Effects of Age, Season, and Pregnancy History on Vitamin D Status in Women Seeking Preconception Care

BACKGROUND Vitamin D is crucial for overall health. While prenatal deficiency is linked to poor obstetric outcomes, its preconception levels are less studied. This investigation sought to characterize the distribution and influencing factors of serum 25-hydroxyvitamin D levels among women undergoing preconception care. MATERIAL AND METHODS This cross-sectional, retrospective study included a total of 1050 women who received preconception consultations between January and December 2023. Clinical parameters such as age, serum 25(OH)D level, testing period, and pregnancy history were analyzed. RESULTS The median serum 25(OH)D level was 17.97 (14.47, 21.84) ng/ml. Vitamin D deficiency (<20 ng/mL) was identified in 63.07% of participants. An age-related elevation in serum 25(OH)D was observed (ß=0.116, 95% CI: 0.073-0.246, P<0.001), accompanied by a corresponding decline in deficiency prevalence (OR=0.945, 95% CI: 0.913-0.978, P=0.001). Women with any pregnancy history had higher serum 25(OH)D levels (ß=0.156, 95% CI: 0.874-2.671, P<0.001) and lower vitamin D deficiency (OR=1.717, 95% CI: 1.209-2.439, P=0.003) than those without. Concentrations measured during summer and autumn were markedly greater versus those recorded in winter and spring (P<0.05). Mixed-effects linear regression analysis and multivariable logistic regression analysis indicated that serum 25(OH)D levels and vitamin D deficiency were markedly modulated by age, pregnancy history, and seasonal variation. CONCLUSIONS Vitamin D deficiency was common among women receiving preconception care. Serum vitamin D levels were associated with age, season, and pregnancy history.