Identical twins and fraternal twins - multiple pregnancy. How do you know if twins are identical? Can fraternal people be twins?

Cases when not one, but two or more babies settle in a mother’s belly do not occur very often - 1.5-2.5% of all pregnancies. How does this work? How is multiple pregnancy different? Is it possible to plan for twins? Our expert - Anna Romanovna PASTUKHOVA, an obstetrician-gynecologist at the Zdravitsa family medicine centers, answers all questions.

What are the chances of getting pregnant with twins?

First, some statistics. As we have already mentioned, this amazing phenomenon occurs in 1.5-2.5% of pregnancies observed in European countries. It is believed that the appearance of twins, triplets and twins is genetically determined - more often they are born in families where one or both parents were born as a result of multiple pregnancies. However, there are other reasons, including .

• The birth of twins occurs with a frequency of geometric progression; obstetricians even have a special formula: for 87 births there is one twin, for 87 twins there is one triplet, for 87 triplets there is one quadruplet, etc. True, today this formula needs correction - multiple pregnancies have become more and more common.

• Identical or identical twins are less common, with an average of 1 in 250 births.

• Most often, multiple pregnancies occur in Africa, least often in Asian countries.

Types of multiple pregnancy

Let's start with a well-known fact. There are two types of twins: identical or monozygotic and fraternal (they are also called dizygotic).

• Monozygotic twins result from the division of one egg fertilized by one sperm. They surprise everyone with their striking similarities.

• Fraternal twins are the result of the fertilization of several eggs by several sperm. They can be either the same or different sexes, often differ in character and are not always similar in appearance.

Expert commentary

Multiple pregnancy- this is a pregnancy when not one fetus develops in the mother’s body, but several at once. In medicine, a distinction is made between identical and fraternal twins (triplets, etc.). Identical twins are always the same sex, have the same blood type, and look very similar. Fraternal twins have phenotypic differences (eye color, facial features), they can be either identical or different group blood. Fraternal twins can be of different sexes.

How are identical twins made?

To be honest, we have no idea! The reasons why, instead of a single baby, two (three, four) appear from one egg and one sperm are not really known - it’s a miracle, and that’s all. The mechanism of the appearance of monozygotic twins, however, is described in sufficient detail. Everything begins as if nothing had happened: one egg, one sperm, meeting, fertilization... Then the resulting zygote begins to divide, grow and, at some point, under the influence of not entirely clear factors, suddenly splits into two or more parts, each from which it begins to live its own life.

Expert commentary

The development of identical twins occurs when one sperm fertilizes one egg, during the process of separation ovum into two, three or four parts at different stages of its development. In this case, each part develops as a separate organism. It is assumed that such separation can occur when implantation (attachment) of the fertilized egg is delayed due to oxygen deficiency. The occurrence of identical twins is also associated with the fertilization of an egg that had two or more nuclei.

Do twins interfere with each other?

It is very important at what point the splitting of the egg occurs, since the further intrauterine development of the twins depends on this.

There are 3 options for the development of monozygotic twins

• The separation of the fertilized egg occurred in the first five days after fertilization. In this case, both future babies begin to develop completely independently, each “grows” its own placenta and . Until recently, it was believed that this development was characteristic exclusively of fraternal twins and identical twins in such cases were mistakenly identified as dizygotic (maybe this is what happened with the Olsen sisters?)

• The zygote split approximately 5-8 days after fertilization. By this time, the outer membrane has already begun to form: remains common among babies, but the inner membrane of the fetus (amnion) develops in each individual. If babies have a common placenta, then one child can suppress the other - their competition begins from conception.

• Separation occurred on day 8 or later (1% of all monozygotic twins). At this time, the amniotic sac is already beginning to form, so the separated embryos will grow in the common amnion and common fetal fluid. This situation is not considered the most favorable; there is a risk that children each other.

The life of fraternal twins in the womb is organized with great comfort: each of them develops their own personal placenta (sometimes they are fused with walls), which means that the babies do not need to seriously compete for a place “in the sun.”

