Vitamin D Supplementation in Pregnant Women
All pregnant women should take at least 1,000 IU (40 mcg) of vitamin D daily throughout pregnancy, with a target serum 25-hydroxyvitamin D level of ≥50 nmol/L (20 ng/mL), as this dose is necessary to prevent adverse maternal and fetal outcomes. 1, 2
Standard Supplementation Protocol
- The minimum effective dose is 1,000 IU (40 mcg) daily, not the commonly cited 600 IU, which is insufficient for pregnancy requirements 2
- Use vitamin D₃ (cholecalciferol) rather than D₂ (ergocalciferol), as D₃ is more effective at raising and maintaining serum levels 1
- Begin supplementation at least 2-3 months before planned conception to optimize vitamin D stores 1
- Continue supplementation throughout pregnancy and into the postpartum period, especially during breastfeeding 3
Monitoring Requirements
Baseline assessment should include:
- Serum 25-hydroxyvitamin D levels before conception or early in pregnancy 2
- Concurrent measurement of calcium, phosphate, magnesium, and parathyroid hormone (PTH) 2
During pregnancy:
- Monitor at least once per trimester using pregnancy-specific reference ranges 2
- Recheck 3-6 months after any dose adjustment 1
- Target serum level: ≥50 nmol/L (20 ng/mL) with PTH maintained within normal limits 1, 2
Special Populations Requiring Attention
Women with obesity (BMI >30 kg/m²):
- Require the same vitamin D dose (minimum 1,000 IU daily) 2
- Must also receive higher folic acid supplementation: 4-5 mg daily versus standard 0.4 mg 2
Women with history of bariatric surgery:
- Require minimum 1,000 IU (40 mcg) daily with more intensive monitoring 2
- Should undergo nutritional screening during each trimester including vitamin D, calcium, ferritin, folate, vitamin B12, and vitamin A 4
- Need specialist antenatal care and more frequent review with bariatric dietitian 4
- Reference ranges change in pregnancy; use perinatal-specific ranges 4
High-risk women requiring baseline assessment:
- Limited sun exposure 1
- Darker skin pigmentation 1
- Malabsorption disorders 1
- Women with cystic fibrosis (require additional 600 IU daily on top of baseline) 2
Clinical Rationale: Why This Matters
Vitamin D deficiency (affecting 46-83% of pregnant women) is associated with:
- Preeclampsia (reduced risk with levels ≥30 ng/mL in third trimester: OR 0.34) 5
- Preterm birth 6, 7
- Small-for-gestational-age infants and low birth weight 6, 7
- Spontaneous abortion 6, 7
- Gestational diabetes mellitus 6
- Neonatal hypocalcemia and poor postnatal growth 8
Supplementation >400 IU/day reduces risks of:
- Maternal preeclampsia and miscarriage 6
- Fetal or neonatal mortality 6
- Vitamin D deficiency in offspring 6
- Childhood attention-deficit hyperactivity disorder and autism spectrum disorder 6
- In women with gestational diabetes: hyperbilirubinemia, polyhydramnios, macrosomia, fetal distress, and neonatal hospitalization 6
Critical Pitfalls to Avoid
- Do not rely on 600 IU daily as adequate supplementation, as recent evidence shows it is insufficient for many pregnant women, particularly those at high risk 2
- Do not delay supplementation until pregnancy confirmation, as early pregnancy is a critical period for vitamin D-dependent processes 1
- Do not assume dietary intake is sufficient, as vitamin D from food sources typically does not meet pregnancy requirements 2
- Do not supplement without baseline assessment in high-risk women, as individual requirements vary significantly 1
- Do not use vitamin A in retinol form during pregnancy; only beta-carotene form should be used to avoid toxicity risk 4, 3
- Do not discontinue supplementation postpartum, as nutritional demands remain elevated, especially during breastfeeding (continue ≥1,000 IU daily) 3
Additional Supplementation Considerations
Concurrent supplementation during pregnancy should include: