Does a Vanishing Twin Affect Perinatal Outcome?

Background: The impact of vanishing twin (VT) syndrome on obstetric outcome is currently unknown. The aim of this study was to compare obstetric and neonatal outcomes of VT with singleton and twin deliveries after assisted reproduction and to evaluate the impact of VT on pregnancy outcome. Methods: We analyzed 130 births at our hospital between January 2000 and February 2012 that resulted from assisted reproduction. Among these, 96 were singleton, 10 were VT, and 24 were twin deliveries. Vanishing twin was defined as a first-trimester (≤ 12 gestational weeks) embryonic loss of one of the twins. We compared the obstetric and neonatal outcomes of VT with singletons and twins, respectively. Results: The obstetric and neonatal outcomes were similar between VT and singleton deliveries, although there was a trend towards an increased rate of preterm delivery (9.4% vs. 20%, p=0.28), extremely preterm delivery (5.2% vs. 20%, p=0.13), and low birth weight <2500 g (30% vs. 73.3, p=0.023) in the VT group. Outcomes were significantly better in the VT group than in the twin group. The rate of preterm delivery was significantly higher in the twin group than in the VT group (20% vs. 70.8%). Furthermore, birth weight was significantly lower in the twin group than in the VT group (2798 ± 187 vs. 2046 ± 97), and the rate of low birth weight was higher in the twin group than in the VT group (30% vs. 73.3%). Conclusion: Obstetric and neonatal outcome after assisted reproduction may deteriorate according to pregnancy status in the following order: singleton, VT and twin pregnancy.