The aim of the present study was to examine the prevalence and associated factors of dietary supplement use, particularly supplements containing vitamin D and fatty acids, in pregnant women enrolled in a multi-national study.

The Environmental Determinants of Diabetes in the Young (TEDDY) study is a prospective longitudinal cohort study. Maternal dietary supplement use was self-reported through questionnaires at month 3 to 4 postpartum.

Six clinical research centres; three in the USA (Colorado, Georgia/Florida and Washington) and three in Europe (Sweden, Finland and Germany).

Mothers (n 7326) to infants screened for high-risk HLA-DQ genotypes of type 1 diabetes.

Ninety-two per cent of the 7326 women used one or more types of supplement during pregnancy. Vitamin D supplements were taken by 65% of the women, with the highest proportion of users in the USA (80?5 %). Overall, 16% of the women reported taking fatty acid supplements and a growing trend was seen in all countries between 2004 and 2010 (P,0?0001). The use was more common in Germany (32 %) and the USA (24 %) compared with Finland (8?5%) and Sweden (7?0 %). Being pregnant with the first child was a strong predictor for any supplement use in all countries. Low maternal age (,25 years), higher education, BMI$25?0 kg/m2 and smoking during pregnancy were factors associated with supplement use in some but not all countries.

The majority of the women used dietary supplements during pregnancy. The use was associated with sociodemographic and behavioural factors, such as parity, maternal age, education, BMI and maternal smoking.