VDAART design (clinicaltrials.gov Identifier: {"type":"clinical-trial","attrs":{"text":"NCT00920621","term_id":"NCT00920621"}}NCT00920621)

Pregnant women were recruited from 3 clinical sites across the United States: (1) Boston Medical Center, Boston, MA; (2) Washington University at St. Louis, St. Louis, MO; and (3) Kaiser Permanente Southern California Region, San Diego, CA, as previously detailed[7]. Eligible participants were pregnant non-smoking women aged 18 to 39 years in estimated gestational age 10 to 18 weeks, who had a history of asthma, eczema, or allergic rhinitis or conceived the child with a man with a history of such diseases[7,9], excluding women with other chronic disorders.

The families were followed by telephone interviews every 3 months, capturing diagnoses, symptoms and the medication use of the child. In addition, the mother and child attended the clinics for yearly follow-up visits at age 1, 2 and 3 years. Content of VDAART prenatal and postnatal visits is previously reported[7].

The women were randomized 1:1, between 10–18 weeks of gestation, to a daily intake of 4,000 IU vitamin D₃ plus a multivitamin containing 400 IU vitamin D₃ or a matching placebo tablet plus a multivitamin containing 400 IU vitamin D₃, i.e. 4,400 vs. 400 IU vitamin D₃ supplement per day. The intervention was continued until delivery. Adherence was measured by MEMS^® (Medication Events Monitoring Systems) caps, an electronic cap that recorded each time the tablet container was opened[7].

Blood was drawn from the mothers at entry to the trial and at the 3^rd trimester visit (32 to 38 weeks of gestation) for measurement of circulating levels of 25(OH)D, determined by using the DiaSorin Liaison® chemiluminescence immunoassay[13].