"Vanishing" twins - Important new findings announced at ESHRE conference July 6th 2011

Epidemiological studies on vanishing twins and consequences for the surviving singletons

A. Pinborg Rigshospitalet, University of Copenhagen, The Fertility Clinic 4U71, Copenhagen, Denmark

Introduction: Recently, it has become evident that IVF singletons do worse than their naturally conceived counterparts. A possible cause is an increased number of spontaneous reductions (vanishing twin) as a consequence of the dual embryo transfer policy. We investigated incidence rates of spontaneous reductions in IVF/ICSI pregnancies and compared short- and long-term outcome including obstetric data, malformations, neonatal intensive care unit admissions, neurological sequelae and mortality in singleton survivors of a vanishing co-twin with IVF/ICSI singletons and twins from pregnancies without spontaneous reduction.

Materials and methods: A total of 9557 IVF/ICSI children were eligible; 642 survivors of a vanishing co-twin, 5237 singleton from single gestations and 3678 twins from twin gestations originating from clinical pregnancies detected by transvaginal sonography in gestational week eight. Data on obstetric outcome and neurological sequelae were obtained by cross-linkage with the national registnes. 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. Multiple logistic regression analyses adjusted for maternal age, panty and ICSI treatment showed: for birth weight <2500g an OR 1.7 (95% CI 1.2-2.2) and forbirth weight <1500g OR was 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. 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). Further we found a correlation between the time of onset of spontaneous reduction i.e. the later in pregnancy, the higher the risk of neurological sequelae (r= - 0.09, P=0.02). The risk of child death within the follow-up period was OR 3.4 (95% CI 1.6 7.2) in the survivor versus the singleton cohort.

Conclusions: One in ten IVF singletons origins from a twin gestation. This is one of the major causes for the higher risk of adverse obstetric outcome in IVF singletons. 

In other words, the loss of a twin before birth does have a physical consequence for the sole survivor. The psychological consequences however, are a matter for another conference, another time - our conference in fact!    [Download 2011 Womb Twin conference brochure]