Vitamin D and Recurrent Miscarriage
Recurrent pregnancy loss (RPL, ≥ 2 clinical losses) affects ~1-2% of women trying to conceive. Vitamin D deficiency is more common in RPL cohorts than in controls, and immune-tolerance mechanisms at the maternal-fetal interface provide biological plausibility. Correcting deficiency is standard part of RPL workup though causal evidence is limited.
Observational data
Meta-analyses find women with recurrent miscarriage have significantly lower mean 25(OH)D than controls. Autoantibody-positive RPL patients (antiphospholipid syndrome, thyroid antibodies) tend to have particularly low levels. Rate of deficiency in RPL cohorts ranges 45-75% in various studies.
Mechanisms
- Vitamin D promotes Treg cells and dampens Th1/Th17 responses — important for maternal immune tolerance of the semi-allogeneic fetus.
- Regulates decidual NK cell function.
- Modulates HOXA10 and endometrial receptivity genes.
- Affects thrombotic and complement pathways relevant to placental function.
Supplementation trials
Small RCTs (Ota 2014 and others) suggest reduced miscarriage rates with vitamin D correction in the deficient. Larger trials are lacking. RCOG and ASRM guidelines mention vitamin D as part of the RPL workup without formal recommendation for supplementation as treatment.
Full RPL workup context
- Antiphospholipid antibodies (lupus anticoagulant, anticardiolipin, anti-β2-GPI).
- Uterine anatomy (saline sonogram, hysteroscopy).
- Karyotyping of both partners; products of conception if available.
- Thyroid function and thyroid antibodies.
- Diabetes screening.
- Vitamin D level.
- Hereditary thrombophilia panel (situation-dependent).
Practical guide
- RPL workup should include 25(OH)D testing.
- Correct deficiency to ≥ 30 ng/mL (some centres target 40+) with 2,000-4,000 IU/day cholecalciferol pre-conception.
- Vitamin D correction complements — not replaces — antiphospholipid syndrome treatment (aspirin + heparin), thyroid management, and other RPL-specific therapy.
- See our pregnancy page for ongoing dosing.