Methods: Healthy pregnant women between 18-42 years of age without history of pregnancy complications will be recruited for a double-blind, randomized, controlled trial where they will receive one of three different dosages of vitamin D (10, 25 and 50ug/day) as part of a standard prenatal vitamin. The study at 18 plus/minus 3 weeks gestation and will carry on throughout pregnancy and lactation. Mother and infant vitamin D levels in breast milk and blood will be measured at regular intervals. Skin colour will be measured via light reflectometry. Bone biomarkers such as plasma osteocalcin and urinary n-telopeptide will be assessed. Dietary vitamin D intake and sun exposure will be estimated using a food frequency and lifestyle questionnaire. Data will be analyzed using multiple regression analysis controlling for baseline values.