A decade-long assessment reveals persistent vitamin D deficiency and its associated factors in early-pregnant women from northern China (2016-2025).

BACKGROUND: Large-scale data on vitamin D status in early-pregnant women in high-risk Northern China are scarce. This study evaluated the decadal trends (2016-2025) and associated factors of serum 25(OH)D levels in this population in Shanxi Province. METHODS: This retrospective cohort included 20,693 early-pregnant women (<14 weeks). Serum 25(OH)D was measured. Logistic regression assessed associations with of season, age, conception mode, and the COVID-19 period. RESULTS: The median 25(OH)D was 36.12 nmol/L, indicating a concerning status. Season was the strongest associated factor. The pandemic period (2020-2022) saw a significant rise in severe deficiency (<30 nmol/L) to 35.6%. Advanced maternal age (≥35) and ART conception were linked to higher levels. Summer and autumn were protective factors for sufficiency, while natural conception was an associated factor for deficiency. CONCLUSION: Severe vitamin D deficiency is widespread. Findings advocate for routine perinatal vitamin D screening and supplementation, with tailored strategies for winter and specific subgroups.