Risk of fetal loss in twin pregnancies undergoing second trimester amniocentesis

OBJECTIVE: To assess the rate of fetal loss among bichorionic twin gestations undergoing genetic amniocentesis compared with singletons undergoing the procedure and untested twins. METHODS: In a retrospective cohort study, three groups were compared: 476 women with twins undergoing amniocentesis, 489 women with singleton gestations undergoing amniocentesis, and 477 women with twins presenting at a similar gestational age for ultrasound studies only. All subjects were scanned at 17-18 weeks' gestation and again approximately 4 weeks after the procedure or first ultrasound scan. Excluded were twin pregnancies after fetal reduction or chorionic villus sampling, fetuses with structural anomalies, and cases in which one fetus had died at the time of examination or after fetal reduction. RESULTS: Thirteen twin gestations in the tested group (2.73%) aborted spontaneously up to 4 weeks after the procedure compared with three twin controls (0.63%, P = .01) and three post-procedure singleton controls (0.6%, P = .01). An abnormal karyotype was discovered in 15 tested twin pregnancies (3%) and in six tested singletons (1.23%). All affected twin pairs were discordant for the chromosomal anomaly. CONCLUSION: The risk of early fetal loss in twins undergoing amniocentesis appears to be higher than that of exposed singletons or unexposed twins.