3.1. Definition. Etiology. Classification
Definition. Pregnancy, in which two, three and more fetuses develop in the uterus, is called multiple. Multiple labor is the delivery of two or more babies.
Pregnancy with two fetuses is called twin pregnancy, three - triplets, etc. Babies born from multiple pregnancies are called twins. The incidence of multiple pregnancies is 1.5-3%. The growing incidence of multiple pregnancies in recent years is due to the introduction of new reproductive technologies in the treatment of infertility, in which methods of stimulation of ovulation (hyperstimulation) are used, as well as transfer of 2-3 embryos into the uterus with the use of in vitro fertilization (IVF) method. Triplets are born in 1-1.5% of multiple deliveries. In ovulation induction with gonadotropin, the incidence of multiple pregnancies increases by 16-40%, in superovula-
tion - by 25-30%.
Incidence of complicated pregnancy (miscarriage, preterm labor, pre-eclampsia, etc.), as well as perinatal mortality in multiple pregnancy is 3-4 times higher than in singleton pregnancy.
Perinatal mortality in multiple gestation is on average 5-fold higher than in singleton pregnancies. The highest mortality is observed in monozygotic twins and dissociated fetal growth retardation. However, prematurity is the main cause of high perinatal mortality in multiple gestation. Mortality of twins makes up 25% of the perinatal mortality in preterm newborns, and 10% of all cases of perinatal mortality. In addition to prematurity, the causes of perinatal mortality include fetal malformations, feto-fetal transfusion syndrome, pla-cental insufficiency, birth trauma, hypoxia of one or both fetuses.
Perinatal mortality (on average 10-12%) primarily depends on the body weight of the babies and the gestational age at which preterm delivery occurred.