Multiple pregnancy is the bearing of two or more fetuses by a pregnant woman. It differs from a singleton by a faster increase in the volume of the abdomen (starting from the 2nd trimester of gestation), accelerated weight gain, high standing of the uterine fundus, intense stirring in different parts of the uterus, probing of many small parts, 3 and larger parts, the appearance of specific external signs (furrows between twins on the front wall of the abdomen, saddle uterus). It is diagnosed by ultrasound, determination of levels of AFP, HCG. When accompanied, it requires more careful supervision. More often it ends with operative delivery.
ICD 10
O30 Multiple pregnancy
General information
The frequency of multiple pregnancies in different regions ranges from 1 to 2%, while the prevalence of monozygotic twins remains relatively stable (0.35-0.5%), and dizygotic tends to increase, which is associated with more frequent use of reproductive technologies (IVF, induction of conception). Over the past 20 years, multiple gestations in developed countries have been registered twice as often (1:50 versus 1:101 at the end of the last century). The birth rate of twins is 1 in 87 births, triplets — 1 in 6,400, four fetuses or more — 1 in 51,000. The probability of multiple conception increases with the age of a woman and depends on race (multiple births are more common in African peoples and very rarely in Asians).
Causes of multiple pregnancy
The development of two or more fetuses in the uterus is the result of fertilization of several eggs or division of the embryo in the early stages of development (usually at the stages of zygote, morula, blastula). The causes of multiple identical pregnancies have not yet been sufficiently studied. Multiple gestations, according to the observations of specialists in the field of obstetrics, are associated with the influence of the following factors:
- Application of modern reproductive technologies. In 30%, multiple pregnancy is the result of in vitro fertilization with embryo transfer, in 20-40% — the appointment of human menopausal gonadotropin, in 5-13% — the use of other ovulation stimulants. Drug stimulation of ovarian tissue often causes more than one egg to mature and exit from the ovary. IVF was initially based on the idea of superovulation with fertilization of several mature eggs and planting 2-6 fetal eggs in the uterus.
- Multiple spontaneous ovulation. Up to 1% of multiple gestations are associated with the maturation of several eggs in the ovary. Spontaneous ovulation often occurs after the withdrawal of COCs: if conception occurs within a month after the completion of hormonal contraception, the probability of developing multiple pregnancy increases by 2 times. The release of several mature eggs is possible in patients older than 35 years, women with elevated levels of pituitary gonadotropins. Conception of a second child in the same ovulatory cycle is called superfecundation.
- Hereditary predisposition. Twins are more often born to representatives of the Negroid race, in women who have endured multiple pregnancies, they themselves belong to twins or have such relatives. In the course of genetic studies, DNA sites responsible for the development of multiple pregnancy have been identified. Since in most cases they are associated with the X chromosome, the tendency to multiple conception is usually inherited through the female line, although a male carrier of the gene can also pass it on to his daughters.
In some patients, ovulation persists after pregnancy, so with unprotected sex, superfetation is possible — fertilization of the egg from the next ovulatory cycle. The likelihood of multiple dizygotic gestation increases in patients with abnormalities of the development of reproductive organs (bicornular or saddle-shaped uterus, the presence of an intrauterine septum). In such cases, it is easier for two fertilized eggs to be implanted into the endometrium without competing with each other. The risk of multiple conception is increased by 10-20 times in women who received chemotherapy and radiation therapy for lymphogranulomatosis, which is probably associated with superovulation during the restoration of menstrual function.
Pathogenesis
The mechanism of development of multiple pregnancy depends on its variant. When carrying fraternal twins, each of the zygotes develops independently and is implanted separately into the uterine wall, forming its own placenta and fetal membranes. If multiple gestation is identical, the time of division of the fertilized egg plays an important role in its development. When the zygote is split within 0-72 hours after conception, placentation is the same as in fraternal twins — bichorial-biamnial. This variant of multiple monozygotic pregnancy is observed in a quarter of cases.
In 70% of pregnant women, embryo division occurs on the 4th-8th day of gestation after nidation and chorion formation, as a result, each of the fetuses has its own shells, but develops on a common chorial site. In 5% of monozygotic pregnancies, the embryo divides after the formation of chorion and amnion (on the 9th-13th day). As a result, the fruits grow in a common shell and receive nutrition from a single placenta. Splitting of the embryo after the 13th day of development is usually incomplete (conjoined or Siamese twins). In rare cases, mono- and dizygotic twins develop simultaneously in the uterus.
