Consequences of vanishing twins in IVF/ICSI pregnancies

BACKGROUND: Spontaneous reductions are a possible cause of the increased morbidity in IVF singletons. The aim of this study was to assess incidence rates of spontaneous reductions in IVF/ICSI twin pregnancies and to compare short- and long-term morbidity in survivors of a vanishing co-twin with singletons and born twins. METHODS: We identified 642 survivors of a vanishing co-twin, 5237 singletons from single gestations and 3678 twins from twin gesta-tions. All children originated from pregnancies detected by transvaginal sonography in gestational week 8. By cross-linkage with the national registries the main endpoints were prematurity, birth weight, neurological sequelae and mortality. RESULTS: Of all IVF singletons born, 10.4 % originated from a twin gestation in early pregnancy. Multi-ple logistic regression analyses adjusted for maternal age, parity and ICSI treatment showed for birth weight <2500 g an odds ratio (OR) of 1.7 [95 % confidence interval (CI) 1.2–2.2] and for birth weight <1500 g OR 2.1 (95 % CI 1.3–3.6) in singleton survivors of a vanishing twin versus singletons from single gestations; corresponding figures were seen for preterm birth. This increased risk was almost entirely due to reductions that occurred at>8 weeks gestation. We found no excess risk of neurological sequelae in survivors of a vanishing co-twin versus the singleton cohort; however, OR of cerebral palsy was 1.9 (95 % CI 0.7–5.2). Furthermore, we observed a correlation between onset of spontane-ous reduction, i.e. the later in pregnancy the higher the risk of neurological sequelae (r = –0.09; P = 0.02). Adjuste