Short interpregnancy interval: a risk factor for low birthweight.

In a prospective study of 1683 women delivering at Yale-New Haven Hospital during 1980 through 1982, those conceiving within 1-4 months of a prior live birth were at increased risk of delivering a low birthweight (less than 2500 gm) newborn (RR = 5.70, 95% Cl = 0.83, 39.75), as were those conceiving 5-8 months later (RR = 3.25, 95% Cl = 1.02, 10.34), when compared with women conceiving 9 or more months later. Adjustment was made for maternal age, ethnicity, preterm delivery or low birthweight of prior newborn, and cigarette smoking in pregnancy. Gestational age of the second delivery was not affected by interpregnancy interval. These results may explain earlier reports of increased perinatal mortality after short birth intervals.