OBJECTIVE: To estimate the effect of chorionicity on the risk of stillbirth in twins.
METHODS: A 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.
RESULTS: Data 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).
CONCLUSION: Monochorionicity has a negative effect on the in utero survival of twins, even among monochorionic-diamniotic twins without abnormalities.
LEVEL OF EVIDENCE: II
The risk of stillbirth is higher for monochorionic-diamniotic gestations compared with dichorionic-diamniotic twins at all gestational ages after 24 weeks, even among apparently uncomplicated twins.
From the Division of Maternal Fetal Medicine, Department of Obstetrics & Gynecology, Columbia University Medical Center, New York, New York.
Corresponding author: Young Mi Lee, MD, Columbia University Medical Center, Department of Obstetrics and Gynecology, Division of Maternal Fetal Medicine, 620 West 168th Street, PH 16, New York, NY 10032; e-mail: firstname.lastname@example.org.
Financial Disclosure Dr. D'Alton is a consultant for Living Micro Systems, Inc. (Watertown, MA). The other authors have no potential conflicts of interest to disclose.