Determinants of Short Birth Intervals among married women in Karachi, Pakistan

Introduction Birth spacing is a critical pathway to improving reproductive health. The World Health Organization recommends a minimum of 33-month interval between two consecutive births to reduce maternal, perinatal, and infant morbidity and mortality. Our study evaluated factors associated with short birth intervals (SBIs) of less than 33 months between two consecutive births, in three peri-urban municipalities in Karachi, Pakistan. Methods We used data from a cross-sectional study among married women of reproductive age (MWRA) who had at least one live birth in the six years preceding the survey (N=2394). Information regarding their sociodemographic characteristics, reproductive history, fertility preferences, family planning history, and a six-year reproductive calendar were collected. To identify factors associated with SBIs, we fitted simple and multiple Cox-proportional hazards models and computed hazard ratios (HR) with their 95% confidence intervals (CI). Results The median birth interval was 25 months (IQR: 14-39 months), with 22.9% of births occurring within 33 months of the index birth. Women’s increasing age [25-29 years (aHR=0.64, 95% CI: 0.54-0.77), 30+ years (aHR=0.30, 95% CI: 0.23-0.40) compared to <25 years]; secondary education [aHR 0.78. 95% CI: 0.65-0.93], intermediate education [aHR 0.63, 95% CI: 0.49-0.82], higher education (aHR=0.71, 95% CI: 0.53-0.96) compared to no education, and a male child of the index birth (aHR=0.79, 95% CI: 0.68-0.92) reduced the likelihood of SBIs. Women’s younger age <20 years [aHR 1.32, 95% CI 1.03-1.70] compared to 20-24 years, and those who did not use contraception within 9-months of the index birth had a higher likelihood for SBIs for succeeding birth compared to those who used contraception (aHR=2.33, 95% CI: 2.01-2.70). Conclusion This study evaluates factors associated with birth spacing practices among married women of childbearing age in urban settlements of Karachi. Our study shows that birth intervals in the study population are lower than the national average. To optimize birth intervals, programs should target child spacing strategies and counsel MWRA on the benefits of optimal birth spacing, family planning services and contraceptive utilization. Ethics The study received ethical approval from the Ethical Review Committee (ERC) at the Aga Khan University (AKU) (4964-Ped-ERC-17) and the Institutional Review Board (IRB) at the Harvard T.H. Chan School of Public Health (IRB17-1864). Informed written consent was obtained from each study participant. Women who were unable to sign provided consent with a thumb impression in the presence of witnesses. Strengths and limitation This is the first study that has investigated birth spacing in urban areas of Karachi, Pakistan It is a cross sectional study that has employed a three-stage random sampling design i.e. at cluster level, at household level, and at individual level. Participants were selected from low-income areas of Karachi, therefore not representative of metropolitan population of Karachi. There may be an underrepresentation of birth intervals because the study did not consider abortions or miscarriages. The study only considered births in six-year calendar time and therefore births occurred before or after this calendar time were considered as no-event. There may be underestimation in birth intervals where women did not give birth since her last-born in this six-year calendar time.