So, if the embryos have different placentas, then most likely they are fraternal, and if the babies “settled” with a common placenta, then these are identical twins who will be born similar as... twins.

Expert commentary

The following types of multiple pregnancy are distinguished:

• Monochorionic monoamniotic twins, when there is a common placenta and there is no septum between the twins. It's always identical twins
• Monochorionic diamniotic twins, when there is a common placenta and septum, i.e. each fetus has its own amniotic sac
• Dichorionic diamniotic twins, when each fetus has its own placenta and amniotic sac.

How do you get fraternal twins?

Non-identical twins develop from two or more fertilized eggs. How does this happen? The most common reason for this is the so-called “multiple ovulations,” when several mature eggs are released from one or both ovaries at once. The reasons for this phenomenon may be different: genetic predisposition, artificial ovarian stimulation, the first cycle after discontinuation of hormonal contraceptives.

Do you know that....

• The difference in the time of conception of fraternal twins can be from several hours to several days.

• In very rare cases, a new one is added to an existing pregnancy. As a rule, after fertilization and implantation of the fertilized egg, ovulation is immediately blocked. If, due to hormonal imbalance, this mechanism does not work immediately, the older child is supplemented with younger brother or little sister.

The existence of twins has always attracted the interest of not only science, but also, of course, the parents of twins themselves.

Who are monozygotic twins and how are they made?

Monozygotic or identical twins are two babies who develop from one egg fertilized by one sperm.

After the egg is fertilized, division occurs. If this separation is observed in the first three days, which happens in approximately 20-30% of twin pregnancies, each baby receives its own placenta and amniotic sac. In this case, the twins are called dichorionic and diamniotic twins.

Most often, the division occurs on fifth to eighth beats. Then the babies have a common placenta (monochorionic), each fetal bladder has its own (diamniotic). This happens in 70-80% of pregnancies with monozygotic twins.

If the separation occurred on the ninth or tenth day after fertilization, the children will have one placenta and one amniotic sac (monochorionic and monoamniotic twins). The probability of such a development is 1% of all cases of carrying monozygotic twins, and this option is the most difficult and dangerous for children.

In extremely rare cases, separation occurs even later. Then complete separation is no longer possible and Siamese twins are born.

What is the pregnancy rate for monozygotic twins

Cases of development of identical twins account for only a third of all cases of twin births. The remaining two-thirds are dizygotic twins, that is, identical twins. Twins can have different genders and be completely different from each other, while identical twins always have the same gender and are like two peas in a pod.

According to statistics, only three out of a thousand pregnant women carry monozygotic twins.

What factors influence pregnancy with identical twins?

Unlike dizygotic twins, the appearance of identical twins is not affected by the race and age of the woman.

It is believed that the reason for the division of the egg into two embryos is a delay in its implantation, as well as a lack of oxygen saturation.

Risk levels for multiple pregnancies

A multiple pregnancy presumably carries more danger for the mother and babies than a single pregnancy. A mother’s body needs more strength to bear two children.

In women pregnant with twins, the likelihood of developing anemia increases, and the risk of preeclampsia also increases.

In addition, multiple pregnancies have specific dangers that are not present when carrying one child:

• feto-fetal blood transfusion syndrome - a violation of the blood flow of the placenta, when more blood flows to one baby than to the other;
• reverse arterial perfusion is a pathology in which one of the fetuses may be missing an organ (heart) or part of the body (head);
• death of one of the fruits;
• congenital malformations of one of the fetuses;
• chromosomal pathology of one of the fetuses;
• Siamese twins.

Babies that a woman gives birth to as a result of one pregnancy are called twins. Such children arouse genuine interest among their peers and even adults. After all, cases of multiple pregnancies are much less common than singleton pregnancies. There are identical and fraternal twins. They are also called monozygotic and dizygotic. Their conception is influenced by various factors. It is noted that such male babies are born more often.

