ImportanceThe interpregnancy intervals are suboptimal worldwide, and women lack access to high-quality postpartum contraceptive services in China.ObjectiveTo evaluate the effectiveness of integrating postpartum contraceptive interventions into the existing maternal and child health care (MCH) system.Design, Setting, and ParticipantsThis cluster randomized trial randomly allocated 13 communities in Minhang District in Shanghai, China, to the intervention or the control group. Data were collected between September 2020 and February 2023. Eligible participants included women who registered their pregnancy in community health centers and were followed up to 1 year post partum. Data analysis was conducted from April 2023 to May 2024.InterventionsParticipants in the intervention group received postpartum contraception consultations, online educational videos, a 45-minute class, health prescriptions, and educational pamphlets at 5 stages in alignment with the MCH system of China. The control group received routine MCH services.Main Outcomes and MeasuresThe primary outcome was incidence of unintended pregnancy within 1 year after childbirth. The secondary outcomes included knowledge level of postpartum contraception, utilization rate of reliable long-acting reversible contraception (LARC), and incidence of induced abortion.ResultsA total of 1279 participants (698 in intervention from 7 clusters and 581 in control from 6 clusters) were recruited, and 995 (521 older than 30 years [40.7%]; 539 intervention [54.2%] and 456 control [45.8%]) completed the trial. The incidence of unintended pregnancy, LARC utilization, and induced abortion within 1 year after childbirth was 1.5% (8 participants), 3.2% (17 participants), and 0.6% (3 participants), respectively, in the intervention group, and 3.9% (18 participants), 1.1% (5 participants), and 2.0% (9 participants), respectively, in the control group. Participants in the intervention group were significantly less likely to experience unintended pregnancy (adjusted odds ratio [aOR], 0.33; 95% CI, 0.16-0.70), had a higher rate of LARC utilization (aOR, 2.47; 95% CI, 1.02-5.98), and a lower rate of induced abortion due to unintended pregnancy (aOR, 0.30; 95% CI, 0.09-0.99). The postpartum contraception knowledge level in the intervention group was substantially higher than the control group (β = 24.20; 95% CI, 20.92-27.47).Conclusions and RelevanceThis cluster randomized clinical trial demonstrated the designed postpartum contraceptive interventions were effective in reducing unintended pregnancy and induced abortion and increasing postpartum contraception knowledge and LARC utilization among women at 1-year post partum.Trial RegistrationChictr.org.cn Identifier: ChiCTR2000034603