Vanishing twins: a predictor of small-for-gestational age in IVF singletons

Pinborg, Anja
Lidegaard, Øjvind
Freiesleben, Nina la Cour
Andersen, Anders Nyboe

¹The Fertility Clinic, The Juliane Marie Center, Copenhagen University Hospital, Rigshopitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark
²Department of Obstetrics and Gynecology, The Juliane Marie Center, Copenhagen University Hospital, Rigshopitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark

³Correspondence address. Tel: +45-51-26-06-18; Fax: +45-35-45-49-46; E-mail: [email protected]

Submitted on December 29, 2006; resubmitted on June 4, 2007; accepted June 13, 2007

Human Reproduction 22(10):p 2707-2714, October 2007.

BACKGROUND

The purpose of this study was to assess the effect of a vanishing twin on the risk of being small-for-gestational age (SGA) in in vitro fertilization (IVF) singletons.

METHODS

The study included 642 survivors of a vanished co-twin, 5237 primary singletons and 3678 primary twins. The survivor cohort was subdivided according to gestational age at the time of vanishing to give groups of early (<8 weeks), intermediate (8–22 weeks) and late (>22 weeks) survivors.

RESULTS

The rate of SGA infants was significantly higher in survivors than in singletons (OR: 1.50, 95%CI: 1.03–2.20) and a significant inverse correlation was observed between SGA and the gestational age at the time of vanishing (r=−0.10, P < 0.02). Also in term infants, the risk of birthweight <2500 g was higher in survivors than in singletons (OR: 1.71, 95%CI: 1.06–2.74). A similar increase in the rate of low birthweight in term survivors was seen with increasing gestational age at the time of vanishing (r=−0.12; P < 0.01). In multiple logistic regression analysis adjusting for maternal age, parity, child gender and pre-eclampsia, the vanishing of a co-twin (OR: 1.56, 95%CI: 1.06–2.27) and gestational age at the time of vanishing (OR: 2.08, 95%CI: 1.00–4.35) were the only significant predictors of being SGA.

CONCULSIONS

IVF singletons with a vanished co-twin had a higher rate of SGA than singletons from a single gestation and the risk of SGA is increased with increasing gestational age at the time of vanishing.