Vitamin D in Pregnancy
Adequate maternal 25-hydroxyvitamin D is important for fetal skeletal development and appears to reduce the risk of several pregnancy complications. Deficiency is common — surveys show 30–60% of pregnant women in temperate countries have serum 25(OH)D below 30 ng/mL.
Recommended intake
The IOM sets the RDA in pregnancy at 600 IU/day (15 µg), the same as non-pregnant adults. The Endocrine Society recommends up to 1,500–2,000 IU/day to maintain serum 25(OH)D at ≥ 40 ng/mL, arguing this level is more appropriate for maternal and fetal health. The upper limit remains 4,000 IU/day.
Deficiency-associated risks
- Preeclampsia: meta-analyses show a 40–50% relative-risk reduction with supplementation, especially when started early.
- Gestational diabetes mellitus (GDM): deficient women have ~1.5× the odds; supplementation modestly reduces incidence.
- Small-for-gestational-age (SGA) births: reduced with supplementation in deficient populations.
- Neonatal hypocalcaemia: severe maternal deficiency can lead to hypocalcaemic seizures in the newborn.
- Craniotabes and congenital rickets: rare but reported in infants of severely deficient mothers.
Testing during pregnancy
Serum 25(OH)D testing is recommended at the first prenatal visit for women with risk factors: darker skin, veiling, obesity, malabsorption, or a history of gestational diabetes. Below 20 ng/mL, most obstetrics guidelines advise 2,000–4,000 IU/day cholecalciferol through pregnancy and lactation. Confirm dosing with your obstetrician.
After birth: mother and baby
Breast milk contains very little vitamin D. All breastfed infants should receive 400 IU/day cholecalciferol from birth (AAP 2008; Health Canada). Alternatively, maternal supplementation with 6,400 IU/day has been shown to raise breast-milk vitamin D to levels sufficient for the infant (Hollis et al. 2015), though this dose exceeds the standard UL and requires physician oversight.