Vitamin D During Pregnancy and Infancy and Infant Serum 25-Hydroxyvitamin D Concentration

Randomized, double-blind trial in Auckland, New Zealand, enrolling pregnant women with singleton pregnancies at 26 to 30 weeks' gestation from a community-based primary care maternity clinic and following their healthy infants to 6 months. The active vitamin D3 arms included 87 participants in the lower-dose group and 86 participants in the higher-dose group in a 1:1:1 design that also included placebo.

Oral vitamin D3 drops were given from 26 to 30 weeks' gestation until delivery for mothers and from birth to 6 months for infants. The lower-dose regimen used 1000 IU/day for mothers and 400 IU/day for infants; the higher-dose regimen used 2000 IU/day for mothers and 800 IU/day for infants.

Vitamin D3 supplementation increased maternal and infant serum 25(OH)D concentrations versus placebo, with the higher-dose arm generally achieving the highest values across time points. Maternal median 25(OH)D at 36 weeks was 39 and 41 ng/mL in the lower- and higher-dose arms versus 20 ng/mL with placebo; cord blood medians were 24 and 26 versus 13 ng/mL; and infant medians at 2 months were 34 and 43 versus 20 ng/mL. At 6 months, infant medians were 34 and 38 ng/mL versus 31 ng/mL, while the proportion reaching 25(OH)D ≥20 ng/mL was 82% and 89% versus 74%, and the proportion reaching ≥30 ng/mL was 74% and 73% versus 57%.

The trial was modest in size and followed infants only to 6 months, so longer-term durability and clinical outcomes were not assessed. Hypercalcemia was monitored, but specific event counts were not reported. Arm-specific ethnicity, dietary intake, physical activity, and BMI distributions were not provided, and the single-city New Zealand setting may limit generalizability; some additional vitamin D supplement use occurred during the study, although it was reportedly balanced across arms.