The relationship of interpregnancy interval to the risk of preterm births to black and white women

Background Premature births are of major public health concern. Short interpregnancy intervals may influence the incidence of premature births among black and white women, with blacks conceiving at shorter intervals than whites. Design Women (293 blacks and 468 whites) with complete obstetric records delivering singleton infants between January 1988 and December 1993 were included. We related the outcome of the second of any pair of consecutive pregnancies to the interval between the pair. Results Both black and while women conceiving within 3 months or less of their preceding pregnancy had a high risk of premature birth (37.5%). At all other intervals, the risk among blacks was consistently over twice that for whites. Conception within an interval of 6 months or less was significantly associated with increased risk of premature birth for blacks (35.8% versus 25.8% for longer intervals; P = 0.03), but this difference was not significant after controlling for other confounding variables (odds ratio = 1.52, 95% confidence interval [CI] : 0.91-2.55). Whites conceiving within 6 months compared to those conceiving after more than 6 months had no significant increased risk (18.4% versus 9.7%). The risk of preterm birth was 1.67 (CI : 0.42-2.91) for women conceiving at less than or equal to 6 months, compared to those who conceived after 6 months, after controlling for confounding variables. Conclusions Preterm birth was not significantly associated with short intervals of 6 months or less for both black and white women. A subset of multiparous black women with short interpregnancy intervals, however, may have an increased risk of premature birth.