Prenatal Vitamins
Summary
Folic acid before and in early pregnancy cut neural tube defects by about 70% in a Cochrane review (grade A), and the USPSTF advises 400–800 mcg/day. Iron lowered anemia at term (grade B). Full multiple-micronutrient formulas reduced low birthweight by 12% versus iron-folic acid in mostly low- and middle-income settings (grade A).
Key facts
- A multivitamin-mineral formula for pregnancy; the core ingredients with trial evidence are folic acid, iron and iodine[1][2][5]
- Neural tube defects down about 70% with folic acid (A); maternal anemia at term down with iron (B); low birthweight down 12% with multiple micronutrients vs iron-folic acid (A)[2][4][5]
- Pregnancy RDA for iodine 220 mcg; iodine UL 1,100 mcg/day for adults[1]
- Iodine: antithyroid drugs; potassium iodide with ACE inhibitors or potassium-sparing diuretics (high potassium)[1]
- Gastrointestinal effects from iron (evidence on rates very uncertain)[5]
- 3 graded human outcomes on this page
- October 10, 2026
How it works
EstablishedFolate is needed to close the neural tube in the first weeks of pregnancy, often before a pregnancy is known. Iron supports the expanded red-cell mass of pregnancy, and iodine is needed for maternal and fetal thyroid hormone, which the fetus depends on early in pregnancy.[1][2][5]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Multiple micronutrients | Grade A | Improved | Systematic review of 18 trials · n = 68,801 · 2019 | 1 row |
| Folic acid | Grade A | Improved | Systematic review of 5 trials · n = 6,708 · 2015 | 1 row |
| Iron | Grade B | Improved | Systematic review of 14 trials · n = 13,543 · 2024 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Low birthweight (multiple micronutrients vs iron-folic acid) | Improved | Grade A | Systematic review · n = 68,801 · 2019 Pregnant women, 18 trials, mostly in low- and middle-income countries Form: multiple-micronutrient supplements with iron and folic acid · Dose: Formulas varied (often the UNIMMAP formula) · Duration: From enrolment in pregnancy to delivery Low birthweight fell 12% (RR 0.88, 95% CI 0.85–0.91; high-quality evidence) and small-for-gestational-age births 8% (RR 0.92). Preterm birth fell slightly (RR 0.95) with a CI crossing no effect; mortality outcomes did not change. | 30873598 (opens PubMed)Source [4] |
| Neural tube defects (folic acid) | Improved | Grade A | Systematic review · n = 6,708 · 2015 Women planning pregnancy or in early pregnancy, in 5 RCTs (births with NTD data) Form: folic acid alone or in a multivitamin · Dose: 400 mcg/day or more · Duration: Around conception and early pregnancy Neural tube defects were less frequent with folic acid (RR 0.31, 95% CI 0.17–0.58; high-quality evidence), and recurrence fell too (RR 0.34). No clear effect on other birth defects. | 26662928 (opens PubMed)Source [2] |
| Maternal anemia and iron deficiency at term (iron) | Improved | Grade B | Systematic review · n = 13,543 · 2024 Pregnant women in 14 RCTs (anemia outcome) Form: daily oral iron · Dose: Daily oral iron (doses varied) · Duration: Pregnancy Anemia at term 4.0% vs 7.4% (RR 0.30; low certainty); iron-deficiency anemia 5.0% vs 18.4% (RR 0.41; moderate certainty). Low birthweight was probably slightly lower (RR 0.84); preterm birth and neonatal death did not clearly differ. | 39145520 (opens PubMed)Source [5] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Prenatal multivitamin tablet or capsule | Varies[1] | Varies by nutrient; potassium iodide is absorbed almost completely (96.4%).[1] | Iron is the ingredient most linked to stomach upset; the evidence on rates is very uncertain.[5] | Folic acid, iron and iodine needs in pregnancy |
| Multiple-micronutrient supplement (e.g. UNIMMAP formula) | Varies[4] | No specific absorption data in our sources.[4] | No important harms found for mortality outcomes.[4] | Birth outcomes vs iron-folic acid in low- and middle-income settings |
| Folic acid alone (400–800 mcg) | Varies[2][3] | No specific absorption data in our sources.[2] | No harms identified in the Cochrane review.[2] | Neural tube defects |
Studied doses
Doses studied in human trials ranged from 400 mcg/day of folic acid upward, with no extra benefit seen above 400 mcg; the USPSTF advises 400–800 mcg/day for anyone who could become pregnant. Iodine at 150 mcg/day is advised by the American Thyroid Association, and iron doses varied across trials.[1][2][3]
Intake reference: Pregnancy RDA for iodine is 220 mcg/day (290 mcg in lactation); the iodine UL is 1,100 mcg/day for adults. The USPSTF advises 400–800 mcg/day of folic acid for anyone who could become pregnant.[1][3] Iodine UL 1,100 mcg/day applies to food plus supplements. NIH ODS fact sheet (updated November 5, 2024).
