Maternal–neonatal vitamin D gradient at birth in Ilorin, Nigeria: a comparative cross-sectional study

BACKGROUND: Cord-blood vitamin D concentrations at birth typically trail maternal levels, but the magnitude of this maternal-neonatal gradient and its implications for supplementation policy remains poorly characterised in sub-Saharan Africa. OBJECTIVE: To measure the absolute and relative maternal- neonatal vitamin-D gradient at birth among maternal-neonate pairs in Ilorin, North-Central Nigeria. METHODS: ELISA. Vitamin-D status was classified using exact measured serum 25(OH)D values as deficient (< 20 ng mL⁻¹), insufficient (20 to 29 ng mL⁻¹), or sufficient (≥ 30 ng mL⁻¹). Paired t-tests, Pearson correlation, McNemar χ², and one-way ANOVA were used to assess maternal-cord differences, associations, and gestational-age effects. RESULTS: Mean maternal 25(OH)D was 28.54 ± 11.01 ng mL⁻¹; while mean cord level was 24.85 ± 9.28 ng mL⁻¹, yielding an absolute gradient of 3.69 ng mL⁻¹ (95% CI 1.0-6.4; t = 2.46, p = 0.015) and a maternal: cord ratio of 1.20 ± 0.29. Concentrations were positively correlated (r = 0.498, p < 0.001). Deficiency was uncommon (2.2% in both groups), yet insufficiency affected 52.2% of mothers and 65.2% of neonates; status discordance was significant (McNemar χ² = 8.97, p = 0.003). Early pre-term neonates (28-< 32 wk) had the highest mean cord 25(OH)D concentration (29.33 ± 8.98 ng mL⁻¹), which remained below the sufficiency threshold of 30.0 ng mL⁻¹, although gestational-age differences were not statistically significant (ANOVA p = 0.19). CONCLUSIONS: A modest but clinically relevant maternal-neonatal vitamin-D shortfall persists at birth in semi-equatorial Ilorin, leaving two-thirds of neonates merely insufficient. Maternal sufficiency alone is an unreliable proxy for neonatal adequacy. CLINICAL TRIAL NUMBER: Not applicable.