Suboptimal maternal vitamin D status and low education level as determinants of small-for-gestational-age birth weight.

PURPOSE This study aimed firstly to investigate the contribution of maternal 25(OH) vitamin D to the association of maternal education and small-for-gestational-age birth weight (SGA) and secondly to examine whether the contribution of 25(OH) vitamin D differs by overweight, season, and maternal smoking. METHODS Logistic regression analysis was carried out in this study, using data of 2,274 pregnant women of Dutch ethnicity from the ABCD study, a population-based cohort study in the Netherlands. Maternal 25(OH) vitamin D was measured in early pregnancy. Stratified analyses were conducted for overweight, season of blood sampling, and smoking. RESULTS Low-educated women had lower 25(OH) vitamin D levels compared to high-educated women, and women in the lowest 25(OH) vitamin D quartile had a higher risk of SGA offspring. In addition, low-educated women had a higher risk of SGA offspring (OR 1.95 [95% CI: 1.20-3.14]). This association decreased with 7% after adjustment for 25(OH) vitamin D (OR 1.88 [95% CI 1.16-3.04]). In stratified analyses, adjustment for 25(OH) vitamin D resulted in a decrease in OR of about 17% in overweight women and about 15% in women who conceived in wintertime. CONCLUSIONS 25(OH) vitamin D appears to be a modifiable contributor to the association between low maternal education and SGA offspring, particularly in overweight women and women who conceived in the winter period. In those women, increasing the intake of vitamin D, either through dietary adaptation or through supplementation in order to achieve the recommendation, could be beneficial.