How are fraternal twins different? Fraternal and identical twins: differences

Hello dear subscribers! Studies show that 15% of parents are misinformed about the chorionality of their twins. They are often 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 typical in the late 19th and early 20th 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 not only have the same blood type, hair and eye color, but also similar mental abilities, personality traits, interests, a tendency to optimism or depression.

The twin method allows you to predict 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 monozygotic couple, the chances are the same as for the rest - 1-2.5%. If one of the parents is an identical twin, then 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 splits into two halves. Unlike fraternal, the probability of their occurrence does not depend on hereditary, geographical 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 the fetal bladder - forms a bag with amniotic fluid;
• outer, the so-called chorion - forms an additional layer around the amnion. The placenta grows from the tissues of the chorion.

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

1. Dichorionic diamniotic twins - each baby has its own placenta and a separate outer and inner membrane. This applies to a third of identical and absolutely all fraternal twins. In the first, this happens if the fertilized egg is divided in the first three days after conception. Despite the external similarity, they can be distinguished.
2. Monochorionic diamniotic twins share the same placenta and outer membrane but have their own amniotic sacs. This is the development of identical twins in two-thirds of cases, so this is the most common type. The egg splits on days 4-7, and outwardly they will be very similar.
3. Monochorionic monoamniotic - both children have one placenta and one outer membrane. There is also a single amniotic sac, but without an internal separating membrane. Separation occurred on days 8-12. They are extremely rare, only about 1% of all monozygotic twins.

When to find out the type of twins?

You can identify the type of twins you are carrying during the first trimester. It is easiest to see if they have their own placentas and membranes at 10 to 13 weeks plus 6 days. Perhaps that is when you will even know that you are expecting twins.

How accurate are ultrasounds for determining the type of twins?

An ultrasound is usually quite accurate in showing whether babies share one placenta for two, especially if it is performed at 14 weeks. However, an ultrasound diagnostician may not be able to see everything accurately.

For example, when the placentas of fraternal twins merge and look like one single placenta. In addition, some health professionals may feel that two placentas cannot be identical babies. Although this is possible in dichorionic diamniotic twins.

Examination late in pregnancy, when gender is clearly visible, may provide some clues. 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 fraternal 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, for some unknown reason, loses the Y chromosome and continues to develop as a girl with the XO chromosome (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 more prone to complications because they share the same placenta. If, in addition, 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 children are born absolutely healthy, but about 15% of them are overtaken by a formidable complication called feto-fetal transfusion syndrome (FFTS). This happens when there is an imbalance in blood flow - one twin receives too much circulating blood, and the other suffers from a lack of it. Untimely detection of SFFT is a great danger for 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 they are in the womb. Then you can find out immediately after their birth. However, just by looking at newborns, it's hard to tell. If babies are of the same sex and each have 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 timing and order of teething.

Want to know the type of twins for sure? Genetic testing of twins will come to the rescue. To do this, smears are taken by scraping with a cotton swab from the inside of the cheek (buccal epithelium). identical twins in case of a positive result will match with an accuracy of 99.99%.

All the best and see you soon!

The birth of twins, in itself, is a rare phenomenon. According to statistics, only 2% of all children born are twins. At the same time, the birth of three children at once is observed even less frequently. This happens only in 2% of all twins born.

At the same time, it should be noted that it can be different, and far from always born babies have an external resemblance. So from a genetic point of view, twins can be fraternal (fraternal) and identical.

How are fraternal twins made?

Fraternal twins are born as a result of the fertilization of 2 mature eggs at once. Moreover, despite the fact that their development in the uterus occurs simultaneously, the difference in the time of conception can sometimes be several hours.

The sex of such babies can be either the same or different. Each fetus has its own placenta, independent circulatory system, and its own amniotic membrane. The only thing that unites them is the uterus in which they develop.

Thus, the main difference between fraternal and identical twins is that 2 embryos develop from 2 separate eggs, which are fertilized by different spermatozoa. The development of identical twins occurs from one fertilized egg, as a result of its division at the initial stage of pregnancy.

