Multiple births and outcome.

The rate of multiple-gestation pregnancies has grown exponentially over the last few decades and is responsible for the steady increase in the birth rate of low-birth weight infants. As a group, infants of multiple-gestation pregnancies have higher mortality and morbidity than singleton pregnancies. The increase in adverse outcomes is related directly to the increased risk for preterm delivery and low-birth weight, and not to the multiple gestation itself. Outcomes for multiple-gestation infants appear to be similar whether conceived spontaneously or through artificial reproductive technology. Efforts to reduce the birth rate of low-birth weight infants should target multiple-gestation pregnancies.