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How identical twins differ from fraternal twins. Fraternal twins. Signs of multiple pregnancy

Hello dear subscribers! Research shows that 15% of parents are misinformed about the chorionic nature of their twins. Often they are told that their identical twins are fraternal. This is not surprising, because sometimes even doctors do not understand the difference. I wanted to reveal in more detail the topic of identical twins interesting facts.

The fascination with the topic of twins in science was characteristic of late XIX- the beginning of the XX centuries. F. Galton studied and described them most fully. He developed the method that is still used in modern psychogenetics to determine the similarities and differences between mono- and dizygotic twins, the influence of genetic factors and the environment on their psychological qualities.

Scientists have found that identical twins have not only the same blood group, hair and eye color, but also similar mental capacity, personality traits, interests, a tendency toward optimism or depression.

The twin method predicts the birth of identical twins. If you are from dizygotic twins, then the chance of giving birth to two babies at the same time is 6%. Being from a monozygous couple, the chances are the same as for the rest - 1-2.5%. If one of the parents is an identical twin, this will not affect your chances of having twins.

What is the difference between identical and fraternal twins?

Identical or identical twins develop, which then mysteriously divided into two halves. Unlike raznoyatsevye, the likelihood of their occurrence does not depend on hereditary, geographic and other factors, and is 3 cases per 1000 births.
Determining their type is much more difficult than you might think. The medical concept is based on how they were conceived: from one egg or several, and how they developed in the uterus.

In the womb, babies are surrounded by two membranes:

  • internal called fetal bladder- forms a bag with amniotic fluid;
  • external, the so-called chorion - forms an additional layer around the amnion. The placenta grows from the chorionic tissue.

By carefully examining these membranes and the placenta (placenta) according to ultrasound data, the doctor can tell if the babies are identical. They can fall into one of the following categories:

  1. Dichorial diamniotic twins - Each child has its own placenta and separate outer and inner membranes. This applies to a third of identical and absolutely all fraternal twins. In the former, this happens if the fertilized egg divides in the first three days after conception. Despite the external similarity, you can distinguish between them.
  2. Monochorionic diamniotic - twins share one placenta and an outer membrane, but have their own amniotic sacs. This is how identical twins develop in two-thirds of cases, so this is the most common type. The egg cell splits in 4-7 days, and outwardly they will be very similar.
  3. Monochorionic monoamniotic - both babies have one placenta and one outer membrane. There is also one amniotic bladder, but without an inner dividing membrane. The division took place on days 8-12. They are extremely rare, only about 1% of all monozygous twins.

When to find out the type of twins?

It is possible to identify the type of twins being born during the first trimester. It is easiest to see if they have their own placentas and membranes between 10 and 13 weeks plus 6 days. Perhaps that's when you even know you're expecting twins.

How accurate is ultrasound for determining the type of twins?

An ultrasound scan, as a rule, quite accurately shows whether babies are sharing one placenta in two, especially if it is performed at 14 weeks. However, the ultrasound diagnostician may not be able to see everything accurately.

For example, when the placentas of fraternal twins merge and look like one single. In addition, some medical workers may think that identical babies cannot have two placentas. Although this is possible in dichorionic diamniotic twins.

Survey on later dates pregnancy when clearly visible gender may give some hints. Identical twins have the same genotype, so they are always of the same sex (although there are exceptions). On the other hand, you can have same-sex, mixed-egg babies. If you know for sure that, be sure - this is fraternal twins.

Why can identical twins be of different sexes?

This is possible with chromosomal abnormalities if one of the baby boys is no clear reason loses the Y chromosome and continues to develop as an XO girl (Turner Syndrome). Or in the case of semi-identical twins, when several spermatozoa fertilize one egg.

Should I be more careful about my pregnancy if I have identical twins?

Monochorionic twins are prone to more complications, since they have one placenta for two. If, moreover, they are monoamniotic, then the risks increase significantly, because their umbilical cords can become tangled. Your gynecologist will closely monitor the pregnancy of identical twins, prescribing various examinations and tests.


