Multiple births are increasing in the United States and contribute disproportionately to perinatal and neonatal mortality and morbidity. (See "Perinatal mortality", section on 'Multifetal pregnancies'.)
The incidence, mechanisms, complications, and pediatric management of multiple births are reviewed here. The antepartum and intrapartum management of twins and monoamniotic twin pregnancy are discussed separately. (See "Twin pregnancy: Prenatal issues" and "Twin pregnancy: Labor and delivery" and "Monoamniotic twin pregnancy".)
Twins and triplets naturally occur in approximately 1 in 80 and 1 in 8000 pregnancies, respectively, in the United States [1,2]. The incidence of spontaneous twins varies by country. The incidence of twins is lower in Japan and higher in Nigeria. (See 'Zygosity' below.)
Multiple pregnancies comprise an increasing proportion of the total pregnancies in the developed world due to older maternal age at childbirth and the expanded use of fertility treatments [3,4]. In countries with high rates of multiple births, 30 to 50 percent of twin pregnancies and 75 percent of triplet pregnancies occur after infertility treatment .
From the 1980 to 2008, the number of twin pregnancies has doubled in the United States with a birth rate of 32.6 per 1000 births in 2008 . The peak incidence of triplet, quadruplets, or higher order pregnancies occurred in 1998 at a rate of 193.5 per 100,000 live births, and has decreased to a rate of 147.6 per 100,000 births in 2008 .