AbstractThe prevalence of vitamin D deficiency in pregnant white‐skinned women (WSW) and their infants has not been investigated at northern latitudes in a developed county. A 2‐year observational cohort study was undertaken in the North West of England to determine 25‐hydroxyvitamin D (25OHD) levels in WSW and their infants during pregnancy and 4 months postdelivery and to explore factors associated with these levels. Nutritional and lifestyle questionnaires were completed and 25OHD levels measured at 28 weeks and 4 months postdelivery.Twenty‐seven percent and 7% of WSW had insufficient and deficient levels of 25OHD during pregnancy and 48% and 11% four months postdelivery. WSW with Fitzpatrick skin‐type I (FST I) have significantly lower 25OHD than other skin types after controlling for time spent outside and vitamin D intake. Twenty‐four percent and 13% of infants had insufficient and deficient 25OHD levels at 4 months. Unsupplemented breast‐fed infants have the highest level of insufficiency (67%) compared with formula‐fed infants (2%). Factors associated with infant serum 25OHD levels at 4 months included breast feeding, supplementation, and time outside. WSW have a high prevalence of insufficiency and deficiency during pregnancy which doubles 4 months after birth. Breast‐fed infants of WSW are rarely considered at risk of vitamin D insufficiency but have high rates compared with formula‐fed infants. This is the first study to show the finding that FST I WSW have significantly lower levels of 25OHD than those with FST II–IV (difference adjusted for diet and time outside 14 (95%CI 7–21) nmol/L).