Impact of monozygotic twinning on multiple births resulting from in vitro fertilization in the United States, 2006–2010

Objective To determine the contribution of monozygotic twining to in vitro fertilization multiple births. Study Design We performed a retrospective analysis of the incidence of monozygotic twining in multiple births resulting from fresh embryo transfers using 2006-2010 data from the Society for Reproductive Technology Clinic Outcome Reporting System. Results The number of embryos transferred were fewer than the number of births in 0.5% (223/40950) of twin, 29% (659/2289) of triplet, and 64% (43/67) of quadruplet births resulting from transfer of fresh embryos from 2006 to 2010. In 2010, 37% of triplets and 100% of quadruplet births occurred when fewer than 3 and fewer than 4 embryos respectively were transferred. Conclusion Monozygotic twinning plays a key role in the development of triplet and quadruplet pregnancies achieved through in vitro fertilization.