Most monochorionic babies are born completely healthy, but about 15% of them overtake a formidable complication called fetal fetal transfusion syndrome (FFT). This happens when there is an imbalance in blood flow - one twin gets too much circulating blood volume, and the other suffers from a lack of it. Untimely detection of SFT poses a great danger to the successful outcome of a twin pregnancy.

How to find out the type of twins after childbirth?

Sometimes it is impossible to know if they are identical when in the womb. Then you can find out immediately after their birth. However, just by looking at newborns it is difficult to tell. If babies are of the same sex and each has their own placenta, they may not be identical.

During the first year of life, other signs will indicate that they are identical:

  • eye color;
  • hair color and type;
  • arms, legs and ear shape;
  • coincidence of the time and order of teething.

Want to know the type of twins for sure? On help will come genetic testing of twins. For this, smears are taken by scraping. cotton swab on the inside of the cheek (buccal epithelium). identical twins in case positive result will match with 99.99% accuracy.

All good and see you!

Having multiple children during one pregnancy is a mystery that has not been fully solved even in the modern age of high technology. About one woman in a hundred has twins. Risk multiple pregnancy increases several times if the family already has twins.

Causes of multiple pregnancies

Why a woman instead of one child has two, and in rare cases even more, scientists do not know for sure. The impetus that prompts the body to form two eggs, or misdivide one, has never been identified.

Doctors lead the following reasons occurrence of multiple pregnancies:

Monozygous pregnancy

Monozygous pregnancy, in which identical twins develop, occurs when one egg is fertilized by one sperm, but its development fails and two embryos begin to develop. The factors that influence this division of the oocyte after fertilization have not been established. Also unknown dates, when two organisms appear from one cell. In the process of research, it was found that multiple pregnancies from one egg appear due to the division of the zygote.

Signs of identical twins:

There are several options for the development of a monozygous pregnancy:

  1. The zygote divides in the first days after conception. Because of this, embryos form each one for themselves. fetal bladder and the placenta. At the diagnostic stage, this form is often confused with fraternal twins.
  2. The zygote splits in the first week of conception. In this case, both embryos receive their amnions, but the placenta remains in common. This can cause the suppression of one child by another while still in the womb.
  3. The separation takes place after a week. These are very rare cases. With this flow, the embryos are in one fruit sac. This is considered dangerous: during pregnancy and childbirth, identical twins can become entangled in each other's umbilical cords or cause damage to each other.
  4. The separation takes place after two weeks. Two weeks after conception, the formation of the embryo begins. Separation at this stage leads to the appearance of fused embryos or Siamese twins... Most of them are not viable and have developmental defects. They usually die during development in the womb or at birth.

Heterozygous pregnancy

Heterozygous or fraternal babies appear when two embryos are conceived simultaneously in two different eggs. This type of pregnancy occurs most often. The formation of two eggs at once in one menstrual cycle may be due to external and internal factors: when receiving hormonal drugs, with IVF and with hereditary predisposition.

Signs of a heterozygous pregnancy:

The probability of pregnancy is quite high: one in a hundred. When heterozygous, conception occurs in two eggs, which are secreted from two ovaries at the same time. Such embryos have their own amniotic sacs, placenta and umbilical cords. Fraternal twins develop separately and have little or no influence from one to one.

Monozygous polar pregnancy

Polar monozygotic twins are extremely rare. In this case, pregnancy occurs due to the fertilization of the egg and its polar body. During conception, two sperm cells enter the cell at once. The rarity of such monozygotic twins is due to the fact that embryos die on early dates In most cases.

Signs of polar monozygotic twins:

  • children are quite similar, but may have some differences in appearance;
  • characters may coincide, but aspirations, hobbies, ideals differ;
  • children may have a different blood group;
  • v future life children feel closeness and are good friends.

Features of the course of multiple pregnancy

A woman is at greater risk during multiple pregnancies than when carrying a single child.

There are the following possible pathologies when carrying multiple embryos:

  1. Violation of blood flow during monozygotic pregnancy, when one of the twins may develop hypoxia due to a lack of blood.
  2. The absence of one or more organs, body parts in one of the twins.
  3. The death of one of the fruits.
  4. Chromosomal abnormalities.
  5. Development pathologies.

