The risk of repeating low birth weight and the role of prenatal care.

OBJECTIVE

To estimate the influence of adequacy of prenatal care and other known risk factors on the risk of repeating low birth weight (LBW) (less than 2500 g).

METHODS

This was a retrospective cohort study of women having two births in Washington state during 1984-1990, as recorded using linked birth certificate records. Logistic regression was used to control for maternal age, marital status, smoking, miscarriage, inter-pregnancy interval, and prenatal care.

RESULTS

Compared to the reference group of women with normal-weight first births (at least 2500 g), women with LBW first births, either preterm or small for gestational age (SGA), were significantly more likely to have an LBW second birth. The estimated relative risk of repeating LBW in general was 7.0 (95% confidence interval 4.8-10.1). Smoking during the second pregnancy was a significant effect modifier. The risk estimates were not significantly affected by any of the other variables entered into the models, including adequate prenatal care.

CONCLUSIONS

Prior delivery of a preterm or SGA LBW infant was the strongest predictor of LBW delivery in a subsequent pregnancy. Adequate prenatal care during the second pregnancy did not provide statistically significant protection against the risk of repeat LBW. The tendency for women to have repeat LBW deliveries despite adequate prenatal care indicates a need for a better understanding of the underlying pathophysiology of preterm and SGA delivery.