Effect of Interpregnancy Interval on Infant Low Birth Weight: A Retrospective Cohort Study Using the Michigan Maternally Linked Birth Database

Objective: To examine the relationship between interpregnancy interval and low birth weight (LBW), using the retrospective cohort design. Methods: We used the maternally linked Michigan livebirth data documented between 1989 and 2000 to evaluate LBW in relation to interpregnancy (i.e., delivery-to-conception) interval, overall and at levels of other reproductive risk factors. We fit separate logistic regression models for pairs of first-second, second-third, third-fourth, and fourth-fifth births to control for confounding. Results: Of the 565,911 infants identified, 5.5% had LBW. Univariate and stratified analyses showed that the risk for LBW was lowest when the interpregnancy interval was 18–23 months, and increased with shorter or longer intervals. This J-shaped relationship persisted after controlling for all risk factors simultaneously. For example, among the first-second birth pairs, the adjusted odds ratios (AORs) for LBW associated with interpregnancy intervals <6, 24–59, 60–95, and 96–136 months were 1.4 (95% confidence interval [CI] = 1.3–1.5), 1.5 (95% CI = 1.3–1.6), 1.1 (95% CI = 1.0–1.1) and 1.5 (95% CI = 1.3–1.8), respectively, compared with an interval of 18–23 months. Among the second-third birth pairs, the AORs were 1.5 (95% CI = 1.3–1.6), 1.3 (95% CI = 1.2–1.4), 1.1 (95% CI = 1.0–1.1), and 1.6 (95% CI = 1.3–2.0), respectively. Among the third-fourth birth pairs, the AORs were 1.2 (95% CI = 1.1–1.4), 1.3 (95% CI = 1.1–1.5), 1.0 (95% CI = 0.9–1.1), and 1.4 (95% CI = 1.0–2.0), respectively. Among the fourth-fifth birth pairs, the AORs were 1.3 (95% CI = 1.1–1.6), 1.2 (95% CI = 0.9–1.5), 1.1 (95% CI = 1.0–1.4), and 1.3 (95% CI = 0.8–2.3), respectively. The population attributable risk associated with interpregnancy intervals shorter than 18 months or longer than 23 months was 9.4%. Conclusion: These data suggest that spacing pregnancies appropriately could be used as a strategy for preventing LBW.