and therefore is used more often to establish a reliable gestation period. The error is approximately three days.

When the fetus is well visualized, the period is determined by the length of the fetus, and not by the internal diameter. The coccygeal-parietal size is recorded during a routine ultrasound and reflects the actual size of the fetus in combination with the approximate weight of the fetus. As a rule, the measurement of CTE indicators is used before, and in later ultrasound studies, the biparietal diameter of the circumference of the head and abdomen of the fetus is used.

Approximate indicators of SVD, depending on the timing of gestation

• When the diameter of the fertilized egg is approximately 4 millimeters, then the gestational age is. It is possible to assume that about four weeks have passed since conception.
• Closer to the fifth week, the diameter will reach 6 millimeters.
• After a few days, the fetus becomes 7 millimeters.
• the diameter increases to 12 - 18 millimeters.
• The average value of SVD at a period of six weeks and five days is 16 millimeters.

Fertilized egg on ultrasound

Of course, the expectant mother is concerned about the following question: how intensively does the fetus grow in the second and third trimester? We can say with confidence that its diameter is growing by one millimeter every day. Then its value increases by an average of 2 - 2.5 millimeters every day. During the border period of 16 - 17 weeks, they stop measuring the internal diameter of the fetal egg, focusing on more reliable indicators.

Ultrasound examination at short gestation

Diagnostics are carried out for the following purposes:

Diagnosis of the localization of the ovum

1. Establishing the exact location of the fetus (in the uterine cavity or outside it). When the fetus is located outside the uterus, we are talking about it. When the fetus cannot be visualized or the recognition process becomes significantly more difficult, they resort to precise definition embryo heartbeat. Signs of fetal viability may be found in the fallopian tubes or abdominal cavity.

In addition to this complication, other complications may appear in the initial stages of pregnancy: for example, a changed shape of the fertilized egg; improper attachment; high risk of placental abruption and other pathological disorders.

2. Determining a single or multiple pregnancy is not difficult. In the uterine cavity there are two or more fetuses with active life activity.

3. Assessing the main dimensions of the fertilized egg and embryo and comparing them with normal values.

4. Study of the correct structure of the embryo and fertilized egg to exclude serious congenital developmental anomalies. These may be chromosomal mutations (for example, Down syndrome).

5. Vital signs are assessed based on the presence of a heartbeat, which is detected already in the fifth week of gestation. The motor activity of the embryo is quite well determined after the seventh week of gestation.

At the initial stage, the movements are so weak and isolated that they can hardly be distinguished during an ultrasound. As the embryo grows, motor activity begins to resemble characteristic flexion and extension movements, and then active movements of the upper and lower limbs. Since certain moments motor activity are quite short in time and counted in seconds or their fractions, then to register the fact of fetal life, the definition of cardiac activity is used.

6. . This small cystic formation provides the body expectant mother important hormones for preserving the fetus in the early stages of development.

7. The study of amnion and chorion comes down to their ratio depending on the period of gestation already in the first trimester. Based on the obtained ultrasound results, it is possible to predict the further course and outcome of pregnancy.

Ultrasound is indispensable for determining possible problems with pregnancy

8. Diagnosis of threatened miscarriage using ultrasound allows you to recognize early symptoms, which are characterized by a clear thickening of one of the walls of the uterine cavity, as well as a significant increase in the internal pharynx. In case of a possible miscarriage, ultrasound assesses the vital signs of the fetus and the condition of the uterus and placenta as a whole.

9. Diagnosis of diseases and possible malformations of the female genital area (anomalies of the vagina or uterus). Any deviation from the norm determines the course and outcome of pregnancy.

Typical signs and features of fertilized egg implantation

Often, the fertilized egg attaches to the wall of the uterus several days after unprotected sexual intercourse, and then the egg is implanted into the endometrial layer after fertilization. WITH at this moment the woman's body begins to actively produce the hCG hormone ( human chorionic gonadotropin), to which the pregnancy strip test reacts.

Implantation of fertilized egg

The screening test will not always be positive, so it is necessary to resort to a reliable blood test to determine hCG. After receiving a positive test result, you must as soon as possible contact a gynecologist at the antenatal clinic for registration and further monitoring for nine months.

The formed fertilized egg is the most sure sign the onset of pregnancy. It has a characteristic oval shape and is quite well visualized on ultrasound in the third week of absence of menstruation.

The embryo itself can only be seen when the period reaches the fifth week. If the ultrasound doctor does not detect an embryo in the fertilized egg, then the study is repeated after about half a month. Typically, the embryo becomes more clearly visible and its heartbeat is detected. In other cases, we are talking about pathological development or even a frozen and undeveloped pregnancy.

That is why it is very important to undergo an ultrasound to exclude possible complications for further correction of the situation. The first trimester is the most important period of gestation, since throughout its entire duration all the organs and systems of the unborn baby are actively formed.

Timing of routine ultrasound diagnostics

Based on the results of the WHO, strict periods have been defined for conducting mandatory ultrasound examinations during the gestation period of the unborn baby.