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Who should be careful
- Check for iodine
- Only 34 of 59 best-selling US prenatal vitamins contained iodine in a 2016–2017 survey, so a label without iodine leaves that gap open.[1]
- Thyroid conditions
- People with autoimmune thyroid disease may react to iodine intakes that are safe for others; high-dose iodine supplements were linked to raised TSH in pregnant women in Spain.[1]
- Iron needs differ
- Iron reduced anemia at term, but evidence on side effects is very uncertain; how much iron is right depends on blood tests and the care team.[5]
- Multiple micronutrient evidence
- The birthweight benefits come mainly from low- and middle-income countries versus iron-folic acid; the single UK placebo trial found no effect on those outcomes.[4]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety
Prenatal vitamins are routine in pregnancy; the main checks are iodine dose, thyroid conditions and iron tolerance.
- Iron side effects
- Adverse effects were 21.6% vs 18.0% with iron vs placebo, but the evidence was very uncertain.[5]
- Iodine excess
- Very high iodine can cause goiter, high TSH and hypothyroidism, the same signs as deficiency.[1]
- No effect on other defects
- Folic acid did not clearly change rates of cleft lip, cleft palate or heart defects.[2]
How to read the label
- Folic acid amountLook for 400–800 mcg of folic acid. Trials found no extra benefit above 400 mcg.[2][3]
- IodineThe American Thyroid Association advises 150 mcg/day of iodine as potassium iodide before, during and after pregnancy. Surveyed prenatals that had iodine contained 25–290 mcg (median 150 mcg).[1]
- Stay under the iodine ULIodine-only supplements sometimes exceed the 1,100 mcg/day UL; prenatals usually do not.[1]
Cost per studied dose, without the sales pitch
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Cost per studied dose
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Frequently asked questions
Why does folic acid matter so much?
In a Cochrane review of 5 trials, folic acid around conception cut neural tube defects by about 70% (RR 0.31). The USPSTF gives folic acid 400–800 mcg/day an A recommendation for anyone who could become pregnant.[2][3]
When should prenatal vitamins start?
The folic acid evidence is periconceptional: the USPSTF advice covers anyone planning or able to become pregnant, because the neural tube forms very early.[2][3]
Do prenatal vitamins need iodine?
The American Thyroid Association advises 150 mcg/day, yet only 34 of 59 best-selling US prenatals contained iodine in one survey.[1]
Is more folic acid better?
No extra benefit was seen above 400 mcg/day in the Cochrane analysis; the USPSTF range tops out at 800 mcg.[2][3]
Does iron in prenatal vitamins help?
Daily iron lowered anemia at term (4.0% vs 7.4%) and iron-deficiency anemia, with little or no difference in preterm birth.[5]
Do full multivitamins beat iron-folic acid?
In mostly low- and middle-income settings, yes for low birthweight (12% fewer) and small-for-gestational-age births, with no change in mortality.[4]
Sources
- [1]Iodine: Fact Sheet for Health Professionals (updated November 5, 2024). NIH Office of Dietary Supplements, 2024. fact-sheet
- [2]Effects and safety of periconceptional oral folate supplementation for preventing birth defects.. Cochrane Database Syst Rev, 2015. systematic-review
- [3]Folic Acid Supplementation to Prevent Neural Tube Defects: US Preventive Services Task Force Reaffirmation Recommendation Statement.. JAMA, 2023. guideline
- [4]Multiple-micronutrient supplementation for women during pregnancy.. Cochrane Database Syst Rev, 2019. systematic-review
- [5]Daily oral iron supplementation during pregnancy.. Cochrane Database Syst Rev, 2024. systematic-review
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every figure re-checked against the Cochrane abstracts (folic acid 2015, MMS 2019, iron 2024), the USPSTF 2023 statement and the ODS iodine fact sheet; setting caveat (low- and middle-income countries, iron-folic acid comparator) added to the MMS row. Page set indexable.