Vitamin D status and its determinants in healthy pregnant women living in Switzerland in the first trimester of pregnancy

The effect of vitamin D deficiency has been associated with adverse outcomes both on maternal health and foetal development. Many country-specific studies have shown that vitamin D deficiency is a common problem in reproductive-aged women, yet no data is available for pregnant women living in Switzerland. Our study aimed at assessing the level of deficiency (25(OH)D< 20 ng/mL) and identifying the determinants of low circulating vitamin D levels in pregnant women. From September 2014 through December 2015, 204 pregnant women were conveniently recruited during their first clinical appointment (between week 6 and 12 of pregnancy) at the Clinic of Obstetrics of the University Hospital Zurich. Blood samples were collected and a questionnaire focusing on lifestyle and skin colour was completed face to face with the responsible physician. Logistic regression analyses were performed with vitamin D status (deficient versus sufficient) as dependent variable. Median vitamin D concentration in the overall sample was 17.1 ng/mL [Q1, Q3: 9.78, 22.3] with 63.2% of participating women being vitamin-D deficient.

The highest proportions of vitamin D deficiency were detected in women originating from South East Asia Pacific (88.5% of deficiency, median vitamin D level of 8.4 ng/mL [Q1, Q3: 6.10, 14.88]) and from Africa and Middle East (91.4% of deficiency, median vitamin D level of 10.7 ng/mL [Q1, Q3: 6.55, 14.45]). Multivariable logistic regression showed that risk factors of vitamin D deficiency are country of origin (women born in Switzerland and Germany had a lower risk than women born in other countries), smoking status (lower risk for former smokers) and intake of vitamin D supplements. Our results confirm a high prevalence of vitamin D deficiency in this Swiss cohort, in particular in women coming from Asian and African countries, and underline the importance of appropriate counselling and vitamin D supplementation in early pregnancy.