High prevalence of severe vitamin D deficiency during the first trimester in pregnant women in Switzerland and its potential contributions to adverse outcomes in the pregnancy

We performed a retrospective analysis of serum 25(OH)D concentrations in pregnant Swiss women and found a mean serum 25(OH)D level of about 37 nmol/l and that one third of the overall study population had a serum 25(OH)D level below 25 nmol/l, and were thus seriously vitamin D deficient. Furthermore, the data demonstrate that vitamin D deficiency is associated with gestational diabetes. The current recommendations of vitamin D supplementation of 600 IU in pregnant women are therefore insufficient, and novel strategies, such as general screening for vitamin D deficiency, pre-conceptional timing of the supplementation and individually tailored dosing of vitamin D supplementation seem mandatory, potentially leading to improved maternal health and benefits to children’s long-term health in Switzerland and worldwide. (trial registration ClinicalTrial.gov. Identifier: NCT02904720).