Adverse obstetric outcome for the vanishing twin syndrome.

The aim was to compare obstetric outcomes of IVF singleton pregnancies diagnosed with vanishing twin (VT) syndrome with those pregnancies originating as singleton pregnancies and with twin pregnancies. In this case control study, 57 patients diagnosed with VT syndrome were matched and compared with 171 singleton controls and 171 twin controls. Mean gestational age was 35.1+/-3.7 versus 38.2+/-2.6 weeks (P=0.001) for patients and singleton controls respectively. Birth weights were 2834.4+/-821.2 versus 3036+/-489.3g (P=0.02), proportion of low birth weight (< 2500 g) was 33.3 versus 11.7% (P=0.0001) and very low birth weight (< 1500 g) 3.5 versus 0.6% for patients and singleton controls respectively. The proportion of deliveries before 28 weeks of gestation was 7.0 versus 1.2% (P=0.01) for patients and singleton controls respectively. When comparing the study group to twin control pregnancies, a similar gestational age at delivery (35 weeks) and rate of preterm birth (23%) were found. In conclusion, pregnancies diagnosed with the VT syndrome after IVF carry a higher rate of adverse obstetric outcomes in terms of preterm deliveries and lower birth weight, compared with IVF pregnancies that were originally singleton. Additionally, significant similarities were observed in the obstetrics outcome of vanishing twin pregnancies and twin pregnancies.