Factors associated with repetition of low birthweight: Missouri longitudinal study.

The tendency to repeat low birthweight (LBW < 2500 g) was studied in 182,285 linked first and second birth Missouri livebirths for 1978-90, of which 10,701 had first birth LBW. We examined the likelihood of LBW repetition by first birth birthweight, preterm delivery, and small-for-gestational-age (SGA) status by race, and the odd ratios (ORs) of repeat LBW for risk factors such as smoking, in comparison with ORs of second birth LBW among women with normal-weight first births. We found a strong tendency to repeat LBW (21%), especially following more extreme LBW first births. Adjusted ORs for repeat LBW were 10.1 for births that were preterm and SGA; 7.9 for preterm non-SGA; and 6.3 for SGA term births. Significant ORs of LBW repetition were found for smoking (1.52 and 1.85 for smoking in second pregnancy only and both pregnancies, respectively), short interpregnancy interval (1.33), and advanced maternal age (1.17), but the ORs were generally lower than those for women with normal-weight first births. Low pre-pregnancy weight was a significant risk factor for LBW repetition.