Vanishing twin after 12 gestational weeks is associated with adverse perinatal outcomes in in vitro fertilization cycles

Background: To assess the associations between vanishing gestational age and the adverse perinatal outcomes following in vitro fertilization cycles. Methods: This is a retrospective cohort study conducted in Guangzhou Women and children hospital from January 2011 to January 2019. We identified 350 vanishing twin pregnancies including 54 secondary fetal deaths and 296 singleton deliveries compared to 2080 infants from single gestations. The children detected by transvaginal ultrasonography in gestational week 6. By linking with the hospital's registries, the main endpoints were gestational age (weeks), birth weight (g), low birth weight (LBW), preterm birth and neonatal malformation rate. Perinatal outcomes were compared among study groups and controls. Results: Of the 350 vanishing twin, there were 15.4% (54) secondary fetal death. Of the 2376 singleton deliveries, 12.5% (296) originated from a twin gestation. In the assessment of perinatal outcome, there were no significant differences between the singleton cohort and vanishing twin before the presence of fetal cardiac activity cohort (VT before CA) and early vanishing cohort. The late vanishing twin group had a higher risk of preterm delivery (P < 0.001) and LBW (P 0.001). There were no significant differences between all cohorts in assessing neonatal malformation rate (P 0.05). Conclusion: Vanishing twin after 12 weeks is a predictor of adverse perinatal outcome. The couples with a viable fetus or a non-viable fetus and an empty gestational sac in early pregnancy (<12 weeks) have a similar outcome as the baby from a singleton delivery without vanishing.