Vitamin B-12 supplementation during pregnancy and early lactation increases maternal, breast milk, and infant measures of vitamin B-12 status.

Randomized, double-blind, placebo-controlled trial in pregnant women aged at least 18 years in urban Bangalore, India. Participants were enrolled before or at 14 weeks of gestation and followed through 6 weeks postpartum; the population was described as women from lower socioeconomic backgrounds.

Oral vitamin B-12 50 mg daily from enrollment through 6 weeks postpartum, compared with placebo. Supplementation began before or at 14 weeks of gestation and continued into early lactation.

Vitamin B-12 supplementation improved maternal, breast milk, and infant vitamin B-12 status, but it did not clearly improve birth outcomes. In the vitamin B-12 group, median maternal plasma B-12 was higher than placebo in the second trimester (216 vs 112 pmol/L, P < 0.001) and third trimester (184 vs 105 pmol/L, P < 0.001), and breast milk B-12 at 6 weeks postpartum was higher (136 vs 87 pmol/L, P < 0.0005). Infant status also improved at 6 weeks, with higher plasma B-12 (199 vs 139 pmol/L, P < 0.001) and lower MMA (0.09 vs 0.16 mmol/L, P = 0.022) and homocysteine (10.9 vs 21.0 mmol/L, P < 0.001). Birth weight, low birth weight, and IUGR were not significantly different between groups.

Biochemical follow-up sample sizes were smaller than the randomized cohort, especially for infant and breast milk measures, which may limit precision. Breast milk vitamin B-12 at 3 and 6 months postpartum was not significantly different between groups, and clinical birth outcomes were not improved, suggesting limited power for harder endpoints. Generalizability is limited to urban south Indian pregnant women with substantial baseline vitamin B-12 deficiency risk.