Multiple pregnancies must be carried out under the supervision of a gynecologist. A week before the expected birth, expectant mother placed in the maternity ward. If the number of children is not more than two and they do not have pathologies, natural delivery is allowed, in other cases a cesarean section is performed.

There is no unambiguous hypothesis for the formation of identical twins. Obviously, most often the occurrence of identical twins (triplets, etc.) is associated with the fertilization of an egg, which has two or more nuclei. Each nucleus connects with the nuclear substance of the sperm and the embryo is formed. Eggs with two and three nuclei were identified. There is also another mechanism for the origin of identical twins: a single embryonic primordium in the cleavage stage is divided into two parts, from each part a fetus is formed.

During separation before the formation of the inner layer (in the morula stage) and the transformation of the outer layer of the blastocyst cells into chorionic elements, which occurs in the first 72 hours after fertilization, two amniotic sacs and two chorions develop. The result is biamniotic bichorial monozygotic twins.

If the separation occurs on the 4-8th day after fertilization, at the end of the formation of the inner layer of the cetokas and the laying of the chorion from the outer layer, but before the laying of the amniotic cells, that is, before the appearance of the fetal bladder, two embryos are formed, each in a separate amniotic sac - develops monochorial biamniotic monozygous twins. Most monozygotic twins (70-80%) are represented by this type.

If by the time of separation the amnion has already been laid, which occurs on the 9-12th day after fertilization, then the separation leads to the formation of two embryos in one amniotic sac, that is, monochorial monoamniotic monozygous twins. It is the rarest type of monozygotic twins, and occurs in approximately 1% of monozygotic twins. However, there is a significant risk in terms of the course of pregnancy.

After the 15th day, complete separation of the embryonic primordia is not possible. In this case, conjoined twins develop. This type is quite rare, about 1 in 1500 many fetal pregnancies.

Identical twins are always same-sex, have the same blood group, the same color of eyes, hair, skin relief of the fingertips, the shape and position of the teeth, and are very similar to each other. They tend to have the same diseases at the same time and have the same learning abilities.

In monochorionic biamniotic monozygotic twins, the membrane that separates the two amniotic cavity, rather transparent, it has no vessels, as well as the remains of the decidua and trophoblast. At the same time, in one degree or another, there is always certain type Feto systems connections placental circulation twins, which contributes to the development of transfusion syndrome.

It should be noted that in monochorionic placentas, a vascular anastomosis can be found quite often - arterioarterial or arteriovenous, which causes the development of fetofetal transfusion syndrome. The arteriovenous connection is made through the capillary system of the placenta. As a result of this anastomosis, blood flows from an artery to a vein from one fetus to another. In bichorionic placentas, arteriovenous anastomosis develops much less frequently. The consequences of such an anastomosis can be very serious. If in vascular system placenta blood pressure symmetrically, both twins find themselves in the same habitat and development. However, with identical twins, this balance can be disturbed due to asymmetric placental circulation, and then one fetus receives more blood (recipient) than the other (donor). The latter does not receive sufficient nutrition and finds itself in worse conditions for its development, which can cause delay intrauterine development of the fetus, With a sharp imbalance in the placental circulation system, one of the twins (donor) is gradually depleted, dies and mummifies, turning into a "paper fetus" (fetus papyraceus). Often, the recipient twin develops polyhydramnios and dropsy due to heart failure.

Fraternal twins

Among all types of twins, twins are observed in 70% of cases.

The formation of double doubles is possible in the case of:

  • simultaneous maturation and ovulation of two or more follicles in one ovary;
  • maturation and ovulation of two or more follicles in both ovaries,
  • fertilization of two or more eggs that have matured in one follicle.

Such variants of the origin of fraternal twins are evidenced by the identification of surgical interventions two or more yellow bodies the same age in one or both ovaries.

Dizygotic twins are always characterized by a bichorial, biamniotic type of placentation. That said, there will always be two autonomous placentas that can fit snugly but can be separated. Each fertilized egg that enters the decidua forms its own amniotic and chorionic membranes, from which its own placenta is subsequently formed. If the eggs have penetrated into the decidua close to one another, then the edges of both placentas are closely adjacent, which gives the impression of a single formation. In fact, each placenga has its own vascular network, each fetal sac has its own amniotic and chorionic membranes. The partition between the two fetal sacs consists of four membranes: two amniotic and two chorionic, and the decidua is common (bichorionic twins). If the fertilized eggs have penetrated a considerable distance, then the placentas develop as separate formations, and each fertilized egg has its own, separate decidua.

