Consequences of Vanishing Twins in IVF/ICSI Pregnancies

Abstract

In Denmark, 4% of children at present are born by in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Singleton IVF/ICSI infants are relatively likely to be preterm and have low birth weight. Spontaneous reductions may increase morbidity in singleton IVF infants. Previous work indicates that “vanishing” twins is not the only factor in adverse outcomes. The authors analyzed data on women with ongoing IVF/ICSI pregnancies that were detected by transvaginal sonography in gestational week 8. The goals were to determine the frequency of spontaneous reductions in IVF/ICSI twin pregnancies and to compare morbidity in survivors of a vanishing cotwin with both singletons and born twins. Included were 642 survivors of a vanishing cotwin, 5237 singletons from single gestations, and 3678 twins from twin gestations. Approximately 10% of all IVF singletons born resulted from a twin gestation in early pregnancy. On multiple logistic regression analysis, adjusting for maternal age, parity, and ICSI, the odds ratio (OR) for birth weight below 2500 g in singleton survivors of a vanishing twin was 11.7 (95% confidence interval [CI], 1.2–2.2), and for birth weight below 1500 g, it was 2.1 (95% CI, 1.3–3.6), compared with singletons resulting from single gestations. Corresponding figures were obtained for preterm births. The increased risk was almost entirely the result of reductions occurring after 8 weeks gestation. No increase in the risk of neurologic sequelae was found in survivors of a vanishing cotwin compared with singletons. The OR for cerebral palsy, however, was 1.9 (95% CI, 0.7–5.2). The later in pregnancy that spontaneous reduction began, the higher the risk of neurologic sequelae. The adjusted OR of child death was 3.6 (95% CI, 1.7–7.6) in survivors compared with the singleton cohort. These findings suggest that outcomes for IVF/ICSI survivors of a vanishing cotwin have poorer outcomes than singletons from single gestations. Because approximately 10% of IVF/ICSI singletons result from a vanishing twin pregnancy, this may explain the relatively adverse outcomes observed in IVF/ICSI singleton infants. These considerations favor elective single embryo transfer, which will reduce the high risk of twins and may also lessen the risk of spontaneous reduction and the poor outcomes associated with it.