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Multiple gestation occurs in about 1.5% of all births. Multiple pregnancies of greater than three constitute a relatively small component of the total; however, these numbers are increasing as a result of the widespread use of assisted reproductive technologies.
Twins may result either from the splitting of a single fertilized ovum into two genetically identical individuals (monozygotic) or when two separate ova are each fertilized by a sperm, leading to genetically distinct siblings (dizygotic). Although the incidence of monozygotic twinning is fairly constant throughout the world at a rate of approximately 1 per 250 births, there is evidence that the use of ovulation induction drugs may almost double this figure. The frequency of dizygotic twinning is increased with African-American race, increasing maternal age up to 40 years, increasing parity, family history of twins, and, especially, use of assisted reproductive techniques.
Multiple gestation should be suspected when there is a history of use of a fertility agent, a discrepancy between the estimated gestational age and uterine size, or abnormally elevated laboratory screening tests such as maternal serum alpha-fetoprotein or triple screens.
Perinatal morbidity and mortality increase in direct proportion to fetal number. Complications related to preterm birth, such as respiratory distress syndrome, intracerebral hemorrhage, sepsis, and necrotizing enterocolitis, account for most of these adverse outcomes. Congenital malformations, fetal growth restriction, and umbilical cord prolapse also occur more frequently in multifetal pregnancies.
The shunting of blood from one placental circulation to the other through placental vascular anastomoses can lead to the twin-twin transfusion syndrome. This can cause marked discrepancies in fetal size and circulating blood volume, massive differences in amniotic fluid volume, and altered hemodynamics in either or both circulations that results in hypoxia or death in utero. The use of serial amniocentesis and newer techniques such as laser ablation of the communicating vessels has considerably improved the outcome for fetuses with this syndrome. Monozygotic twins also have a 1-2% incidence of monoamniotic sacs, which can be associated with sudden death in utero due to cord entanglement. In triplet pregnancies, perinatal mortality is increased 3-fold, infant mortality is increased 19-fold, and severe neurologic handicap.
Multiple gestations increase the maternal risk of hyperemesis triplets, quadruplets, sextuplets selective reduction.
Antenatal management should include attention to nutrition, avoidance of strenuous physical activity, frequent prenatal visits, and counseling on symptoms of preterm labor, PROM, and hypertensive disorders of pregnancy. Ultrasound assessment of fetal growth and amniotic fluid volume should be performed.
Embryo Reduction
The higher-order multiple gestations resulting from assisted reproductive technologies has resulted in an increased risk of preterm delivery, which is directly proportional to the number of fetuses developing in utero. Multifetal pregnancy reduction is a procedure designed to increase the chances of delivering closer to term.
Multifetal pregnancy reduction is usually performed via the transabdominal or transvaginal route. A needle is guided under direct ultrasonic visualization into the fetal heart or thorax, and potassium chloride solution.