Twin pregnancies with a 'vanished' embryo: a higher risk multiple gestation group?

BACKGROUND: Prior studies have documented increased risks to the offspring of IVF singletons that result from a vanished twin pregnancy. We aim to investigate the effect on perinatal outcomes of having an early vanished triplet in IVF twins. METHODS: This is a retrospective cohort study of twins from a large academic IVF practice. Multivariate analysis was performed to examine the perinatal risks-including small for gestational age (SGA), low-birthweight (LBW), preterm delivery and early preterm delivery-in twins that resulted from an early vanished triplet compared with twins without a vanished embryo. RESULTS: Of 829 IVF twin deliveries, 59 were a result of vanished triplet pregnancies (7.1%). There was no significant increase in SGA, LBW or delivery <37 weeks in the vanished triplets compared with other twins; however, the risk of early preterm birth (<32 weeks) was significantly higher (OR 3.09, 95% CI 1.63-5.87) and the length of gestation of these pregnancies was on average 1.5 weeks shorter (P < 0.01). In addition, the unadjusted mean birthweight was lower by nearly 200 g in the vanished triplet pregnancies (P < 0.01). CONCLUSIONS: IVF twin pregnancies with a vanished triplet are at an increased risk for early preterm birth compared with other twin pregnancies. These pregnancies should be recognized at higher risk for early preterm birth and considered for increased obstetrical monitoring. A significant limitation of this study is that the cause for preterm birth was unknown.