Epidemiology and biology of multiple gestations.

Twins have always aroused interest and have been represented throughout history. Conjoined twins have caused even more sensation, the best-known pair being Chang and Eng Bunker, who were born in Thailand in 1811 and inspired the term Siamese twins. Recently, higher-order multiples have caused controversy, and there has been heavy media coverage of large-number deliveries, such as the McCaughey septuplets. In this article, we review the incidence, types, and causes of multiple gestations.