Assessing the effects of duration of birth interval on adverse pregnancy outcomes in sub-Saharan Africa: a propensity score-matched analysis

OBJECTIVES: Unlike high-income countries, sub-Saharan African countries have the highest burden of adverse pregnancy outcomes such as abortion, stillbirth, low birth weight and preterm births. The WHO set optimal birth spacing as a key strategy to improve pregnancy outcomes. Estimating the impact of short and long birth intervals on adverse pregnancy outcomes based on an observational study like the Demographic and Health Survey (DHS) is prone to selection bias. Therefore, we used the propensity score-matched (PSM) analysis to estimate the actual impact of short and long birth intervals on adverse pregnancy outcomes. DESIGN: A community-based cross-sectional study was conducted based on the DHS data. SETTING: We used the recent DHS data of 36 sub-Saharan African countries. PARTICIPANTS: A total of 302 580 pregnant women for stillbirth and abortion, 153 431 for birth weight and 115 556 births for preterm births were considered. PRIMARY OUTCOME MEASURES: To estimate the impact of duration of birth interval (short/long) on adverse pregnancy outcomes, we used PSM analysis with logit model using psmatch2 ate STATA command to find average treatment effect on the population (ATE), treated and untreated. The quality of matching was assessed statistically and graphically. Sensitivity analysis was conducted to test the robustness of the PSM estimates using the Mantel-Haenszel test statistic. RESULTS: The prevalence of short and long birth intervals in sub-Saharan Africa was 46.85% and 13.61%, respectively. The prevalence rates of abortion, stillbirth, low birth weight, macrosomia, and preterm births were 6.11%, 0.84%, 9.63%, 9.04%, and 4.87%, respectively. In the PSM analysis, the differences in ATE of short birth intervals on abortion, stillbirth, low birth weight, and preterm births were 0.5%, 0.1%, 0.2%, and 0.4%, respectively, and −2.6% for macrosomia. The difference in ATE among the treated group was 1%, 1%, and 1.1% increased risk of abortion, low birth weight, and preterm births, respectively, while there was no difference in risk of stillbirth between the treated and control groups. The ATEs of long birth intervals on abortion, stillbirth, low birth weight, macrosomia and preterm births were 1.3%, 0.4%, 1.0%, 3.4%, and 0.2%, respectively. The ATE on the treated group had 0.9%, 0.4%, 2.4%, 2.8%, and 0.2% increased risk of abortion, stillbirth, low birth weight, macrosomia, and preterm births, respectively. The estimates were insensitive to hidden bias and had a good quality of matching. CONCLUSION: Short and long birth intervals had a significant positive impact on stillbirth, abortion, low birth weight, macrosomia and preterm births after matching treated and control groups by observed variables. These findings highlighted maternal and newborn healthcare programmes and policies to empower reproductive-aged women to exercise optimal birth spacing to reduce the incidence of stillbirth, abortion, low birth weight, macrosomia and preterm births.