Randomized Trial: Maternal Vitamin D Supplementation to Prevent Childhood Asthma (VDAART)

Inclusion Criteria: * Personal history of asthma, eczema, allergic rhinitis or a history of asthma, eczema, allergic rhinitis in the biological father of the child * Gestational age between 10 and 18 weeks at the time of randomization * Maternal age between 18 and 39 years * Not a current smoker * English or Spanish speaking * Intent to participate for the full 4 years (through Pregnancy and then until the 3rd birthday of the child) Exclusion Criteria: * Not meeting inclusion criteria * Gestational age greater than 18 weeks * Presence of chronic medical conditions * Taking vitamin D supplements containing more than 2000 IU/day of vitamin D3 * Multiple gestation pregnancy (twins, triplets) * Pregnancy achieved by assisted reproduction techniques (e.g., IUI, IVF)