Recommended Preconception Vitamin D Dose
Women planning pregnancy should supplement with at least 1,000 IU (40 mcg) of vitamin D daily, starting 2-3 months before planned conception, to maintain serum 25-hydroxyvitamin D levels above 50 nmol/L (20 ng/mL). 1
Core Dosing Recommendation
The minimum effective dose is 1,000 IU daily as recommended by the American College of Obstetricians and Gynecologists, with the target of achieving serum 25-hydroxyvitamin D ≥50 nmol/L (20 ng/mL) and maintaining parathyroid hormone (PTH) within normal limits. 1
Use vitamin D₃ (cholecalciferol) rather than D₂ (ergocalciferol), as D₃ is more effective at raising and maintaining serum levels. 1
Begin supplementation 2-3 months before planned conception to optimize vitamin D stores prior to pregnancy, as recommended by the Endocrine Society. 1
Important Evidence Considerations
While the guideline recommends 1,000 IU daily as the minimum dose, recent research suggests this may be insufficient for many women:
A 2024 prospective cohort study found that 1,000 IU daily had limited effectiveness, with 67% of vitamin D-deficient participants remaining deficient after 16 weeks of supplementation. 2
A 2014 randomized controlled trial demonstrated that 2,000 IU daily achieved vitamin D sufficiency in 80% of pregnant women, compared to only 42% with 600 IU and 39% with 1,200 IU daily. 3
A 2018 prospective cohort study showed that preconception vitamin D sufficiency (≥75 nmol/L) was associated with increased likelihood of livebirth (RR 1.15) and reduced pregnancy loss (RR 0.88 per 25 nmol/L increase). 4
Given this evidence, consider starting with 2,000 IU daily for women at higher risk of deficiency, particularly if baseline levels are unknown.
Monitoring Strategy
Check baseline serum 25-hydroxyvitamin D levels along with calcium, phosphate, magnesium, and PTH before starting supplementation, especially in high-risk women. 1
Recheck levels every 6 months during the preconception period to ensure adequate supplementation. 1
Reassess 3-6 months after any dose adjustment to verify therapeutic response. 1
Add calcium supplementation (1,200-1,500 mg daily in divided doses) if needed to maintain PTH within normal limits. 1
High-Risk Populations Requiring Special Attention
Women with BMI >30 kg/m² require the same vitamin D dose (at least 1,000 IU daily) but should also receive higher folic acid (4-5 mg daily vs. 0.4 mg). 1
Women with history of bariatric surgery require more intensive monitoring (every 6 months) and individualized dose adjustment based on serum levels. 1
Women with limited sun exposure, darker skin pigmentation, or malabsorption disorders should have baseline levels checked and supplementation adjusted accordingly, as they are at higher risk of deficiency. 1
Integration with Comprehensive Preconception Care
Combine vitamin D with prenatal vitamins containing at least 400 mcg folic acid (or 4-5 mg for women with BMI >30 or diabetes), recognizing that standard prenatal vitamins typically contain only 400 IU of vitamin D. 1
Add potassium iodide (150 mcg daily) for thyroid function support as part of comprehensive preconception supplementation. 1
Critical Pitfalls to Avoid
Do not delay supplementation until pregnancy confirmation, as early pregnancy is a critical period for vitamin D-dependent processes and neural tube development. 1
Do not supplement without baseline assessment in high-risk women, as individual requirements vary significantly and some may need higher doses. 1
Do not assume 1,000 IU is adequate for all women—recent evidence suggests many women, particularly those with baseline deficiency, may require 2,000 IU or higher to achieve sufficiency. 3, 2
Separate calcium supplements from iron supplements by at least 2 hours, as they interfere with each other's absorption. 5