Chapter 214 Multiple Gestation
INTRODUCTION
Prevalence: Occurs in 3.4% of births in the United States (and increasing; 70% since 1980); 1/10,000 births for spontaneously occurring triplets. (The increase in multiple births is thought to be due to the use of fertility drugs and an increased rate of childbearing in women older than age 30, who are more likely to conceive multiples.) Multiple gestations are responsible for a disproportionate share of perinatal morbidity and mortality. (They account for 17% of all preterm births [before 37 weeks of gestation], 23% of early preterm births [before 32 weeks of gestation], 24% of low-birthweight infants [<2500 g], and 26% of very-low-birthweight infants [<1500 g].) Hospital costs for women with multiple gestations are on average 40% higher than for women with gestational-age–matched singleton pregnancies because of their longer length of stay and increased rate of obstetric complications.
ETIOLOGY AND PATHOGENESIS
Causes: Monozygotic twins result from the cleavage of a single fertilized ova (4/1000 births). Dizygotic multiple gestations occur when there are multiple ova released and fertilized (naturally or through assisted ovulation. See later.).
DIAGNOSTIC APPROACH
Differential Diagnosis
Associated Conditions: Prematurity, cord accidents, intrauterine growth restriction (50% to 60% of triplet or greater pregnancies), polyhydramnios, increased fetal morbidity and mortality, increased risk of congenital anomalies, abruptio placenta, placenta previa, hypertension and pre-eclampsia, anemia, acute fatty liver, gestational diabetes, hyperemesis gravidarum, pyelonephritis, cholestasis, thrombosis and embolism, postpartum hemorrhage, increased operative delivery rate.
Workup and Evaluation
Laboratory: No special evaluation indicated, although because of the higher incidence of gestational diabetes, screening is of greater importance. (Abnormality of gestation-sensitive laboratory tests, such as maternal serum alpha-fetoprotein [MSAFP], is to be expected.)
Imaging: Ultrasonography (reduces the rate of undiagnosed multiple gestation from 40% to <5%). Radiographic studies are generally inadequate to establish the presence or health of a multiple pregnancy, making routine use of x-rays undesirable.
Special Tests: Genetic amniocentesis may be considered (twin pregnancies have twice the rate of abnormalities: monozygotic = 2% to 10% rate).