What is the probability of having fraternal twins?

Of paramount importance in this case is the age of the expectant mother. So, it was found that with age, the onset of multiple pregnancy increases. From a medical point of view, this fact is explained by the fact that with an increase in the number of years lived in a woman, more hormones are produced in the body, in particular those that stimulate the maturation of eggs. Thus, it is not uncommon for several mature eggs to come out of the follicles during ovulation. That is why at the age of 35-38 there is a high probability of multiple pregnancy.

In addition, heredity plays an important role in this matter. So, if the family already has twins, then the probability of giving birth to another pair is quite high, but it decreases with the distance in time of the generation of twins. At the same time, the ability to conceive twins is transmitted only through the female line. Men can pass it on to their daughters, but there is no noticeable frequency of twins in the offspring of men themselves.

The birth of twins is one of the most amazing natural phenomena. Gemini cause admiration and constant interest in others.

From time immemorial, people have worshiped twins, like a deity. The stars and constellations were named in their honor (twin brothers Pollux and Castor, children of Zeus), their names are immortalized on the coat of arms of Rome (twins Romulus and Remus). The ancients considered the twins to be chosen and endowed them with special privileges. And today the birth of twins is a small miracle.

How is the conception of twins

Twins are considered to be several children (twins, triplets, and so on), simultaneously born to one mother. The bearing of several children by a pregnant woman is called a multiple pregnancy.

It occurs if:

• an egg fertilized by a spermatozoon - a zygote - splits into two or more parts;
• the egg has two or more nuclei and is fertilized by several spermatozoa;
• two or more eggs are fertilized.

Identical and fraternal twins

Twins are divided into identical (monozygotic) and fraternal (dizygotic). The first are completely identical, having the same genotypes. The zygote splits into genetically identical symmetrical halves, with the same hereditary potential, but developing as two independent individuals.

Such twins are always of the same sex, with the same blood type, with the same signs of physical structure. Identical twins have the same eye color, hair, the same shape of the lips. These people have the same fingerprints.

Fraternal twins have a high percentage of similarity in lip shape (60%), eye color (30%) and hair color (20%), although their genotypes are 50% the same. When fraternal twins are conceived, two or more eggs are simultaneously fertilized by two or more sperm.

The conception of fraternal twins occurs when two or more eggs are almost simultaneously released from the ovary, breaking the follicles. This process can take place both in both ovaries, and in one (which happens more often).

Subsequently, the fertilized eggs begin to divide, move along the fallopian tube and enter the uterine mucosa. Here they develop separately from each other, equipped with separate.

What affects the conception of twins

According to statistics, for every hundred births there is an average of one birth of twins. Approximately two thirds of them are fraternal (developing from two different eggs with simultaneous fertilization by two different spermatozoa), one third are identical twins. For every 104 pairs of male twins, 100 pairs of female twins are born.

Without a doubt, twin pregnancy, or otherwise multiple pregnancy, is genetically determined. Currently, the factors affecting the frequency of twin births are far from being fully understood. But some regularities can be spoken with full confidence.

Woman's age

Identical twins can be born in women of any age, but fraternal twins are more often born in women 35-45 years old. This is due to the hormonal changes in the female body that occur at this age. Late-birth mothers are several times more likely to have twins again.

Race

Race is one of the determining factors for conceiving twins. So, black mothers have twins much more often. But among representatives of the Mongoloid race (for example, the Japanese), the birth of twins is an extremely rare phenomenon.

hereditary factor

An important role in the appearance of fraternal twins is played by the factor of heredity (more often along the mother's side). Some women have the possibility of several ovulations in one menstrual cycle, the so-called natural multiple ovulation.

A woman's ability to multiple ovulation increases her chance of conceiving twins tenfold.

If a woman or her husband is from twins, if any of the relatives have already had a multiple (twin) pregnancy, then the chance that the children of such parents will be twins is very high. The probability of multiple pregnancy in one generation increases even more.

The medicine

The probability of conceiving twins increases many times if a woman, for any medical reasons, took drugs that stimulate the ovaries (for example, in the treatment of infertility). Hormone therapy in this case stimulates the maturation of two or more eggs.

