Objective:To explore the influence of interpregnancy interval (IPI) on pregnancy complications in multiparas.Methods:This was a retrospective cohort study involving 7 669 singleton parturients who delivered at ≥28 gestational weeks in the Affiliated Hospital of Southwest Medical University between December 2015 and December 2020 and had given birth in the third trimester before. Clinical data were collected, including the baseline characteristics, pregnancy complications, gestational weeks at delivery, and neonatal birth weight. According to the IPI, these women were divided into five groups: <12 months ( n=350), 12-<24 months ( n=945), 24-<60 months ( n=2 544), 60-<120 months ( n=2 478), and ≥120 months ( n=1 352). Based on the recommendation of the World Health Organization, pregnant women with an IPI of 24-<60 months were the control group. A multivariate logistic model was used to adjust for confounders and calculate the risks of pregnancy complications, including gestational diabetes mellitus (GDM) and hypertensive disorders of pregnancy (HDP). The influences of maternal age and previous delivery mode on the associations between IPI and maternal complications were analyzed. Analysis of variance (ANOVA), Chi-square test, and Cochran-Mantel-Haenszel Chi-square test were used for statistical analysis. Results:Compared with the control group, the incidence of GDM and HDP increased in the 60-<120 months group ( OR=1.23, 95% CI: 1.01-1.48 and OR=1.47, 95% CI: 1.13-1.92) and ≥120 months group ( OR=1.37, 95% CI:1.07-1.78 and OR=1.92, 95% CI: 1.39-2.64); the risks of uterine rupture/postpartum hemorrhage and placental abruption increased in the <12 months group ( OR=1.54, 95% CI: 1.01-2.34) and 12-<24 months group ( OR=2.38 95% CI: 1.13-5.02), respectively. In the 60-<120 months group, the risk of GDM increased only in non-elderly women (adjusted OR=1.71, 95% CI: 1.36-2.14), so did the risks of GDM and HDP in the ≥120 months group (adjusted OR=3.11, 95% CI: 2.10-4.62 and adjusted OR=1.81, 95% CI: 1.12-2.91). Among women who had undergone a previous cesarean section, the risk of GDM increased in the ≥120 months group (adjusted OR=1.35, 95% CI: 1.00-1.81). In the 60-<120 months group and ≥120 months group, the risk of HDP increased in postpartum women (adjusted OR=1.79, 95% CI: 1.08-2.95 and adjusted OR=3.32, 95% CI: 1.91-5.77). Conclusion:IPI≥60 months is a risk factor for GDM and HDP, and the associations between IPI and maternal complications are influenced by maternal age.