Twin, Triplet, and Higher-Order Multifetal Pregnancies

Abstract

The incidence of multifetal gestations in the United States has increased dramatically over the past several decades. The rate of twin births increased 76% between 1980 and 2009, from 18.9 to 33.3 per 1,000 births (1). The rate of triplet and higher-order multifetal gestations increased more than 400% during the 1980s and 1990s, peaking at 193.5 per 100,000 births in 1998, followed by a modest decrease to 153.4 per 100,000 births by 2009 (2). The increased incidence in multifetal gestations has been attributed to two main factors: 1) a shift toward an older maternal age at conception, when multifetal gestations are more likely to occur naturally, and 2) an increased use of assisted repro- ductive ductive technology (ART), which is more likely to result in a multifetal gestation