Difference between identical and fraternal twins

Monozygotes are born when several sperm fertilize one egg, which splits into two or more halves. They develop separately and may have a common or different placenta. Such children have the following characteristics:

• they must be of the same sex;
• outwardly they look absolutely the same;
• they have completely identical fingerprints;
• their blood type is also the same;
• usually they are similar in temperament and character;
• they are predisposed to the same diseases.

All this is explained by an identical set of genes. Actually, how do identical twins differ from fraternal twins, who have different genotypes?

But in some cases, mirror features in appearance are possible. For example, one of the children may be right-handed and the other left-handed. Dizygotic conception occurs from separate eggs fertilized by different sperm. This can happen if female body In one cycle, several eggs mature at once. There are a number of reasons for this. Children have different appearance, character, and temperament from each other. These can be babies of the same or different sexes. These are just brothers or sisters who were born on the same day. Identical twins are born less frequently than fraternal twins and make up about a third of the total.

In medical practice, all children born during one pregnancy are called twins. In common parlance, some babies are also called twins. In this regard, the question arises: how are twins different from fraternal twins? The difference lies in the mechanism of fertilization.

Twins are one face and body, like two peas in a pod. They are very close spiritually and physically. Often such people get sick at the same time, even if they are at a distance. Twins feel each other. The same cannot be said about twins. They can be completely different, there are even cases when children were born from different fathers during one pregnancy.

How do you get twins and twins?

The appearance of two babies in the womb at once does not mean that they will be exactly the same. There are three options for the development of events here. In medical practice they are characterized as follows.

• Identical (identical). Such children are obtained from one egg, which, for reasons unknown to science, is divided into 2, and in rare cases, into 3 parts. Children have the same gender, set of chromosomes, blood type and often identical fingerprints. In 25% of cases, the features of monozygotic twins are a mirror image of each other, which is especially evident in moles.
• Semi-identical (polar). This is a very rare case, as a result of which children are born with a 75% match of the genotype. They combine the characteristics of identical twins and twins. Such babies are born as a result of fertilization of one egg by two different sperm and its polar body. Moreover, the offspring can be either single- or heterosexual.
• Fraternal (dizygotic). Such babies are produced due to the fertilization of different eggs. Their set of genes coincides by 50%. Twins can look completely different and have different genders.

Here are the main differences between twins and twins. But if you delve into the details, you can find quite a few more inconsistencies.

Identical embryos coexist in the womb different conditions. It happens that they are formed in the same amniotic sac and with a common placenta. It is possible that the embryos have their own bubble, but a common placenta. And the third case is that each baby has its own placenta and amniotic sac.

When a dizygotic pregnancy occurs, the fetuses have a separate placenta and amniotic sac.

Features of monozygotic twins

It is impossible to plan to conceive identical twins. In this case, nature is in charge. Heredity and parental age are not fundamental factors. Identical babies are born quite rarely - about 1 time in 3.5-4 thousand births.

These children have the same appearance. Even close relatives often confuse them when the children are too young. Identity lies not only in the same eye and hair color, but also in the peculiarities of the body structure and the location of the teeth.

Another fact that is relevant for twins is that organ and tissue transplants between them are 100% successful. Scientific studies have shown that monozygotic children have almost identical brain electrical activity curves.

Identical twins are believed to have a special blood connection. They not only think alike, but also often love the same people. It is worth assuming that their tastes in cinema, music and other areas of art completely coincide.

Features of dizygotic pregnancy

Twins, a boy and a girl, are not uncommon. If you're lucky, they'll add one, two, or even more babies. The world knows of cases where a woman gave birth to 11 dizygotic twins at one time. But, unfortunately, none of them survived. The story of the birth of eight babies at once is more successful - each of them turned out to be healthy.

The likelihood of such a pregnancy increases due to hormonal therapy. It is prescribed for the treatment of infertility. As a result, the amount of follicle-stimulating hormone is quite high, which leads to the production and maturation of several follicles at once. Usually the eggs are released simultaneously and, under favorable conditions, are fertilized.

