Table 1 Characteristics of the randomized controlled trials

Goldring, 2013 [26]

Single-center non-blinded

non-placebo

RCT

Pregnant women in London (51°N) (27 weeks gestation, Asian, Middle Eastern, Black and White) without sarcoidosis, osteomalacia, renal dysfunction or tuberculosis

1. Daily vitamin D (800 IU ergocalciferol until delivery) (n = 60)

2. Bolus vitamin D (a single oral dose of 200,000 IU cholecalciferol (n = 60)

No treatment (n = 60)

1.Wheeze ever (ISAAC, at age 3)

2. Recurrent wheezing (≥2 episodes of reported wheezing since birth, at age 3)

3. Wheeze in the year prior to assessment (ISAAC, at age 3)

4. Wheeze with a positive asthma predictive index (loose criteria, at age 3)

Chawes, 2016 [27]

Single-center double-blinded RCT

Pregnant women in Denmark (55°43’N) (≤26 gestational week) without any endocrine, cardiovascular, or nephrological disorders; or vitamin D3 (cholecalciferol) intake more than 600 IU/d

Daily dose of 2400 IU vitamin D3 supplementation (24 gestational week to 1 week postpartum) (n = 315)

Matching placebo tablets (Camette A/S) (24 gestational week to 1 week postpartum) (n = 308)

1.Persistent wheeze (diagnosed according to a previously validated quantitative algorithm, from birth to age 3 years)

2.Asthma (doctor diagnosed in children fulfilling the persistent wheeze criteria at age 3)

Litonjua, 2016 [28]

Multicenterdouble-blinded placebo RCT

Pregnant women in Boston (52°58’N), Washington (38°53’N), San Diego (32°43’ N) (age 18–39,10–18 gestational week, nonsmoker, English or Spanish speaking, who or whose partner had a history of allergic disease, with intent to participate for 4 years)

Daily 4000 IU of vitamin D plus a multivitamin with 400 IU of vitamin D (n = 440)

Placebo (daily placebo pill plus a multivitamin with 400 IU of vitamin D) (n = 436)

Asthma or recurrent wheeze in first 3 y of life (parental report, every 3 months)