Natural History of Multiples Conceived by In Vitro Fertilization

Figure 22.1 shows the distribution of clinical pregnancies according to plurality in the years from February 1987 to 2003. Altogether, there were 787 clinical pregnancies including 316 (40.2%) multiples, of which 112 sets (14.2%) were high-order multiples1. In comparison, data from the UK show 25% twin and 5% triplet pregnancies2, whereas US data show 32% twin and 6% triplet pregnancies3, differing primarily from the Reggio Emilia data by the high-order multiples rate.