Three ultrasound screenings are required

At other time intervals, the examination is prescribed strictly according to individual indications from the mother and fetus:

• recommended at 12 - 14 weeks;
• for 20 - 24 weeks;
• necessary at 32 - 34 weeks of gestation.

It is not advisable to neglect the timing of the next examination, since it is during the specified period of gestation that it is possible to recognize fetal malformations. And if a forced need arises, an interruption for medical reasons. The last screening examination can also be carried out at a later time.

The results of current diagnostics may be significantly outside the scope normal indicators, but this is far from a cause for concern. Do not forget that the development of each child has its own characteristics. However, you should not ignore the identified symptoms either.

) ultrasound examination is carried out to establish the localization (location) of the fetal egg. The fertilized sac is a round or ovoid (egg-shaped) formation that surrounds the embryo, usually located in the upper half of the uterine cavity. On an ultrasound, the fertilized egg looks like a small dark gray (almost black) spot with clear contours.

The presence of a fertilized egg in the uterine cavity eliminates the possibility ectopic pregnancy. In a multiple pregnancy, you can see two separately located fertilized eggs.

At what time can you see the fertilized egg?

Approximately two and a half weeks after conception, if menstruation is delayed by 3-5 days or more, that is, in the fourth to fifth obstetric week of pregnancy from the last day of the last menstruation, an ultrasound diagnostician can already see the fertilized egg in the uterine cavity using transvaginal ultrasound. The diagnostic level of hCG in the blood serum, at which the fertilized egg should be visible in the uterine cavity during transvaginal ultrasound, is from 1000 to 2000 IU.

The fertilized egg looks like a rounded black (anechoic or echo-negative, that is, not reflecting ultrasonic waves) formation, the diameter of which is very small and ranges from 2-3 mm. The embryo and extra-embryonic organs still have a microscopic structure and therefore are not yet visible using ultrasound. Using a parameter like average internal diameter of the ovum It is most advisable in the first 3-5 weeks of pregnancy from conception, when the embryo is not yet visible or is difficult to detect. The error when using a measurement usually does not exceed 6 days.

Fertilized egg: size by week

The size of the ovum by week is a very important indicator during pregnancy. For example, a gestational sac diameter of 3 mm corresponds to a gestational age of 4 weeks, and a gestational sac diameter of 6 mm corresponds to a gestational age of 5 weeks. An increase in the average diameter of the ovum occurs in the early stages of pregnancy at a rate of approximately 1 millimeter per day.

Most standard indicators for the average internal diameter of the ovum are limited to a period of 8-10 weeks. This is due to the fact that after 6–7 weeks of pregnancy, the size of the fertilized egg cannot reflect the growth of the embryo. With its advent, the coccygeal-parietal size of the embryo (CTE) is used to estimate the gestational age.

The dimensions of the average internal diameter of the ovum by week are given in the calculator.

Irregularly shaped ovum (deformed ovum)

If the fertilized egg is located in the uterine cavity, then such a pregnancy is called physiological intrauterine pregnancy. A fertilized egg up to 5-6 weeks normally on ultrasound has a round or drop-shaped shape, surrounded by a thin membrane. By 6-7 weeks, it completely fills the uterine cavity and acquires an oval shape in a longitudinal scan, and a round shape in a transverse scan. If on an ultrasound the doctor sees a deformation of the fertilized egg (it is elongated, flattened on the sides, looks like a bean), then this may indicate uterine tone. A change in the shape of the fertilized egg is also possible with partial detachment. Significant deformation with unclear contours is observed during frozen pregnancy.

Timely diagnosis of deformation of the ovum during pregnancy makes it possible to save the child.

Empty fertilized egg

Normally, the fertilized egg in the uterine cavity is visible on transvaginal ultrasound approximately 32-36 days after the first day of the last menstrual period. An important place is given yolk sac, which is of great importance in the development of the fertilized egg. During the physiological course of pregnancy, the yolk sac has a round shape, liquid contents, and reaches its maximum size by 7–8 weeks of pregnancy.

The embryo appears as a thickening along the edge of the yolk sac. The image of a normal embryo with a yolk sac looks like a "double bleb". By seven weeks, the yolk sac measures 4-5 mm. A relationship has been established between the size of the yolk sac and pregnancy outcome. When the diameter of the yolk sac is less than 2 mm and more than 5.6 mm, spontaneous miscarriage or non-developing pregnancy is quite often observed at 5–10 weeks.

The absence of a yolk sac with an average internal diameter of the ovum of at least 10 mm is an unfavorable ultrasound criterion for the threat of miscarriage.

An empty (false) ovum is an accumulation of fluid, usually irregular in shape, located near the border of the endometrium.

Sometimes there are cases when the fertilized egg has the usual shape and size, but there is no yolk sac or embryo inside it. The chorion of an empty fertilized egg produces the hCG hormone, as in normal physiological pregnancy, so pregnancy tests will be positive. An ultrasound performed in the early stages of pregnancy can be erroneous, since the earlier it is done, the less chance there is of seeing the embryo. Before 7 weeks of pregnancy, a repeat study is required to clarify the diagnosis.

