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Objective: To examine the influence of interpregnancy interval on the elevated risk of term small for gestational age (SGA) births to black women.

Methods: This study is a secondary analysis of data from the Delivery Interview Program, a hospital-based cohort study of 12,718 women conducted at the Boston Hospital for Women from 1977 to 1980. The current analysis was limited to black and white parous women who gave birth to term infants during the study and whose last previous pregnancies had also resulted in term, live births. There were 578 black and 3400 white women who met these criteria. The rates of term SGA births for black and white women were calculated according to six interpregnancy intervals (6 or less, 6-12, 12-24, 24-36, 36-60, or longer than 60 months). Multiple logistic regression was used to control for confounding.

Results: The overall rate of term SGA births was 6.4% for black women compared with 3.9% for white women (relative risk [RR] 1.7, 95% confidence interval [CI] 1.2, 2.4). Black women were also more likely than white women to have interpregnancy intervals of 6 months or less (9.2% black, 4.8% white; RR 1.9, 95% CI 1.4, 2.6). At every interpregnancy interval, black women had a higher rate of term SGA births than white women. After controlling for interpregnancy interval in a logistic regression analysis, the increased risk of SGA delivery among black women remained unchanged (odds ratio 1.7, 95% CI 1.1, 2.5).

Conclusion: Although black women were more likely than white women to have SGA births and short interpregnancy intervals, differences in interpregnancy intervals between the races did not explain the disparity in term SGA births.

(C) 1999 The American College of Obstetricians and Gynecologists