Determinants of Suboptimal Birth Interval in Ugandan Women of Reproductive Age: A Generalized Linear Model Approach Using Modified Poisson Regression Analysis

Background Optimal birth spacing is critical for maternal and child health, with the World Health Organization recommending pregnancy intervals of at least 24 months to minimize adverse health outcomes. Despite global progress in family planning, suboptimal birth intervals remain persistently high in sub-Saharan Africa, particularly in Uganda, where high fertility rates and unmet contraceptive needs continue to compromise maternal and child wellbeing. This study estimated the prevalence and determinants of suboptimal birth intervals among Ugandan women over a two-decade period. Methods This study utilized data from five consecutive Uganda Demographic and Health Surveys conducted in 2000/2001, 2006, 2011, 2016, and 2022. The analytical sample comprised 28,319 women of reproductive age with at least two live births. Suboptimal birth interval was defined as spacing less than 33 months between consecutive births, following WHO recommendations. Modified Poisson regression with robust variance estimation was employed to estimate prevalence ratios and 95% confidence intervals for socio demographic, economic, reproductive health, and temporal factors associated with suboptimal birth spacing, accounting for the complex survey design. Results Overall, 84% of Ugandan women experienced at least one suboptimal birth interval, with prevalence declining from 88.3% in 2000 to 79.2% in 2022. High parity (≥ 4 children) emerged as the strongest predictor, with women experiencing 47% higher prevalence of suboptimal intervals compared to those with fewer children. Women with secondary and higher education had 5% and 11% lower prevalence respectively compared to uneducated women, while those in the highest wealth quintile experienced 5% lower prevalence than the poorest. Rural residence conferred 4% higher prevalence compared to urban areas, and women aged 15–24 years had 12% higher prevalence than older age groups. Desire for more than five children and use of traditional contraceptive methods were associated with increased prevalence, while temporal trends showed consistent improvements, with 9% lower prevalence in 2022 compared to 2000, coinciding with increased modern contraceptive use from 22.4% to 37.1%. Conclusion Suboptimal birth intervals remained persistently high among Ugandan women throughout the two-decade study period, though modest declining trends were observed. Key determinants included high parity, lower socioeconomic status, rural residence, younger maternal age, and desire for large families. Multi-level interventions are urgently needed to address both supply-side barriers through expanded access to modern contraceptives and demand-side factors through culturally sensitive family planning counseling, male partner engagement, and community education.