A true “epidemic” of multiple gestations 1 , 2 has been recorded over the last two decades: the 2014 Practice Bulletin of the American College of Obstetricians and Gynecologists (ACOG) 3 reports that in the United States, the rate of twin births increased 76% between 1980 and 2009, from 18.9 to 33.3 per 1000 births (Figure 21.1). These impressive rises concerned not only simple twin pregnancies. Mainly as a consequence of the spread of assisted reproductive technology (ART) procedures, the rate of triplet and higher-order multifetal gestations rose more than 400% during the 1980s and 1990s, peaking at 193.5 per 100,000 births in 1998, followed by a modest decline to 153.4 per 100,000 births by 2009. 3 Temporal trends and changes in twinning rates in the United States, 1980–2009. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315382104/214c229b-14ed-4e52-a0d1-fb31003975c1/content/fig21_1.tif"/> (From Ananth, C.V. and Chauhan, S.P., Semin. Perinatol., 36, 156, 2012. With permission.)