Classification
The systematization of the forms of multiple pregnancy is carried out taking into account the criteria of zygosity and the type of placentation. This approach makes it possible to fully assess possible risk factors and develop optimal pregnancy management tactics. Depending on the number of fertilized eggs from which twins began to develop, obstetricians and gynecologists distinguish:
- Dizygotic pregnancies. They are observed in 2/3 of cases of carrying twins. They arise as a result of fertilization of different eggs by different spermatozoa. Each of the twins has its own genetic material and develops independently. Dizygotic twins can be both same-sex and heterosexual. Subsequently, the children have noticeable differences in appearance.
- Identical (monozygotic) pregnancies. They develop in 1/3 of cases of multiple gestations due to early separation of an oocyte fertilized by a single sperm. The genetic material of twins is identical, so they are always same-sex, have the same blood type and look similar to each other. The structure of the fetal membranes depends on the time of splitting of the embryo.
According to the type of choriality, there are bichorial-biamnial and monochorial placentation, observed in 80% and 20% of multiple gestations, respectively. Two placentas can be separated (if there is a distance between the implanted embryos) and merged (when forming a common decidual shell in embryos implanted nearby). All dizygotic pregnancies are bichoric-biamnial. In monochorionic gestations, the fetuses have a single placenta. Such multiple births can be monochorially-biamnial (with separate fetal membranes of each embryo) and monochorially-monoamnial (with a common amnion).
Symptoms of multiple pregnancy
In the first trimester of the gestational period, pathognomonic signs indicating the presence of several fetuses in the uterus are usually not determined. Starting from the middle of the second trimester, a woman often notes a rapid (abrupt) increase in abdominal volume and a significant weight gain exceeding the gestational norm. At later stages, the movements can be felt simultaneously in different parts of the uterus, 3 or more large fetal parts (heads, pelvic ends) are palpated, handles and legs are well felt in various places of the abdomen. In the third trimester, a longitudinal, oblique or transverse furrow between the fruits may appear on the abdominal wall. Sometimes the shape of the growing uterus becomes saddle-shaped with protruding corners and a deepened bottom.
Complications
Due to the frequent complicated course, multiple pregnancies are classified as pathological. Most often, it is complicated in first-time mothers with induced conception: in the 1st trimester, disorders are detected in 94% of pregnant women, in the 2nd — in 69%, in the 3rd – in almost all observed women. With twin gestations, early toxicosis is more pronounced, anemia occurs earlier and increases faster due to accelerated consumption of iron reserves, gestosis is more often diagnosed, including preeclampsia and eclampsia, gestational diabetes and hypertension, cholestasis of pregnant women, pyelonephritis, constipation, varicose veins.
Twinning is a significant risk factor for premature termination of gestation. The risk of spontaneous miscarriages with multiple pregnancies doubles. Due to the overgrowth of the uterine wall and the occurrence of cervical insufficiency in 37-50% of patients, contractions begin earlier: when carrying twins, childbirth usually takes place at 35-36 weeks, triplets — on the 33rd, fours – on the 29th. In 25% of cases, the membranes are prematurely ruptured and amniotic fluid is poured out, after which the umbilical cord and small fetal parts may fall out. More often, the placenta peels off prematurely, the contractile activity of the myometrium is disrupted, the soft tissues of the birth canal are injured. 20% of maternity patients have bleeding. After childbirth, subinvolution of the uterus is possible.
5-8% of multiple gestations are complicated by hydroamnion (polyhydramnios), the risk of shell attachment and presentation of the umbilical cord increases 7-8 times, umbilical cord entanglement is detected in 25% of fetuses. Intrauterine developmental delay is determined in 70% of twins. Due to the more frequent development of fetoplacental insufficiency and premature onset of labor, over 55% of children are born with a weight of up to 2500 g, the indicators of perinatal morbidity and mortality are tripling. In 5.5% of pregnancies, the fruits are arranged longitudinally and transversely, in 0.5% — transversely. The rapid postpartum contraction of the uterus contributes to the transition of the remaining twin from the longitudinal position to the transverse one.
