Folate for Pregnancy
For preventing fetal neural tube defects, taking folic acid before and during early pregnancy is one of the best-proven interventions in all of nutrition: it cuts the risk by roughly two-thirds. The catch is timing — it only works if started about a month before conception.
Why this grade7-layer evidence engine
This earns the top "Strong Evidence" tier because the causal case is exceptionally solid. Two landmark double-blind randomized trials anchor it: the MRC Vitamin Study (PMID 1677062, 1,817 high-risk women) found a 72% drop in neural tube defect recurrence (RR 0.28), and Czeizel and Dudas (PMID 1307234, 7,540 women) recorded zero defect cases on folic-acid-containing vitamins versus six in controls.
A high-quality 2015 Cochrane review (PMID 26662928; 5 trials, 7,391 women) confirmed a more-than-two-thirds reduction in defect-affected pregnancies (RR 0.31, 95% CI 0.17-0.58), and a 2023 USPSTF evidence report (PMID 37526714; observational, ~1.2 million people) re-confirmed it (adjusted RR ~0.49-0.62). Regulators are unanimous: the US FDA authorizes a neural-tube-defect health claim and mandates grain fortification, while the UK NHS and WHO recommend 400 micrograms daily for anyone who could become pregnant.
Two caveats explain the "published with warning" status. Timing is decisive — the neural tube closes by about 28 days, so supplementation must begin roughly a month before conception, and the benefit is specific to neural tube defects, not other birth defects. The Mayo Clinic advises starting at least one month before trying to conceive and continuing through week 12. High-dose folic acid can also mask vitamin B12 deficiency, which is why an adult upper limit of 1,000 micrograms per day applies.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.79
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (2 篇 > 0 negative)
- tier_strict_requirement_check — A 級條件達標
- detect_disputes — 偵測到 0 個 hard + 1 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status