The relationship of interpregnancy interval to infant birthweight and length of gestation among low-risk women, Georgia

To examine the association between interpregnancy interval and low birthweight (< 2500 g), preterm delivery (< 37 weeks' gestation), and inadequate fetal growth, we studied a population-based sample of 23 388 white and 4885 black women at low risk for adverse pregnancy outcomes who delivered their first and second infants in Georgia from 1980 to 1992. We used fetal death and livebirth certificates. The interpregnancy interval was the time from delivery to the woman's next conception. For each pregnancy outcome, we stratified by race and used logistic regression to assess the association between interpregnancy interval and outcome, while controlling for confounders. Intervals < 6 months were observed for 3.7% of white women and 7.0% of black women and intervals greater than or equal to 48 months were seen for 16.8% of white women and 24.8% of black women. Results from logistic regression showed that, for both races, interpregnancy interval was associated with low birth-weight and preterm delivery. Nearly all of the increased risk occurred in intervals < 6 months or greater than or equal to 48 months. The magnitude of the increase in risk associated with these intervals ranged from modest to moderate and was similar for black and white women. Because short interpregnancy intervals are rare and are weak risk factors among low-risk women, efforts to lengthen interpregnancy intervals are unlikely to reduce substantially their rates of adverse pregnancy outcomes.