Effects of fetal number and multifetal reduction on length of in vitro fertilization pregnancies

OBJECTIVE: To determine the effects of multifetal reduction and other variables on the duration of gestation of in vitro fertilization (IVF) pregnancies. METHODS: All 274 IVF pregnancies from the inception of the Women and Infants' Hospital IVF Program on May 26, 1988, until December 31, 1993, were evaluated. RESULTS: Spontaneous reduction occurred in ten pregnancies, and multifetal reduction was elected in 28 multiple gestations. Among 260 pregnancies that remained viable beyond 20 weeks, 162 singletons (37.9 +/- 0.29 weeks; mean +/- standard error) had a longer mean gestation than did 64 twins (34.6 +/- 0.61 weeks), 25 pregnancies reduced to twins (33.4 +/- 1.0 weeks), or nine triplets (29.7 +/- 1.9 weeks). Triplets delivered 4.9 weeks earlier than nonreduced twins (P < .05) and 3.7 weeks before twins resulting from multifetal pregnancy reduction (P < .05). Regression analysis showed that at the 8-week ultrasound, each viable fetus could be expected to reduce the duration of the gestation by about 3.6 weeks, and each fetus reduced medically or as a result of natural causes could be expected to prolong the gestation by approximately 3.0 weeks. Only 14% of triplet pregnancies underwent spontaneous multifetal reduction. CONCLUSION: Multifetal reduction of pregnancies with three or more fetuses was beneficial and increased the duration of gestation.