• Young Mi Lee, Blair J Wylie, Lynn L Simpson, and Mary E D'Alton.
• Division of Maternal Fetal Medicine, Department of Obstetrics & Gynecology, Columbia University Medical Center, New York, New York 10032, USA. yml9002@med.cornell.edu
• Obstet Gynecol. 2008 Feb 1;111(2 Pt 1):301-8.

ObjectiveTo estimate the effect of chorionicity on the risk of stillbirth in twins.MethodsA retrospective cohort analysis was performed of all twin deliveries of at least 24 weeks of gestation at a single tertiary care center from December 2000 to May 2007. The risk of fetal death with advancing gestation was calculated for monochorionic-diamniotic twins and for dichorionic-diamniotic twins. Overall in utero survival was compared by using Kaplan-Meier analysis and a hazards ratio with 95% confidence intervals estimated to assess the degree of difference. Pregnancies affected by growth abnormalities, anomalies, or twin-twin transfusion syndrome were subsequently excluded and survival by chorionicity similarly compared within these "apparently normal" gestations.ResultsData from 1,000 consecutive twin pairs (196 monochorionic-diamniotic twins and 804 dichorionic-diamniotic twins) were analyzed. Stillbirths occurred in seven (3.6%) monochorionic-diamniotic and nine (1.1%) dichorionic-diamniotic twin pairs. Monochorionic-diamniotic twins had a higher risk of stillbirth compared with dichorionic-diamniotic twins, both overall (log-rank P=.004) and at each gestational age after 24 weeks, with this risk persisting in the subset of 771 (130 monochorionic-diamniotic twins and 641 dichorionic-diamniotic twins) "apparently normal" twins (log-rank P=.039).ConclusionMonochorionicity has a negative effect on the in utero survival of twins, even among monochorionic-diamniotic twins without abnormalities.Level Of EvidenceII.

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