The contribution of singletons, twins and triplets to low birth weight, infant mortality and handicap in the United States.

Among multiple gestations the magnitude of neonatal mortality, morbidity and postneonatal handicap is unknown. Although the proportion of multiple births has risen dramatically during the past decade, the proportion of total births in the United States is relatively small. The vast majority of multiples are low birth weight (LBW) or very low birth weight (VLBW), conditions that magnify both short-term and long-term risks. In this study, the risks for infant mortality and for postneonatal morbidity and handicap have been calculated from race-, plurality- and birth weight-specific mortality rates from the National Infant Mortality Surveillance (NIMS) Project and birth weight-specific postneonatal handicap rates from the Office of Technology Assessment report Healthy Children in proportion to the 1988 U.S. birth cohort. U.S. health objectives for the year 2000 for race-specific birth weight and infant mortality rates were used for comparison. Compared with that of singletons, twins' and triplets' relative risks for LBW are 10.3 and 18.8, respectively. Their relative risks for VLBW are 9.6 and 32.7. Compared with singletons, twins and triplets have relative risks for infant mortality of 6.6 and 19.4, respectively. For twins and triplets, postneonatal survivors' relative risks for severe handicap are 1.7 and 2.9 while those for overall handicap are 1.4 and 2.0, respectively. Recommendations for optimizing pregnancy outcomes in multiple gestations include liberalized weight gains, reduced physical effort and early, comprehensive prenatal care.