Growth retardation, size at birth and perinatal mortality in twin pregnancy.

The records of 194 consecutive pairs of twins were reviewed. Univariate and multivariate analyses of relative risks (RR) of perinatal death were performed. Perinatal mortality rate was higher in small-for-gestational-age twins and in fetuses with discordancy in size at birth more than 20% and 25%. The RR of perinatal death for small-for-gestational-age twins was 4.8 (2.74-8.42 95% CI). For intertwin birth-weight percent differences of 20% and 25%, the RR was 5.48 (3.2-9.38 95% CI) and 7.2 (3.87-13.42 95% CI). Population mortality attributable risk in the two populations (10.36% and 14.5%, respectively) demonstrates the importance of the prenatal assessment of the respective size of twins in preventing perinatal death.