IVF also increases the likelihood of multiple pregnancies. Several zygotes are transplanted into patients at once. There are frequent cases when a lot of material takes root, so the doctor recommends removing part of it. This procedure ensures normal development of embryos.

Experts note that women after 35 years are more likely to give birth to twins. Such a pregnancy can be planned. If there have been cases of dizygotic twins in the family, then the chances of having double offspring immediately increase.

Twins are born much more often than identical twins. This happens 1 time in 90 births. But triplets are a rarer occurrence, occurring once in 8,000 births.

How to diagnose twins and twins

This process is quite exciting for future parents. It has the following features.

• Diagnosis occurs using ultrasound. In the early stages, a specialist can only identify larger size uterus than in a normal pregnancy, and two beating hearts.
• From 4-5 weeks, the doctor will accurately determine the number of embryos. However, whether it will be twins or twins, the parents will find out only after the birth.
• Expectant mother and father can be confident that they are expecting dizygotic twins if they have undergone IVF.

Features of education

In this case, parents have a double burden, because raising children of the same age who are also so similar in appearance is quite difficult.

Often one of the children becomes the leader. He is the instigator of various pranks and constantly provokes his brother or sister to do bad things. The second child becomes a follower and carries out all the “assignments”. Mom and dad need to explain to their children that they are equal to each other. It is important to distribute parental care and care evenly so that one of the kids does not feel deprived.

Don't compare children. Each of them is an individual with his own character and ambitions. Even if one of the twins has some kind of defect or deficiency, you should not focus on this. In addition, it is necessary to find some distinctive ability or talent in the child and develop it. Call children by name as often as possible, and try not to generalize, especially if one of the twins has done a bad thing.

The parents' task is also social adaptation kids. You shouldn’t limit their social circle to just each other. Take the kids out for a walk where they will interact with different kids. When the twins grow up a little, gradually develop their independence from each other. To do this, occasionally organize separate trips to the playground or to the cinema.

A common mistake many parents make is buying identical clothes and gifts for twins. In infancy, this is allowed, but with age it is worth abandoning such an idea. Give kids the right to choose. For a birthday, order not one large cake, but two small ones, so that each child has his own celebration.

Twins and twins are different phenomena. The following information will not only confirm this, but may also be new to you.

1. In ancient times, it was believed that the birth of two identical children was the result of the intervention of evil spirits.
2. There are special diets that supposedly allow you to conceive twins. But their effectiveness has not been proven.
3. Twins are like children of the same parents, born at different times. Not only can they have different sexes, but also different fathers and even skin color.
4. Conjoined twins are identical twins whose division began at a late stage. Because of this, they are born fused. In more successful cases, children have one area of ​​skin between them, and in very complex cases, the spine.
5. Dizygotic twins are born at different rates on different continents. The leaders in this case are African countries, and Asia, in particular Japan, closes the list. Europe is characterized by average indicators.
6. Even if identical twins are raised in different environments and are far from each other, they remain similar, have the same development and suffer the same diseases.
7. Adult dizygotic twins often grow apart from each other. They are implemented in different spheres of life and communicate with different people. But identical twins, on the contrary, are getting closer every year.

Although twins and twins are forced to live together until they grow up, parents still need to develop them as individuals. You should not identify twins, especially identical ones, even despite their external similarity.

comparison table

To make it clearer to our readers how twins differ from twins, we have compiled a comparative table.

