Prevalence of short inter-birth intervals and associated factors among women of reproductive age: evidence from a nationally representative survey in Tanzania

Introduction Short inter-birth intervals negatively impact maternal and child health; however, data on their prevalence and associated factors in Tanzania are limited. This study investigates the prevalence of short inter-birth intervals and the associated factors among women of reproductive age in Tanzania. Methods This was a cross-sectional study utilizing the 2022 Tanzania Demographic and Health Survey and Malaria Indicator Survey dataset. The study population included women aged 15-49 years with at least two births within five years preceding the survey. A short inter-birth interval was defined as a birth occurring < 33 months after the preceding birth. A generalized linear model with Poisson as a link and robust standard errors was used to examine factors associated with short inter-birth intervals. A p-value < 0.05 was considered statistically significant. Results A total of 8,350 births from 6,034 women were included in this analysis. The mean (+/- SD) age of the women was 31.6 +/- 6.8 years. The overall prevalence of short inter-birth intervals was 42.6%. Younger age (aPR 3.12, 95% CI 2.88-3.52 for age 15-24 years, and aPR 1.74, 95% CI 1.62-1.1.86 for age 25-34 years), being married (aPR 1.27, 95% CI 1.03-1.57), late age at first childbirth (aPR 1.24, 95% CI 1.17-1.32) for a 20-24 years and aPR 1.55, 95% CI 1.39-1.73 for >= 25 years), and higher birth order (aPR 1.02, 95% CI 1.03-1.19; aPR 1.24, 95% CI 1.14-1.34; aPR 1.72, 95% CI 1.58-1.86 for 3rd, 4th, and 5th or more birth orders, respectively, compared to 2nd birth order) were independently associated with short inter-birth intervals. Additionally, there was significant variation in the prevalence of short inter-birth intervals across different zones and levels of household wealth. Women from richer (aPR 0.87, 95% CI: 0.80-0.95) and richest (aPR 0.84, 95% CI: 0.74-0.94) households exhibited a lower prevalence of short inter-birth intervals. Conclusion This study highlights the significant prevalence of short inter-birth intervals among women of reproductive age in Tanzania. The associated factors include younger age, marital status, delayed first childbirth, higher birth order, geographical disparities, and lower household wealth. These findings highlight the need for targeted interventions to promote birth spacing and improve maternal and child health outcomes.