Fraternal twins can be either same or opposite sex and share the same genetic dependency as siblings.

The difference in body weight in fraternal twins is usually small and ranges from 200-300 g. individual cases due to different conditions intrauterine nutrition, the difference can be quite significant - up to 1 kg and even more.

The birth of a long-awaited child in a family is always a joy. And if two or more babies are born at once, happiness increases in direct proportion to their number.

Let's talk about the factors that contribute to the development of multiple pregnancies, as well as the differences between identical and fraternal twins.

Who are considered twins?

It is customary to call twins children who were born as a result of one pregnancy. Moreover, they can be either the same or different sex. Despite the fact that there are two concepts among the people: twins and twins, medicine recognizes only the first name. But it divides it into two types: identical and different.

Parents-to-be need to know about some of the nuances of multiple pregnancies.

Firstly, in any case, children will be cramped in the womb. Therefore, it often happens that one of them lacks placental nutrition. In addition, these babies are usually underweight and may be lagging behind. physical development from their peers. A little later they begin to hold their heads, sit, crawl, walk, and so on.

Secondly, the birth of twins is not only a double joy, but also an increase in the number of worries. After all, both babies need to be fed, changed, bathed, and so on in the same way.

As for the pluses, they include the early social development such kids. They learn to communicate with each other earlier than their peers. By the age of 10 months they are developing friendly relations, they are capable of feeling jealous if their parents are busy with their brother or sister. The twins are already before one year old they know how to get upset when they do not see each other and begin to get bored.

Identical twins

If a fertilized cell is divided into several parts, each of which continues to develop separately, each of the embryos will receive the same set of genes. It is in this way that conception occurs.Such babies usually develop at about the same pace, they are always of the same sex and are very similar in appearance. Although there are times when children have mirror features. For example, one of them may have a and the other on the left, and so on. In addition to all this, identical twins usually have similar temperaments and characters, have the same interests.

For illustrative example of what identical twins look like, provided the photo below.

For normal pregnancy the division of the egg into several parts is not characteristic, therefore, cases of the birth of monozygotic twins are not so common.

Fraternal twins

It is they who are popularly called "twins". Why are fraternal twins born? The reasons for this type are that several eggs are fertilized at the same time. Moreover, each of the embryos develops independently, and future children can be of the same or different sex. To have an understanding of what fraternal twins look like, take a look at the photo below, it will serve as an example.

As you can see, the similarities between them are the same as those of ordinary brothers and sisters.

They also differ in temperament, interests, character traits.

As a woman ages, the likelihood of multiple pregnancies increases. Although the birth of fraternal twins is primarily associated with a genetic predisposition.

Gemini identical and different: what are the differences

Summing up the above and adding new information to this, we can highlight general differences between identical and fraternal twins.

  1. A method of fertilization, which occurs as a result of the division of one or the simultaneous fertilization of several eggs.
  2. In the womb, fraternal twins each have their own placenta and amniotic fluid... For identical ones, they can be either different, or one for two.
  3. Appearance. Identical twins are often like two peas in a pod, and in some cases even their parents cannot distinguish between them. Fraternal possess different looks, and similarities are only possible as between ordinary siblings. They may even have different hair color, face shape, blood type and its Rh factor.
  4. Character. Identical twins are usually similar even in demeanor and preferences, while fraternal twins develop completely differently and can be complete opposites of each other.

What contributes to the birth of twins?

Why does it happen that in one family there may even be several pairs of twins, and in another, children are born exclusively one at a time? There are several predisposing factors due to which identical and fraternal twins are born. In each of the cases, they are different, therefore, we will consider them separately from each other.

The birth of identical twins is facilitated by:

  • the presence of oxygen deficiency;
  • exposure to toxic factors on a pregnant woman;
  • the woman is over 30 years old.

