Association of interpregnancy interval with hypertensive disorders of pregnancy: a retrospective cohort study.

OBJECTIVE: The optimal interpregnancy interval (IPI) for preventing hypertensive disorders of pregnancy (HDP) remains unclear, and whether this association is modified by maternal baseline characteristics has not been well established. This study aimed to evaluate the association between IPI and the risk of HDP and to examine potential effect modification by maternal characteristics. METHODS: This retrospective cohort study included 1,633 women with at least two consecutive singleton deliveries between 2014 and 2023. IPI was modeled as a continuous variable in regression analyses. Modified Poisson regression with robust variance was applied to estimate risk ratios (RRs) and 95% confidence intervals (CIs) for HDP and preeclampsia. Subgroup and sensitivity analyses were performed to assess effect modification and the robustness of the findings. No statistically significant interaction was observed for maternal age or pre-pregnancy BMI. Sensitivity analyses demonstrated consistent results across multiple scenarios, including additional adjustment for aspirin use. CONCLUSION: Longer IPI was independently associated with a modest increase in the risk of HDP, particularly among women without prior HDP. No significant association was observed for preeclampsia, suggesting that IPI may primarily influence the broader HDP phenotype rather than specific subtypes. These findings support the consideration of IPI in preconception counseling, with an emphasis on individualized risk assessment.