The influence of maternal age on optimal interbirth intervals prevalence among women of reproductive age in North-East Nigeria

Optimal interbirth interval (OBI), defined as an interval of at least 33 months between consecutive live births, is associated with improved health outcomes for both mothers and children. The North-East region of Nigeria continues to experience suboptimal birth spacing, influenced by complex socio-economic, cultural, and healthcare access factors. This study examined the influence of age and other determinants on the achievement of optimal interbirth interval among women of reproductive age in this region. A cross-sectional analysis was conducted using data from the 2018 Nigeria Demographic and Health Survey (NDHS). The study sample comprised 4,884 women aged 15–49 years from six northeastern states. The primary outcome was optimal interbirth interval (≥ 33 months), coded as 1, compared to short interval (< 33 months), coded as 0. The primary exposure variable was age. Descriptive statistics and bivariate analyses were performed to characterize the prevalence of SBI according to sociodemographic factors. Multivariable logistic regression was used to assess the association between age and SBI, after adjusting for other predictors. Older women, particularly those aged 35–39, exhibited the highest prevalence of optimal interbirth interval. The prevalence of OBI increased with advancing age, while younger women (15–19 years) had significantly lower rates. Multivariable analysis revealed that older age was protective against SBI, with women aged 35–39 having significantly lower odds (AOR: 5.09; 95% CI: 2.50-10.35). State-level disparities were observed, with Borno and Gombe having the highest prevalence rates. Age significantly influences the likelihood of achieving optimal interbirth interval in Northeast Nigeria, with younger women being less likely to attain optimal spacing. Targeted interventions focusing on reproductive health education and access to contraception for young women, along with state-specific programs, are crucial for improving birth spacing and maternal health outcomes in the region.