Fraternal twins can be born if one or more of the following factors are present:

  • taking hormonal contraceptives for a long period of time or canceling them;
  • hereditary predisposition;
  • abnormalities in the development of the uterus;
  • stimulation of ovulation.

In addition to all this, there is a relationship between multiple pregnancies and race. As statistics show, African women have a much higher chance of getting pregnant with twins than Asian women.

Signs of multiple pregnancy

How to determine that identical or fraternal twins will soon be born in a family? Most the exact way is, of course, holding ultrasound examination(Ultrasound). In addition, multiple pregnancies can be judged by too rapid increase the uterus and the discrepancy between its size and the term. Such information can be obtained from a gynecologist, who always pays attention to this during a mandatory examination.

Another point is the presence big belly already in the early stages. Not always, but in many cases, this also indicates that several babies will be born at the same time.

Easy pregnancy!

Cases when not one, but two or more babies settle in the mother's stomach, are not so common - 1.5-2.5% of all pregnancies. How does it work? What is the difference between multiple pregnancies? Can twins be scheduled? Our expert, Anna Romanovna PASTUKHOVA, obstetrician-gynecologist of the Zdravitsa family medicine centers, answers all questions.

What is the likelihood of getting pregnant with twins?

First, some statistics. As we have already mentioned, this amazing phenomenon occurs in 1.5-2.5% of pregnancy observations 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, among which .

  • The birth of twins occurs with a frequency of geometric progression, obstetricians even have a special formula: for 87 births there is one twins, for 87 twins - one triplet, for 87 triplets - one quadruple, etc. True, today this formula needs correction - multiple pregnancies are becoming more common.
  • Identical or identical twins are less common: an average of 1 case per 250 births.
  • Most often, multiple pregnancies are observed in Africa, least often in Asian countries.

Types of multiple pregnancies

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

  • Monozygous twins result from the division of one egg, fertilized by one sperm. They surprise everyone with their striking resemblance.
  • Fraternal twins are the result of the fertilization of multiple eggs with multiple sperm. They can be either of the same sex or of different sex, often differ in character and are not always similar in appearance.

Expert commentary

Multiple pregnancy is a pregnancy when more than one fetus develops in the mother's body, but several at once. In medicine, there are identical or fraternal twins (triplets and so on). Identical twins are always the same sex, have the same blood type, and are very similar in appearance. Fraternal twins have phenotypic differences (eye color, facial features), it can be either the same or different group blood. Fraternal twins can be heterosexual.

How identical twins are made

To be honest, we have no idea! The reasons why, instead of a single baby from one egg and one sperm, two (three, four) appear are not really known - a miracle, and nothing more. The mechanism of the emergence of monozygotic twins, however, is described in sufficient detail. It all starts 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 begins to live a life of its own.

Expert commentary

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

Are the twins interfering with each other?

It is very important at what point the egg cell splits, since further intrauterine development twins.

There are 3 options for the development of monozygotic twins

  • The separation of the ovum 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 such a development is characteristic only of fraternal twins and identical twins in such cases were mistakenly identified as dizygotic (maybe this happened with the Olsen sisters?)
  • The zygote split approximately 5-8 days after fertilization. By this time, the external fetal membrane has already begun to form: remains common in babies, however, the inner fetal membrane (amnion) develops in each individual. If babies have a common placenta, then one child can suppress another - their competition begins with conception.
  • Separation occurred on day 8 or later (1% of all monozygotic twins). At this time, the fetal bladder is already beginning to form, so the divided embryos will grow in the common amnion and common fruit waters... This situation is considered not the most favorable, there is a risk that babies each other.

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

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

Expert commentary

Distinguish the following types multiple pregnancy:

  • 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 bladder
  • Dichorial diamniotic twins, when each fetus has its own placenta and its own amniotic bladder.

How fraternal twins are made

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 stimulation ovaries, the first cycle after the abolition of hormonal contraceptives.

Do you know that....

  • The difference in time of conception of fraternal twins can be from several hours to several days.
  • In very rare cases, already existing pregnancy added ... new. As a rule, after fertilization and implantation of the ovum, ovulation is immediately blocked. If due to hormonal imbalance this mechanism does not work immediately, it is added to the older child in utero younger brother or sister.