Decomposition of Fertility Change in Nigeria from the 2018 to the 2023–24 NDHS Using Proximate Determinants and Contextual Socioeconomic Shifts with Microdata

Nigeria’s total fertility rate declined from 5.3 children per woman in the 2018 Nigeria Demographic and Health Survey to 4.8 in the 2023-24 NDHS [1]reflecting gradual demographic transition in a population exceeding 237 million. Microdata analysis yields closely aligned estimates of 5.24 to 4.74. Quantifying drivers of this change supports policies for harnessing the demographic dividend toward sustainable economic development. This study decomposes fertility change between the two NDHS rounds, focusing on TFR and age-specific fertility patterns. It applies the Bongaarts proximate determinants framework as the primary method, partitioning fertility into multiplicative effects of marriage patterns (proportion ever married, age at first marriage), postpartum infecundability (influenced by breastfeeding), contraception (modern method use, unmet need), and abortion (indirectly inferred as a residual component), with regression-based extensions to assess associations with female education and urban residence. Analyses use publicly accessible NDHS microdata (individual recode and birth recode files from both rounds, available via The DHS Program after registration and approval), incorporating complex survey design features (sampling weights, clustering, stratification) to ensure representative estimates. Decomposition identities inherent in the Bongaarts framework facilitate rigorous quantification of each determinant's fertility-reducing impact. A decline in Ci implies longer postpartum infecundability and stronger fertility inhibition, since Ci is inversely related to the mean duration i (39%, reflecting longer average amenorrhea/breastfeeding durations, potentially due to compositional shifts or improved child health practices amid urbanization). This counterintuitive pattern relative to typical urbanization effects warrants subgroup analysis (e.g., urban vs. rural durations), increased effective contraceptive use (36%, modern prevalence rising from 11.5% to 14.6% among in-union women), and shifts toward lower marriage exposure (21%). The residual component was small (4%). Expected patterns based on observed differentials suggest that increased female education and urbanization contribute substantially to the decline, consistent with rural-urban differentials (rural TFR 5.6 vs. urban 3.9 in the 2023–24 NDHS Key Indicators Report). Proximate determinants, particularly modest rises in modern contraceptive prevalence (12% to 15% among married women) and satisfied demand (to 37%), appear complementary, though postpartum factors warrant careful measurement among women at pregnancy risk. Results will highlight leverage points for accelerating transition, e.g., enhancing education access and family planning services while informing innovative, data-driven strategies for population management and economic resilience. By leveraging newly available 2023–24 NDHS microdata, this work aligns with established decomposition approaches in demographic literature and contributes evidence-based insights for sustainable development in Nigeria.