Trends and Differentials in the Proximate Determinants of Fertility in Nigeria: Evidence from the 2018 and 2024 NDHS

Abstract

Nigeria’s fertility transition remains slow despite sustained investments in family planning and reproductive health interventions. Adopting Bongaarts’ proximate determinants of fertility transition, which posits that socio-economic factors influence fertility only through a limited set of biological and behavioral factors, this paper examines trends and socio-economic influence on fertility using data from the 2018 and 2024 Nigeria Demographic and Health Surveys dataset (NDHS). Adopting this framework, fertility is decomposed into four key indices: marriage (Cm), contraception (Cc), postpartum insusceptibility (Ci), and induced abortion (Ca). Findings from the NDHS show that the total fertility rate (TFR) declined modestly from 5.3 in 2018 to 4.8 in 2024, suggesting a gradual but uneven fertility transition. Substantial differences persist, with rural fertility (5.6) remaining markedly higher than urban fertility (3.9), and women with no education recorded a TFR of 6.3 compared to 3.0 among women with more than secondary education. In line with Bongaarts’ theoretical expectations, early and near-universal marriage remains the most significant exposure mechanism sustaining high fertility, with a national median age at first birth of 21.3 years (20.0 in rural areas). Postpartum insusceptibility continues to exert a significant fertility-inhibiting effect (median duration 11.9 months), particularly in northern regions. However, contraceptive use remains insufficient to produce substantial reductions in marital fertility, especially among rural, less educated, and poorer women. The induced abortion index appears to have minimal measurable impact, reflecting restrictive legal conditions and underreporting. The findings suggest that Nigeria’s fertility transition is structurally constrained by persistent early marriage and weak contraceptive uptake. Accelerating fertility decline will require multi-sectoral interventions that delay marriage, expand modern contraceptive access, and reduce entrenched regional and socio-economic inequalities to facilitate a more advanced stage of fertility transition. The study concludes that without substantial changes in these proximate determinants, particularly delayed marriage and increased contraceptive prevalence, fertility decline will remain slow. Accelerating Nigeria’s fertility transition requires integrated, multi-sectorial strategies that prioritize girl-child education, expand equitable access to modern contraceptive services, and strengthen community-based reproductive health interventions. Addressing persistent rural–urban and socio-economic inequalities is essential for accelerating the country’s fertility transition.