Probable multiple (twin) pregnancy and artificial insemination. Up to six embryos artificially fertilized in a test tube can be introduced into a woman's uterus.

When can I find out about the conception of twins

It is possible to determine that twins have been conceived already in the third or fourth month of pregnancy using ultrasound (ultrasound). From the sixth month of pregnancy, with the help of an electrocardiogram, you can hear the beats of several hearts.

The sooner a multiple pregnancy is detected, the better for the expectant mother. In this case, the pregnant woman should be under special medical supervision.

The conception of twins is a happy gift of fate, and the twins that are born are maternal happiness, multiplied several times.

The appearance of twins is about 1.5% of all newborns. Modern medicine still cannot say exactly why this happens. It is known that the hereditary factor plays a role, for example, 31 women out of 300 had multiple pregnancies in relatives. In addition, the likelihood increases after the abolition of hormonal contraceptives, which have been taken for a long time.

What are twins?

Twins can be identical or fraternal. When, at the very first stage of pregnancy, a fertilized egg is divided into two or more parts, each of which is formed as an independent organism, identical twins, or monozygotic twins, are born.

They are always of the same sex, very similar in appearance, have the same set of genes, often suffer from the same diseases at the same time.

Fraternal twins, or twins, as they are popularly called, develop not from one, but from two eggs that have simultaneously matured in the ovary (ovaries), and at the same time each of them is fertilized by different spermatozoa. Such children are different, like ordinary brothers and sisters born at different times. The genetic structure of these children is completely different.

They can have different blood types and gender, facial features and character. The main difference between fraternal and identical twins is that their genetic similarity is 40-60%, that is, like ordinary brothers and sisters.

Cases of so-called Siamese twins are also widely known. For the first time this phenomenon was stated in Siam (Thailand) at the end of the 19th century. Siamese twins develop from one egg that began dividing at a later date. As a result, the division is incomplete.

Causes of multiple pregnancy

In addition to hereditary predisposition and hormonal drugs, there are several other factors that increase the chances of having multiple children:

• Identical twins can be born due to increased production of a hormone that stimulates the maturation and development of eggs;
• In women from 35 to 39 years old, the chances of having twins also increase. This is explained by the fact that a kind of hormonal surge occurs before menopause, so late pregnancies are quite often multiple;
• Not to mention IVF - in vitro fertilization. According to statistics, often women after IVF have several children at a time. This phenomenon is due to the use of drugs for the treatment of infertility.

Diagnosis of multiple pregnancy

This fact can be established already in the first trimester: the size of the uterus significantly exceeds the norm with a singleton. By the end of the third month, this becomes even more noticeable. You can confirm the assumption with the help of ultrasound. It also happens that for the first time two fetal eggs were found, but at the next planned study, only one. This happens when one of them dies.

With the help of ultrasound, specialists should establish the identity of the fetus - identical or fraternal twins, as well as chorionicity (the number of placentas). The study should be carried out up to a maximum of 14 weeks, since on the basis of the data obtained, the observing doctor draws up a pregnancy management plan.

Also, timely detection of complications characteristic of monochorionic twins depends on this information. For example, feto-fetal transfusion syndrome may occur. In addition, you will need to choose the option of delivery.

The results of the trinity test are not taken into account. The development and condition of the fetus is judged by the indicators of alpha-fetoprotein, chorionic gonadotropin and placental lactogen. These data allow to identify defects and chromosomal pathologies. But with multiple pregnancy, regardless of the number of placentas, much more of these substances are produced.

Multiple pregnancy: features of the course

This phenomenon requires increased attention, since the woman's body is designed to carry and feed one baby. Therefore, twins during pregnancy fall into the so-called biological risk group. In the first trimester, there is a high probability of the death of one of the fetal eggs.

Due to an increase in erythropoiesis in the second half of pregnancy, depletion of iron stores is possible, which provokes anemia. To monitor the condition of the woman and the fetus, a blood smear test is performed.

