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 several eggs mature in a woman’s body in one cycle. 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.

The birth of twins is one of the most amazing natural phenomena. Geminis arouse admiration and constant interest among others.

From time immemorial, people have worshiped twins like a deity. 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 twins to be the chosen ones and gave them special privileges. And today the birth of twins is a small miracle.

How twins are conceived

Twins are considered to be several children (twins, triplets, etc.) born at the same time to the same mother. When a pregnant woman carries multiple children, it is called a multiple pregnancy.

It occurs if:

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

Identical and fraternal twins

Twins are divided into identical (monozygotic) and fraternal (dizygotic). The first ones 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, and with the same physical characteristics. Identical twins have the same eye color, hair color, and lip shape. Such 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 released from the ovary almost simultaneously, rupturing the follicles. This process can occur in both ovaries, or in one (which happens more often).

Subsequently, the fertilized eggs begin to divide, move through 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. About two-thirds of them are fraternal twins (developing from two different eggs when fertilized simultaneously by two different sperm), one third are identical twins. For every 104 pairs of boy twins, 100 pairs of girl twins are born.

Without a doubt, twin pregnancy, or otherwise multiple pregnancy, is genetically determined. Currently, the factors influencing the incidence of twin births are far from fully understood. But we can talk about some patterns with complete confidence.

Woman's age

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

Race

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

Hereditary factor

A major role in the occurrence of fraternal twins is played by the factor of heredity (usually through the mother’s side). For some women, it is possible to have several ovulations in one menstrual cycle, so-called natural multiple ovulation.

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

If a woman or her husband is a twin, if a multiple (twin) pregnancy has already occurred in one of the relatives, then the chance that the children of such parents will be twins is very high. The likelihood of multiple pregnancies within one generation increases even more.

Medicine

The likelihood of conceiving twins increases many times over if a woman, for some medical reason, has taken medications that stimulate the ovaries (for example, in the treatment of infertility). In this case, hormonal therapy stimulates the maturation of two or more eggs.

Multiple (twin) pregnancies are also possible with artificial insemination. Up to six embryos, artificially fertilized in a test tube, can be introduced into a woman's uterus.

When can you find out about conceiving twins?

It is possible to determine that twins have been conceived already in the third or fourth month of pregnancy using an ultrasound examination (ultrasound). From the sixth month of pregnancy, several heartbeats can be heard using an electrocardiogram.

The earlier 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 birth of twins is a mother's happiness, multiplied several times.

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

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, are born.

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

Fraternal twins, or fraternal twins, as they are popularly called, develop from not one, but two eggs that mature simultaneously in the ovary(s), and each of them is fertilized by different sperm. Such children are different, like ordinary brothers and sisters born at different times. The genetic structure of such children is completely different.

They may have different blood types and genders, 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.

There are also widely known cases of so-called Siamese twins. This phenomenon was first noted in Siam (Thailand) at the end of the 19th century. Siamese twins develop from one egg, which begins dividing at a later date. As a result, the division is incomplete.

Causes of multiple births

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;
• Women aged 35 to 39 also have an increased chance of having twins. This is explained by the fact that before menopause there is a kind of hormonal surge, so late pregnancies are quite often multiple;
• It is impossible not to mention IVF - in vitro fertilization. According to statistics, it is not uncommon for women after IVF to have several children at a time. This phenomenon is caused by 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 for a singleton. By the end of the third month this becomes even more noticeable. This assumption can be confirmed using ultrasound. It also happens that the first time two fertilized eggs were discovered, but at the next planned examination only one. This happens when one of them dies.

Using ultrasound, specialists must determine the identity of the fetuses - 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 based on the data obtained, the supervising doctor draws up a pregnancy management plan.

Also, the 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 a delivery option.

The results of the trigeminal test are not taken into account. The development and condition of the fetus is judged by the indicators of alpha-fetoprotein, human chorionic gonadotropin and placental lactogen. These data make it possible to identify defects and chromosomal pathologies. But with multiple births, 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 a woman’s body is designed to bear and feed one baby. Therefore, even during pregnancy, twins fall into the so-called biological risk group. In the first trimester, there is a high probability that one of the fertilized eggs will die.

Due to an increase in erythropoiesis in the second half of pregnancy, iron reserves may be depleted, which provokes anemia. To monitor the condition of the woman and the fetus, blood smears are examined.

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

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

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

To reduce the risk of premature birth, the condition of the cervix is ​​monitored. If it shortens, stitches are placed or a pessary is installed.

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

To monitor the condition and development of the fetus, dynamic fetometry and Dopplerometry are used. It is worth noting that twins may grow differently, for example, one may be developmentally delayed.

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

The weight of a pregnant woman is also not ignored. The difference is that in 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. If edema occurs, the amount of fluid per day is reduced to 1.5 liters.

Childbirth process

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

The birth process itself can occur naturally. A cesarean section is not always prescribed for multiple births. However, some complications may arise in the process: untimely release of water, loss of part of the umbilical cord, or the arms/legs of the fetus.