In newborns, congenital defects are more often detected (splices between themselves, consequences of acardia syndrome, hydrocephalus, cardiac defects, asymmetric skull, deformed feet, hip dislocation, etc.), respiratory distress syndrome, necrotic enterocolitis, septic disorders, intracranial hematomas occur, the incidence of cerebral palsy increases 6-7 times. The specific consequences of multiple gestations are considered to be fetal-fetal transfusion syndrome, reduction of one of the twins, interlacing of the umbilical cords with a common amnion, coupling (collision) in childbirth.
Diagnostics
The use of modern screening methods of research when registering a patient in a women’s clinic makes it possible to diagnose multiple pregnancies in time, even at early gestational stages. The most informative methods that allow us to assume and confirm the bearing of more than one child by a woman are:
- Ultrasound. Echographic examination is the gold standard for the diagnosis of multiple pregnancy. With the help of ultrasound in the early stages, it is possible to identify several fetuses, to determine the features of placentation. Subsequent ultrasound screening in the 1st, 2nd, and 3rd trimesters provides adequate control over the course of gestation and allows timely detection of possible complications.
- Determination of HCG and AFP levels. Chorionic gonadotropin and alpha-fetoprotein are specific gestational markers. Since AFP is produced by the liver and gastrointestinal tract of a developing child, and HCG is produced by the fetal membranes, in pregnant women carrying twins, the concentration of these hormones in the blood increases by 4 times or more compared to single pregnancies.
Clinical examination of blood and urine for the diagnosis of possible complications, fetometry and phonocardiography, providing control of the development of twins, cervicometry, which allows timely detection of isthmic-cervical insufficiency, are recommended as additional examination methods. Although in 99.3% of cases, multiple pregnancy is determined by ultrasound, in some cases, differential diagnosis with hydroamnion, large fetus, uterine fibroids, cystic drift may be required. If there are indications, the patient is consulted by an oncogynecologist, a neonatologist.
Management of multiple pregnancies
Taking into account the high probability of a complicated course, patients with multiple pregnancies are recommended to observe a gentle regime (restriction of physical and psycho-emotional loads, sufficient sleep and daytime rest), a special diet to meet the increased need for proteins, carbohydrates, fats, vitamins and trace elements, dynamic monitoring to assess the condition of women and children. Special attention is paid to the prevention of anemia, early diagnosis of cardiovascular and renal pathology, hemostasis disorders. If gestosis and other complications are detected, hospitalization in an obstetric hospital is preferable. A pregnant woman with uncomplicated multiple gestation is sent to the maternity hospital 2-3 weeks before the expected delivery, when carrying three fetuses or more — for 4 weeks, with monochorial placentation — at 26-27 weeks. When choosing the method of delivery, the presence of complications, the number of twins, their size and position in the uterus are taken into account. To end pregnancy , it may be recommended:
- Natural childbirth. Although multiple pregnancy does not serve as a direct indication for cesarean section, delivery through the birth canal is used less often in twin pregnancies than in single pregnancies. Natural childbirth is possible in the presence of twins, when the twins are in the longitudinal position and head presentation. With normal indicators of fetal development, it is recommended to induce labor activity at 37 weeks.
- Operative delivery. Cesarean section is performed as planned when carrying large or Siamese twins, more than two fetuses, unavailability of the birth canal after 37 weeks of gestation, pelvic presentation of the first twin, transverse position of the first or both fetuses, hypoxia. Emergency surgical intervention is performed in case of a sudden threat to the mother or fetus (placental abruption, etc.).
According to indications, during pregnancy, patients may undergo surgery to eliminate or correct fetal transfusion syndrome (amnioreduction, endoscopic laser coagulation of anastomosed placental vessels, septostomy, in exceptional cases — selective euthanasia of the donor fetus). In case of natural delivery after the appearance of the first twin, it is sometimes allowed to perform an external rotation on the head of the remaining child under ultrasound control. In multiple births, measures are needed to prevent postpartum blood loss.
Prognosis and prevention
The risk of complications and the outcome of a multiple pregnancy are determined by its choriality. Although the prognosis is in any case less favorable than with singleton gestations, the greatest number of complications and perinatal losses occur with monochorionic multiple pregnancy. Effective measures for the prevention of multiple conception have not been proposed to date. To prevent possible complications, early registration and regular observation by an obstetrician-gynecologist, balanced nutrition, fortification, more frequent rest in the side position are recommended.