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

BackgroundLarge-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.MethodsThis retrospective cohort included 20,693 early-pregnant women (