There is disparity in fertility level across the six geopolitical zones in Nigeria. Deeper uunderstanding about the drivers of fertility trends are necessary to prioritize zonal specific strategies for fertility reduction in Nigeria. Thus, this study examined the proximate determinants (PDs) of fertility and decomposed the change in its level across the six geo-political zones in Nigeria. Data from Nigeria Demographic and Health Surveys of 2003 and 2018 were analyzed. Fertility data were based on the report of full birth history from women of reproductive age. The Revised Bongaarts framework was used to estimate PDs and fertility levels. The contribution of each PDs to the observed changes in fertility levels was quantified using Das Gupta's five- factor decomposition method. The Total fertility rate (TFR) in 2003 and 2008 across the zones are South-South (5.04 vs 4.36), South-West (4.88 vs 4.26), North West (7.25 vs 6.85), North East (6.87 vs 6.54), North Central (5.72 vs 5.48), South East (5.06 vs 4.86), Nigeria (6.00 vs 5.59). Across the zones, there was a change in the fertility inhibiting effect of Contraception (Cc) between 2003 and 2018. The fertility inhibiting effect of Postpartum Infecundability (Ci) and Abortion was the highest and smallest respectively across the zones. Delayed sexual exposure (Cm) and contraceptive use (Cc) contributed the most to the change across the regions. The percentage contribution of Cm in South-South, South West, and South East was 87.04%, 52.89%, and 172.85% respectively. Furthermore, most of the fertility change observed in North Central was attributable to Cc. Abortion index was not an important inhibiting factor of fertility in Nigeria. Delayed sexual exposure and contraceptive use accounted for the largest change observed in fertility levels across the six geo-political zones in Nigeria between 2003 and 2018. Strategies that promote delayed sexual exposure, contraceptive use and breast feeding practices will enhance fertility transition in Nigeria.
Keywords: Nigeria; Proximate determinants; change in fertility level; decomposition.