Index	Identical (identical, monozygotic)	Polar (semi-identical)	Fraternal (dizygotic)
Features of fertilization	The result of the division of one zygote	Fertilization of one egg and its undead polar body	Fertilization of two or more eggs that mature at the same time
Genotype matches	100%	75%	By 50%
Blood type	Same	Same	Same or different
Floor	Same-sex	Same-sex or different-sex	Same-sex or different-sex
Appearance	Absolute similarity, in 25% of cases mirror appearance	Children are very similar, but there may be minor differences	Children can be completely different, even have different skin colors
Spiritual intimacy	Close all their lives, feel each other from a distance	Close enough	Some twins grow apart as they age
Probability of pregnancy	1 out of 3500-4000	An extremely rare occurrence	1 of 90

The medical explanation for mono- and dizygotic pregnancy completely answers the question of the difference between twins and twins. But no matter how many children are born, and no matter how similar they are, parents should raise individuals in their children.

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Identical twins or fraternal twins is something you hear when people talk about twins and twins. What does the number of eggs and twins have to do with it? We offer at the everyday level, without going deep into precise definitions, figure out what it is when people say fraternal or identical twins. We’ll also briefly touch on a couple more difficult points. Let’s connect “eggs” and zygotes plus pregnancy. We will deal with different and identical twins using everyday concepts and a school biology textbook.

Identical twins and fraternal twins - the basics

To better understand what fraternal or identical twins are
Let's remember some basics. Let's start with the fetus and multiple pregnancies.

Fetus- this is generally the result of pregnancy of the female body, in our case the mother. There are different stages of fetal development. Sometimes, based on these stages, the fetus is called an embryo or fetus. It's always about the same thing, about the result of pregnancy, i.e. about the fact that inside the mother’s body lives and develops, and then, in a positive result, should be born in the form of a child, in our case, twins.

Egg is a reproductive cell that develops in the female body. When merging with a male reproductive cell (sperm), the egg develops into a fetus through the process of splitting the egg into smaller other cells. The ovum is similar in structure and appearance to an egg, which is where it gets its name.

Multiple pregnancy

Pregnancy can be singleton or multiple
. Singleton - one child will be born, multiple pregnancy - two or more twin children may appear.

Twins(twins), triplets, etc. - these are numerical designations of the number of children born during a multiple pregnancy. Twins (twins) – two children, triplets – three, etc. However, they are all called twins, even if they were born in a different zodiac sign. They can also be identical or fraternal twins.

Twins- children born during one pregnancy and resulting from one birth to one mother. At the everyday level, everything is simple. Twins are different children from the same mother, after the same birth, and twins are identical children under the same circumstances. But in essence, it doesn’t matter whether they are similar or not, it doesn’t matter what they are called twins, twins or twins - they are still twins, you just need to remember. Twins are children born as a result of multiple pregnancy.

Identical and fraternal twins or twins

So, we know that children born as a result of multiple pregnancies can be identical or fraternal twins or, simply put, twins. And there is another option when the so-called mirror twins appear.

Identical twins (twins)

Identical twins or identical twins are children born as a result of multiple pregnancy when one egg is fertilized by one male reproductive cell, which leads to the appearance and development of two or more fetuses. The children turn out almost identical, i.e. identical.

How are identical twins made?

Let's outline how identical twins are created. In fact, any fertilized egg (it can be called a zygote) in the process intrauterine development divided into two or more parts. This is how children become genetic copies of each other, i.e. identical. Roughly speaking, this is how natural cloning occurs. It is to this process that we owe the appearance of twins.

The division of a fertilized egg is directly responsible for how identical twins are produced .

• If the division occurs before day 3, inclusive, after fertilization, then the result is dichorionic diamniotic twins, which is very similar to fraternal twins.
• If the division occurs between days 4 and 8 after fertilization, the result is monochorionic diamniotic twins.
• If on the 9th or 10th day - monochorionic monoamniotic twins.
• If between the 13th and 15th day, such separation will not be complete and the result will be monochorionic monoamniotic conjoined twins - Siamese twins.

What “chorial” and “amnion” mean will be discussed below.

Mirror twins are identical

By the way, identical twins can be mirror twins
, i.e. one of them has a location or appearance some objects of the body may be the same as if another looked in a mirror. For example, a mole on different parts of the body, one on the right, and the other on the left. One may be right-handed and the other left-handed. Identical mirror twins can only be monozygotic (homozygous) and occur in 25% of twin births. They may be very similar in fingerprints, but still differ in small details. Their blood type is the same.