In a woman, the diaphragm is significantly displaced, the work of the heart and lungs is difficult, there is increased fatigue and shortness of breath, frequent urge to urinate and constipation. Toxicosis, varicose veins also often occur.

In this case, the threat of premature birth or miscarriage in the second and third trimester may develop.

The main reason is excessive stretching of the muscles of the uterus due to the large volume, which provokes labor. Therefore, often women with twins are prescribed drugs to relax the uterus.

To reduce the risk of preterm birth, control the condition of the cervix. If it is shortened, stitches are applied or a pessary is installed.

The bearing of twins is often accompanied by an incorrect position and presentation of the fetus, for example, pelvic, transverse. This factor is decisive in choosing the method of delivery.

To monitor the condition and development of the fetuses, dynamic fetometry and doplerometry are used. It is worth noting that twins can grow differently, for example, one may lag behind in development.

Also, women with multiple pregnancies are more likely to suffer from urinary tract infections. This is due to a violation of the normal outflow of urine and the position of the internal organs due to a significantly enlarged uterus. Such expectant mothers need more careful clinical and laboratory monitoring.

Attention is not bypassed and the weight of the pregnant woman. The difference is that with a singleton pregnancy, the norm is 9-15 kg, but in the case of twins, body weight can increase by another 20 kg. A woman's diet should be balanced, but not high in calories. In the event of edema, the amount of fluid per day is reduced to 1.5 liters.

childbirth process

A woman with twins goes to the maternity hospital a few weeks before the expected date of birth. As a rule, childbirth occurs at 36-37 weeks. The most favorable period for twins is 36-38 weeks, for triplets - 34-36.

The birth process itself can occur naturally. Not always with multiple pregnancies, a caesarean section is prescribed. However, some complications may occur in the process: untimely discharge of water, prolapse of part of the umbilical cord, arms / legs of the fetus.

The birth of several children during one pregnancy is a mystery that is not completely solved even in the modern age of high technology. Approximately 1 in 100 women have twins. The risk of multiple pregnancy increases several times if the family already has twins.

Reasons for multiple pregnancy

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

Doctors give the following reasons occurrence of multiple pregnancy:

Monozygotic pregnancy

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

Signs of identical twins:

There are several options for the development of monozygotic pregnancy:

1. The zygote divides in the first days after conception. Because of this, the embryos form each for themselves a fetal bladder and a placenta. This form at the diagnostic stage is often confused with fraternal twins.
2. The zygote divides in the first week of conception. In this case, both embryos receive their amnions, but their placenta remains common. This can cause one child to be suppressed by another while still in the womb.
3. Separation occurs later than a week. These are very rare cases. With this flow, the embryos are in the same 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. Separation occurs after two weeks. Two weeks after conception, the formation of the embryo begins. Separation at this stage results in conjoined embryos or Siamese twins. Most of them are not viable and have malformations. As a rule, they die during development in the womb or at birth.

heterozygous pregnancy

Heterozygous or fraternal babies appear if there is a simultaneous conception of two embryos in two different eggs. This is the most common pregnancy. The formation of two eggs at once in one menstrual cycle can occur due to external and internal factors: when taking hormonal drugs, with IVF and with hereditary predisposition.

Signs of heterozygous pregnancy:

The probability of pregnancy is quite high: one in a hundred. With heterozygous conception occurs in two eggs, which are released 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 to no effect on one another.

Monozygotic polar pregnancy

Polar monozygotic twins are extremely rare. In this case, pregnancy occurs due to the fertilization of the egg and its polar body. At conception, two spermatozoa enter the cell at once. The rarity of the occurrence of such monozygotic twins is due to the fact that embryos die early 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 type;
• in the future life, children feel closeness and good friends.

Features of the course of multiple pregnancy

During multiple pregnancy, a woman has a greater risk than during the bearing of one 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 begin hypoxia due to 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 disorders.
5. developmental pathology.

Multiple pregnancy must be carried out under the supervision of a gynecologist. A week before the expected birth, the expectant mother is 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 caesarean section is performed.