Low birth weight in relation to the interval between pregnancies.

Abstract

Regarding the article by Rawlings et al. (Jan. 12 issue) we wonder whether a short interpregnancy interval might be confounded by factors that were not considered in the analysis. Although all the women studied were drawn from military families with access to high-quality health care no information was provided about the proportion of mothers who worked and what types of occupations they had. Since it has previously been shown that physical exertion associated with employment in the Army may increase the risk of preterm delivery might a racial difference in employment patterns account to some extent for the increased risk of preterm birth among the Black women in the sample? The large racial difference in the prevalence of low birth weight or preterm delivery among women with interpregnancy intervals of 3 to 5.9 months also deserves comment. It is puzzling to find that this interpregnancy interval has such a disparate effect among Black women as compared with White women when no marked racial difference is apparent at shorter or longer intervals. Nonetheless the presence of a racial difference associated with even one interpregnancy interval suggests that short intervals themselves cannot wholly explain the racial disparity in pregnancy outcomes. Also noteworthy is the fact that interpregnancy intervals of less than nine months are associated with poor outcomes among Black women whereas only the shortest intervals (less than three months) are disadvantageous for White women. The authors report in addition that the adverse effect of a short interpregnancy interval was strongest when the preceding pregnancy resulted in a low-birth-weight or preterm infant. These findings are interesting and merit additional discussion. (full text)