Weight gain and spontaneous preterm birth: the role of race or ethnicity and previous preterm birth

OBJECTIVE: To study how the relationship between gestational weight gain and spontaneous preterm birth interacts with maternal race or ethnicity and previous preterm birth status. METHODS: This was a retrospective cohort study of singleton births to women of normal or low prepregnancy body mass index. Gestational weight gain was measured as total weight gain divided by weeks of gestation at delivery, and weight gain was categorized as low (less than 0.27 kg/wk,), normal (0.27-0.52 kg/wk), or high (more than 0.52 kg/wk). Univariable and multivariable analyses were performed on the relationship between weight gain categories and spontaneous preterm birth, stratified by maternal race or ethnicity and history of previous preterm birth. RESULTS: Overall, low weight gain was associated with spontaneous preterm birth (adjusted odds ratio AOR] 2.5, 95% confidence interval CI] 2.0-3.1). Although low gain was consistently associated with increased spontaneous preterm birth, some differences were found in subgroup analysis. Among African Americans with a previous preterm birth, both low and high weight gain were associated with increased odds of spontaneous preterm birth (AOR for low weight gain 4.3, 95% CI 1.2-15.5; AOR for high weight gain 6.1, 95% CI 1.8-20.2). For all other groups, high weight gain was not associated with spontaneous preterm birth. Among Asians with a previous preterm birth, low weight gain was not statistically significantly associated with spontaneous preterm birth (AOR 1.9, 95% CI 0.5-7.7). Among Asians there was also a non-statistically significant inverse relationship between high weight gain and spontaneous preterm birth (AOR 0.5, 95% CI 0.3-1.1). CONCLUSION: These results confirm an association between low maternal weight gain and spontaneous preterm birth. The effect modification of maternal race or ethnicity and history of previous preterm birth on this association deserves further study. LEVEL OF EVIDENCE: II-2.