Sometimes there are weak contractions and straining due to overstretching of the uterus, fetal hypoxia, postpartum hemorrhage, premature placental abruption of the second placenta after the first child passes through the birth canal.

But twin children have a higher ability to adapt. Their lungs develop and mature earlier than others, which allows them to breathe independently even at an early birth. At the same time, identical twins differ from fraternal twins in the early postpartum period: they adapt less well to changes in living conditions.

In addition, they are more likely to develop pathologies associated with respiratory distress, and they are also more prone to icteric and edematous syndrome. Enjoy your pregnancy, easy birth and health to your twins!

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Babies born to a mother from the same pregnancy are called twins or twins. Such children always arouse the interest of others and this is not at all surprising, since twins are born much less frequently compared to singleton pregnancies. It’s not enough to just say “twins”, depending on how they came into being, there are identical or fraternal twins.

Who are identical twins?

Identical twins are those babies who were born as a result of the splitting of one fertilized egg at a certain stage of embryogenesis. No one can say why this happens, but such babies can be born to any woman, regardless of genetic predisposition to multiple births, race, or age. Predisposing factors to the bifurcation of the zygote during its development are:

• hormonal imbalance in a woman’s body;
• retention of the zygote in the fallopian tubes for any reason;
• a woman taking certain medications before pregnancy;
• insufficient nutrition of pelvic tissues with oxygen and nutrients.

Mirror Twins

Identical twins have an absolutely identical genotype and are very similar to each other, sometimes it is difficult for their parents to distinguish them. About ¼ of identical twins are mirror twins, meaning they have moles or birthmarks in the same places, the same shape and the same size.

Gender of identical twins

Since identical babies are born as a result of the splitting of one fertilized egg, they will definitely be of the same age, which is determined already at the moment of the fusion of the sex cells of the mother and father.

Identical twins with different chorions

The presence of common or own membranes in identical twins depends on the exact stage of embryogenesis at which the zygote split. If the separation occurred on days 5-7, that is, at the morula stage of development, then the twins will have different chorions, representing the future placenta. When the zygote is separated up to 5 days, the fetuses have one common placenta, which is what occurs most often with this type of twins.

What causes differences in identical twins?

It is believed that the later the zygote splits in identical twins, the more similar the children will be to each other, and vice versa, if the separation of the fertilized egg occurs on the very first days of embryogenesis, then the children will simply be very similar to each other, but parents will easily distinguish them . Despite this, identical twins will always be the same sex, regardless of the day the zygote split.

How are identical twins conceived?

The conception of identical twins occurs as usual, that is, during the process of fertilization, 1 male and 1 female germ cells merge with each other, resulting in the formation of a new cell - a zygote, which must subsequently divide and develop inside the woman.

Approximately 3-7 days after conception, this zygote for some reason bifurcates, and two separate cells attach and begin to develop in the uterus, which subsequently turn out to be two different same-sex fetuses with an identical genotype.

Identical twins with IVF

During the IVF procedure, conception occurs directly in a test tube and on approximately the 3rd day, the resulting embryos are implanted into the woman’s uterus, where they must subsequently grow and develop. In order to increase the chances of pregnancy, doctors always insert several fetuses into the uterine cavity, most often 2-3, in the hope that at least one of them will take root.

Sometimes it happens that both embryos take root, and at the time of implantation into the uterus, one of the zygotes divides into two more, and as a result, identical twins develop from this cell. When confirming the fact of pregnancy as a result of IVF, the woman is told about the number of implanted embryos and if there are more than two, then in order to increase the chances of pregnancy and birth, reduction (removal) of “extra” embryos from the uterus is carried out.

Diagnosis of identical twins: when are they visible on ultrasound?

In case of a successful pregnancy, the first screening is prescribed to a woman between 11 and 13 weeks. It is at this time that the doctor detects the presence of several fetuses in the uterus and can accurately determine the type of twins - monozygotic or dizygotic, whether the children have the same placenta or different ones, are located in a common amniotic sac or each has their own.

During IVF pregnancy, it happens that on an ultrasound at 5 weeks the doctor sees 2 embryos, which were planted in the woman’s uterus, and on the next ultrasound at 7-8 weeks 3 embryos are found in the uterus, this indicates that one of the zygotes has split , resulting in monozygotic twins.

Development of identical twins

The intrauterine development of monozygotic or identical twins largely depends on the presence of a common placenta and amniotic sac.

When babies are placed in separate amniotic sacs, but with one placenta, there is a risk of stealing one of the fetuses, as a result of which the “stronger” baby receives more nutrients and oxygen. Usually one of the babies (“weak”) is born weighing 500-600 g less than his brother or sister; in severe cases, the weak child of twins may lag somewhat behind in development from the stronger baby.

When fetuses are located in the same amniotic sac, there is a risk of babies getting entangled in each other's umbilical cords, which can lead to intrauterine asphyxia and death.

Irina Levchenko, obstetrician-gynecologist, especially for the site website

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 suggest at the everyday level, without delving into the exact definitions, to 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) during intrauterine development is 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 is between 4 and 8 days 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. in one of them the location or appearance of some objects of the body may be the same as if the other 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. In fact, these are two different children; 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 having 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.