When on an ultrasound they see a fertilized egg in the uterine cavity, but do not see the embryo itself, doctors call this pathology anembryony (without embryo).

The following signs indicate a non-developing pregnancy (death of the embryo): altered membranes, the absence of an embryo when the size of the fetal egg is more than 16 mm in diameter or the absence of a yolk sac when the membranes are more than 8 mm in diameter (when performing a transabdominal ultrasound: 25 mm - without an embryo and 20 mm – without yolk sac); uneven contours, low position or absence of the double decidual sac.

IN early dates The cause of pregnancy loss is most often chromosomal abnormalities that arose during the process of fertilization.

If a doctor finds a fertilized egg in the uterine cavity during an ultrasound, then you can congratulate the woman on her pregnancy. This formation in the uterine cavity is the very first and most important sign of the development of pregnancy.

The formation contains the embryo as well as amniotic fluid. Depending on the shape, size and location of the structure, the doctor determines the nature of the pregnancy.

Having learned about their pregnancy, many curious expectant mothers begin to ask the doctor questions about how and at what stage the fertilized egg is visible and what it looks like. We will try to answer them.

The fertilized egg, the diameter of which is very small in the first days of pregnancy, can be seen within two to three weeks after a missed period. The formed structure in most cases is located in the upper part of the uterine cavity, has a dark (gray) tint and a round or oval shape. The embryo at this time is still microscopic in size, so it is not detected.

Development and structure

The growth of the fertilized egg begins from the moment of conception. The fertilized egg begins to move through the fallopian tube, during which cell fragmentation occurs. Making its way to the uterus, the fertilized, crushed egg needs nutrients and oxygen, so after a week a chorion begins to form on top, which subsequently transforms into.

The surface of the chorion has villi, which help the formation to attach to the uterus. In the future, these villi are contained only at the site of implantation of the formation into the uterine wall. The rest of the structure loses villi and remains smooth. The chorion provides the fetus with all vital functions, one of which is protection against infections.

A value less than 7 mm indicates the middle of the fifth week. This is one of the most important periods when active formation of blood vessels, heart and nervous system. The size of the embryo is usually 2 mm.

When an ultrasound shows a fertilized egg measuring 10 mm, this indicates that the heart and blood vessels are already fully formed and the embryo has a neural tube with a slight thickening at the end (the future brain).

6 obstetric week visualizes a value of 12 mm. At the 6th obstetric week, the fertilized egg is 12 mm in size, has a spherical shape, the embryo looks like a white stripe about 5-6 mm long. At this point, the heart rate is 110-130 per minute. If any abnormality is detected during the sixth week, a repeat examination a week later is recommended.

To correct the situation, doctors remove it, after which the egg takes the correct shape. What the fertilized egg looks like during a miscarriage depends on the gestation period. At 1-2 weeks, a miscarriage may look like menstrual bleeding. At later stages, the formation looks like a blood clot. If a miscarriage occurs at 7-9 weeks, the woman may find pieces of fetal tissue.

If the structure has an oval and at the same time flat shape, this may also indicate. However, in the absence of pain and other ailments, it makes sense to continue monitoring the pregnancy. Repeated examination will allow the doctor to draw the correct conclusion.

Wrong location

A low gestational sac does not indicate a serious pathology, but requires more careful monitoring throughout pregnancy. If the formation is very close to the cervix, then it may occur cervical pregnancy, which is fraught with removal of the uterus.

Empty fertilized egg

When you can detect an empty fertilized egg, when the cavity contains only liquid or a blood clot.

Types of ultrasound. What are SVD and KTR?

To determine the parameters of the fertilized egg, different kinds Ultrasound:

• Transabdominal - examination occurs through the outer abdominal wall.
• Transvaginal – examination is carried out through the vagina.

During TA examination, clear identification of formation is possible starting from 5 obstetric week. At this time, the fertilized egg is 5-8 mm in size. Using the second research method, you can determine the size of the fertilized egg on the 3-6th day of missed menstruation, which is 4-5 weeks of gestation. The embryo is visualized starting from the 5th week of pregnancy during a TV examination, and during TA - from the 6th week in the form of a linear formation.

To assess the size and growth of the formation and embryo, the following indicators are used:

• SVD is the average internal diameter of the fertilized egg.
• KTP – coccygeal-parietal size of the embryo/fetus.

SVD shows the size of the fertilized egg by week and is measured in millimeters. So the indicator of the size of the ovum constantly varies by week of pregnancy; the CTE indicator is more accurate for determining the reliable gestation period. At this study the error may be three days up or down. Basically, the study is carried out up to 12 weeks of gestation.

The size of the fertilized egg helps to quickly determine how far along the pregnancy is and how the fetus develops in the womb. The first three months of development are the most important, because it is during this time that all the organs and systems of the future baby are actively developing. Accordingly, it is important to undergo a scheduled ultrasound on time, which helps to identify possible deviations and carry out optimal correction of the current situation.