Fraternal twins (twins)

Fraternal twins or twins are children born as a result of multiple pregnancy when two or more different eggs are fertilized by two or more different male reproductive cells, which also led to the appearance and development of two or more fetuses.

Simply put, each egg has its own sperm. Children can turn out different in everything. A striking example is twins, a boy and a girl, also known as royal twins. In this case, fraternal twins are always dichorionic diamniotic twins.

Identical twins and fraternal twins: "eggs" plus zygotes and pregnancy

Here we will actually make an attempt to combine medical, biological and everyday terms into one whole, so that we no longer get confused and understand exactly what we are being told about the same thing, just in different words. This is all about identical and fraternal twins.

All twins, twins, triplets, etc., as well as twins and twins, are twins in the biological sense. However, there are established terms and concepts in which the word “twins” is used.

In medical terminology, when describing pregnancy, twins are distinguished by the placenta (one or more) and by the number, presence of septa in one amniotic sac (one or more). There is a separate article on this subject: monochorionic diamniotic twins or monochorionic monoamniotic twins or diamniotic diamniotic twins - WHAT IS THIS or WHO IS THIS??? In it we tried to explain as simply as possible what it is. At first glance, it seems that this is a repetition of everything said above, and this seems correct. However, there are still those who are confused and think that it is all about different twins. It’s written there just for them, let them read it.

When describing the birth or appearance of twins, the differences between twins are described in the number of eggs involved in their appearance. There will also be words from the field of genetics - zygotes, genes, chromosomes.

At the everyday level, twins are always different, and twins are always the same, everything is simple here.

Fraternal twins = dizygotic twins = dichorionic diamniotic twins

Fraternal twins or twins are always and definitely dizygotic (heterozygous) and dichorionic diamniotic twins. These are twins in the everyday sense. Actually it's two different baby, in everyday life they would be called twins.

They were the result of a multiple pregnancy and will develop as two different children. The children will resemble each other like close relatives and nothing more. Here we started using “different” hetero, di and monozygotes. In the article monozygotic twins and dizygotic twins - WHAT IS IT, you can learn in detail about them and their connection with twins.

It should also be noted that, unlike identical twins, for fraternal twins it does not matter when the separation occurred, because it was the default at the time of conception. The only option is for the placentas to grow together. Then the dichorionic diamniotic twins “become similar” to the monochorionic diamniotic twins, but they are still two different placentas.

Identical twins = monozygotic twins

Identical twins or twins are always monozygotic, also known as homozygous twins, i.e. as a result of a multiple pregnancy, children of the same sex and blood type were absolutely similar to each other. In everyday life they are usually called twins. And then the differences begin, although at the everyday level they are still always twins. Identical twins (twins) are distinguished by:

• monochorionic diamniotic, i.e. fetuses (embryos) are connected in the womb to the mother by one placenta and each has its own amnion (amniotic sac). In fact, in the common amnion there is a partition separating the fetuses, and it turns out to be like their own apartment for each in a common house. Then identical twins, like fetuses, develop separately from each other. The probability of occurrence is 70-80% of all identical ones. Division occurred between 4 and 8 days after fertilization. If division occurs between the 13th and 15th day after fertilization, it will not be complete and the fruits (embryos) will grow together - a very difficult case.
• monochorionic monoamniotic, i.e. Fetuses share one placenta and one common amniotic sac. This means that the fruits are not separated by a septum in the amniotic sac, and develop together. This is a very dangerous option for the development of identical twins. There is a possibility of birth conjoined twins. Chance of occurrence is 1% of all identical ones. Division occurred after the 9th day, inclusive, after fertilization.
• dichorionic diamniotic, everything is like fraternal twins. The probability of occurrence is 20-30% of all identical ones. Division occurred up to 3 days, inclusive, after fertilization.