Objective: To compare perinatal and peripartum outcomes of vanishing twin gestations with singleton and dichorionic twin gestations in pregnancies conceived by in vitro fertilization.
Methods: We conducted a retrospective cohort study of vanishing twin pregnancies after fresh and cryopreserved autologous in vitro fertilization cycles performed at our institution from 2007 to 2015. Singleton, dichorionic twin, and dichorionic twin pregnancies with spontaneous reduction to one by 14 weeks of gestation (vanishing twins) were included. Analysis was restricted to patients with a live birth delivery at our institution at or beyond 24 weeks of gestation. The primary outcomes were gestational age and birth weight at delivery; secondary outcomes included peripartum morbidities. A subanalysis further differentiated the vanishing twin pregnancies between those in which demise of the twin occurred before compared with after identification of fetal cardiac activity. Logistic regression models were used to estimate the adjusted odds ratio (OR) with a 95% CI of outcomes.
Results: There were 1,189 pregnancies that met inclusion criteria (798 singleton, 291 twin, and 100 vanishing twin). The mean gestational age at birth and birth weights were 38.6±2.3 weeks of gestation and 3,207±644 g in singleton pregnancies, 35.5±2.7 weeks of gestation and 2,539±610 g in twin pregnancies, and 38.5±1.8 weeks of gestation and 3,175±599 g in vanishing twin pregnancies. When compared with twins, those with a vanishing twin had lower odds of preterm delivery (OR 0.13, 95% CI 0.07-0.23; adjusted OR 0.12, 95% CI 0.07-0.22) and small-for-gestational-age birth weight (OR 0.24, 95% CI 0.13-0.45; adjusted OR 0.14, 95% CI 0.07-0.28).
Conclusion: In pregnancies conceived by in vitro fertilization that progress to at least 24 weeks of gestation, vanishing twin and singleton pregnancies had similar perinatal and peripartum outcomes. Both were significantly better than twin pregnancies.