Twins and twins

Multiple pregnancy is called, in which two fetuses or more develop simultaneously. If a woman is pregnant with two fruits, they talk about twins, three fruits - about a triple, etc. Children born from a multiple pregnancy are called twins.

Multiple pregnancy occurs in 0.7-1.5% of cases. At present, there is a tendency to increase its frequency in connection with ovulation hyperstimulation in women with infertility when using assisted reproductive technologies. At the same time, several follicles (3-4 or more) are maturing at the same time, and, consequently, several pregnancies may result from fertilization of several oocytes.

The frequency of multiple pregnancies can be determined by the Haase formula (1895). According to this formula, the genus of twins occurs once for 80 genera, triplets - once for 802 (6400) genera, the fourth - once for 803 (51200) births.

With multiple pregnancies and childbirth, complications occur more often than with singleton fetuses. Perinatal mortality in multiple pregnancies is 3-4 times higher than in single-fetal pregnancy. Perinatal losses are directly related to the body weight of children, averaging 10%. Perinatal mortality among monozygotic twins is 2.5 times higher than among dizygotic twins, and is especially high in monoamnotic twins.

Identical twins

There is no single-valued hypothesis for the formation of identical twins. Obviously, most often the appearance of identical twins (troines, etc.) is associated with the fertilization of an egg that has two or more nuclei. Each nucleus combines with the nuclear substance of the sperm and forms a fetus. Eggs with two and three nuclei were identified. There is also another mechanism for the origin of identical twins: a single embryonic rudiment in the fragmentation stage is divided into two parts, a fetus is formed from each part.

When dividing to the formation of the inner layer (in the stage of the morula) and the transformation of the outer layer of the blastocyst ducts into the chorionic elements, which occurs in the first 72 hours after fertilization, two amniotic sacs and two choriones develop. As a result, bi-amniotic biochoric monozygotic twins are formed.

If the separation takes place on the 4th-8th day after fertilization, after the formation of the inner layer of the fibers and the filling of the chorion from the outer layer, but before the amniotic cells are laid, that is, before the appearance of the fetal bladder, two embryos are formed, each in a separate amniotic sac monohorial biamnotic monozygotic twins. Most monozygotic twins (70-80%) are represented by this type.

If, by the time of separation, the amniotic tab has already occurred, which occurs on the 9th-12th day after fertilization, the division leads to the formation of two embryos in one amniotic sac, that is, a monohorial monoamniosic monozygotic twins. This is the most rare type of monozygotic twins, which occurs in approximately 1% of cases of monozygotic twins. However, there is a significant risk in terms of pregnancy.

After the 15th day, complete separation of embryonic rudiments is impossible. In this case, fused twins develop. This type is rare enough, approximately 1 in 1500 many fetal pregnancies.

Odnoyaytsovye twins are always same-sex, have the same blood group, the same color of eyes, hair, skin relief of fingertips, the shape and location of teeth and are very similar to each other. They, as a rule, suffer from the same diseases at the same time, have the same learning abilities.

With monochorion biamniotic monozygotic double, the membrane that separates the two amniotic cavities is fairly transparent, it does not have vessels, as well as residues of the decidual membrane and trophoblast. In this case, a certain type of connection of the fetoplacental blood circulation systems of twins is always observed to varying degrees, which contributes to the development of transfusion syndrome.

It should be noted that in monochorionic placentas vascular anastomosis can be detected quite often - arterioarterial or arteriovenous, which causes the development of fetofetal transfusion syndrome. The arteriovenous connection is through the capillary system of the placenta. Because of this anastomosis, blood flows from the artery to the vein from one fetus to another. In the bichoric placentas, the arteriovenous anastomosis develops much less frequently. The consequences of such an anastomosis can be very serious. If in the vascular system of the placenta the blood pressure is symmetrical, both twins are 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 (a recipient) than the other (donor), the latter does not receive sufficient nutrition and is in worse conditions for its development, which can cause delay fetal development, with a sharp imbalance in the placental blood circulation system, one of the twins (the donor) is gradually depleted, dies and mummified, turning into a "paper fruit" (fetus pa pyraceus). Often a twin-recipient develops hydration and dropsy caused by heart failure.

Twins Twins

Of all the species of twins, the doublets are observed in 70% of cases.

The formation of double-sided twins is possible in the case of:

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

About such variants of the origin of twins are evidence of two operative interventions of two or more yellow bodies of the same age in one or both ovaries.

Dizygotic twins are always characterized by a bihorial, biamnotic type of placentation. In this case there will always be two autonomous placentas that can fit tightly, but they can be divided. Each fertilized egg that penetrates the decidual membrane forms its own amniotic and chorial membranes, from which the placenta subsequently forms. If the eggs penetrated into the decidual membrane closely to one another, then the edges of both placenta closely adhere, which creates the impression of a unified formation. In reality, each placenta has its own vascular network, each fetal sac has its own amniotic and chorial membranes. The septum between two fetal sacs consists of four membranes: two amniotic and two chorionic, and the decidual envelope is common (bichorial twins). If the fertilized eggs penetrate a considerable distance, the placentas develop as separate formations, and each fetal egg has its own, separate decidual envelope.

Twins twins can be either mono- or heterozygous and have the same genetic dependency as their own siblings.

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