Prevalence and determinants of vitamin D deficiency in pregnant women and their neonates: a multicentric study in Switzerland

Vitamin D deficiency during pregnancy is associated with negative health consequences for the mothers and their neonates. From a public health perspective, evaluating the vitamin D status of pregnant women is therefore crucial, but the data was lacking in Switzerland. Our study aimed to measure the prevalence and to identify the determinants of vitamin D deficiency in a sample of 3 rd-trimester pregnant women in Switzerland. In addition, we evaluated serum 25-hydroxy-vitaminD (25(OH)D) levels in the cord blood of neonates. A three-center cohort study was conducted between August 2014 and June 2016 in the birth clinics of Zurich (latitude 47.4 °, altitude 408 m), Bellinzona (latitude 46.2 °, altitude 238 m) and Samedan (latitude 46.5 °, altitude 1,721 m). We measured serum 25(OH)D in 305 women in their 3 rd trimester of pregnancy and in the cord blood of 278 of their offspring at birth. We used demographic and questionnaire data to explore the determinants of vitamin D deficiency (serum 25(OH)D< 20 ng/mL). Median concentration of serum 25(OH)D in the 3 rd trimester of pregnancy was 18.43 ng/mL (Q1-Q3: 12.2 – 27.4), which translated into a 53.4% prevalence of vitamin D deficiency. Multivariable logistic regression analysis showed that significant determinants of vitamin D deficiency were the center of study (lower risk in Bellinzona), the country of origin (lower risk for Swiss citizens), the season of delivery (lower risk in the summer and fall) and the intake of vitamin D supplements. In the cord blood of the neonates, median serum 25(OH)D level was 20.0 ng/mL (Q1-Q3: 12.4 – 30.7). A strong correlation was observed between serum 25(OH)D of the mothers and their neonates (Spearman“s correlation rho = 0.79, p < 0.0001).

Our study indicates that low vitamin D levels are common in pregnant women living in Switzerland and their neonates. These findings suggest that vitamin D supplementation during pregnancy should receive more attention in clinical practice.