Multiple pregnancy is called such a pregnancy, in which two or more fetuses develop simultaneously in the mother's body, the genera in this case are called multiply.
The frequency of birth of twins varies from 0.4 to 1.6%. The frequency of pregnancy twins is 1:80 triplets - 1: 802 quadruplets - 1: 803. Among the twins that are born, boys predominate.
The reasons for the occurrence of multiple pregnancies are not fully understood. Certain value in this has heredity. Often the cause of the occurrence of multiple birth is the use of drugs to stimulate ovulation, in vitro fertilization, stopping the use of oral contraceptives. Important are the anomalies of the development of the uterus (bicornic uterus or septum in the uterus), in which there is a simultaneous maturation in the ovaries of two or more oocytes. Multiple fetuses promote the fertilization of "old" eggs (a day or more after ovulation), the age of a woman after 35 years, exposure to harmful substances, lack of oxygen, cold, ultraviolet irradiation.
Multiple pregnancy can occur as a result of fertilization of two or more ovules, simultaneously matured (polyovulation), as well as the development of several embryos from one egg (polyembryonia).
The origin of the bivalent or bug-ower twins may be due to:
a) simultaneous ovulation with the subsequent fertilization of two or more ovules that matured in different follicles of the same ovary (ovulatio uniovularis)
b) simultaneous ovulation of two or more ovules that matured in the follicles of both ovaries (ovulatio biovarialis)
c) ovulation of several oocytes, simultaneously matured in one follicle (ovulatio unifollicularis).
Among twins, twins are more common, with bivalent twins: they are 2 times more than single-egg ones. In the case of binary twin fertilization, the ovum has an independent development, a separate aqueous and chorionic membrane, an independent network of vessels. When examining the afterbirth, two placentas manifest themselves. The membrane between the fruits with bizygotic twins consists of the amnion - the chorion - the chorion - the amnion: the bihorial biamnotic type of placentation. Binary twins can have different gender and different or identical blood group.
Pregnancy with monozygotic monozygotic twins comes as a result of the fertilization of several spermatozoa of a multinucleated egg or the distribution of hereditary material at the stage of crushing into two parts, with each forming a fetus. The monogamous twins have a common placenta, a decidual membrane, common vessels and two or one amnion: monochorion biamnotic type of placentation. With the development of pregnancy, monozygotic twins are more likely to develop fetal anomalies, umbilical attachment of the umbilical cord, the umbilical cord, may be a transfusion syndrome of twins (blood moves from the arteries to the veins, from one fetus to another), which leads to a delay in the fetal development of one fetus, vascular insufficiency, anemia, and polyhydramnios.
The identical twins are always of the same sex, are very similar to each other. The blood group and Rh factor are the same. When examining the litter, one placenta is determined, the membrane between the amniotic cavity consists of only two amnions, and the decidual envelope is the only one.