HOW SMALL IS TOO SMALL IN A TWIN PREGNANCY

OBJECTIVE: The objective was to determine whether small twins had a su rvival advantage with respect to small singletons after controlling fo r other factors associated with adverse perinatal outcome. STUDY DESIG N: A hospital-based cohort study included all births between 1980 and 1995 of babies born between 24 and 43 weeks' gestation. Logistic regre ssion was used to estimate the perinatal mortality risks for monochori onic and dichorionic twins with growth restriction after adjusting for gestational age, maternal age, parity, method of delivery, and the pr esence or absence of congenital malformations. RESULTS: The study samp le included 1062 dichorionic twins, 354 monochorionic twins, and 59,87 3 singletons. Small monochorionic and dichorionic twins showed a simil ar overall risk of perinatal mortality (odds ratio 1.40, confidence in terval 0.86 to 2.25). However, monochorionic twins with birth weights <10th percentile faced an increased risk of perinatal death compared w ith singletons (odds ratio 2.45, confidence interval 1.20 to 5.02). Di chorionic twins had no such increased risk (odds ratio 0.91, confidenc e interval 0.45 to 1.84). CONCLUSIONS: Twins with growth restriction a re not protected against perinatal loss, even after adjusting for cong enital malformations. In fact, monochorionic twins are more than twice as likely to die in the perinatal period as are their singleton count erparts.