Early spontaneous multiple fetal pregnancy reduction is associated with adverse perinatal outcomes in in vitro fertilization cycles

The primary objective of this study is to investigate whether early spontaneous multiple fetal pregnancy reduction, also known as vanishing twin syndrome, is associated with adverse perinatal outcomes in fresh in vitro fertilization cycles. This is a retrospective cohort study of women with live singleton births with and without an early vanishing twin after fresh in vitro fertilization. Characteristics compared included incidence of preterm birth, overall birth weight, overall low birth weight, overall very low birth weight, and term low birth weight. In all, 4049 patients with live singleton births were included—853 and 3196 with and without a vanishing twin, respectively. The vanishing twin group had a lower overall birth weight compared to those without (3279.5 ± 369.9 vs 3368.6 ± 567.5 g; p < 0.01). Early vanishing twin was also associated with an increased odds of overall low birth weight (odds ratio: 1.75; 95% confidence interval: 1.36–2.25; p < 0.01) and increased odds of term low birth weight (odds ratio: 3.44; 95% confidence interval: 2.14–5.53; p < 0.01). Our study suggests that early vanishing twin is associated with lower overall birth weight and higher odds of overall low birth weight and term low birth weight in live singleton births after fresh in vitro fertilization.