Most prenatal vitamin advice falls into one of two categories: vague reassurance ("just take one daily and you'll be fine") or anxiety-inducing supplement stacking from brands trying to sell you six separate capsules. Neither is useful. What follows is what the clinical evidence actually supports — nutrient by nutrient, with the specific numbers your provider would reference, drawn from the major guidelines bodies and the most recent systematic reviews.
The nutrients with the strongest evidence
Three nutrients have unambiguous, large-scale clinical evidence supporting supplementation during pregnancy. These are not debatable.
Folic acid is the single most evidence-backed prenatal supplement. It reduces neural tube defects — birth defects of the brain and spine, including spina bifida — by more than 70%.1 ACOG recommends 600 micrograms daily during pregnancy, with at least 400 micrograms coming from a supplement, ideally starting one month before conception.2 WHO recommends 400 micrograms daily.3 NICE updated its folic acid guidance in January 2025 (NG247), recommending 400 micrograms for average-risk women and 4–5 milligrams for those with a prior pregnancy affected by NTDs, diabetes, or anticonvulsant use.4
One important distinction: folic acid is the synthetic form that has been specifically researched and proven to prevent NTDs. While "folate" supplements (including 5-MTHF) are widely marketed, ACOG notes that folic acid is the only form with this proven track record.2
A 2025 systematic review raised a nuanced concern: very high-dose folic acid supplementation combined with vitamin B12 deficiency may influence glucose metabolism, though the findings are conflicting and do not change standard recommendations.5
Iron is needed because blood volume increases by roughly 50% during pregnancy. ACOG recommends 27 milligrams daily, up from 18 milligrams when not pregnant.2 WHO recommends 30–60 milligrams of elemental iron daily.3 The evidence from Cochrane-level data shows iron supplementation reduces maternal iron deficiency anaemia at term by 59% and all-cause maternal anaemia by approximately 70%.6
A practical note: if you take gummy prenatal vitamins, they typically contain little to no iron. ACOG advises discussing additional iron supplementation with your provider if you use gummies.2
Iodine is critical for thyroid function and fetal neurodevelopment. The recommended intake increases to 220 micrograms daily during pregnancy.7 Multiple professional organisations recommend 150 micrograms from a supplement for women before and during pregnancy. Not all prenatal vitamins contain iodine — check your label.
The nutrients with strong but evolving evidence
Two nutrients have compelling evidence that continues to strengthen, though guidelines vary more between countries.
Omega-3 fatty acids (DHA) received a significant evidence boost from a landmark 2018 Cochrane Review of 70 randomised controlled trials involving nearly 20,000 women. The findings: omega-3 supplementation reduced the risk of preterm birth by 11% and early preterm birth (before 34 weeks) by 42%.8 In 2024, the European Board and College of Obstetrics and Gynaecology (EBCOG) published a formal position statement establishing clinical practice guidelines based on this evidence.9 The NIH Office of Dietary Supplements updated its guidance in 2025 to state that experts recommend at least 250 milligrams daily of DHA plus EPA, with an additional 100–200 milligrams of DHA during pregnancy.10
Australia's 2021 pregnancy care guidelines went further, recommending 800 milligrams of DHA plus 100 milligrams of EPA daily for women with low omega-3 levels — the most specific dosing guidance of any national body.11
Vitamin D supplementation during pregnancy shows increasingly strong evidence for reducing pregnancy complications. A December 2025 meta-analysis of 24 studies involving 52,372 participants found that vitamin D supplementation reduced preeclampsia risk by 42% and gestational diabetes risk by 45%.12 However, guidelines remain inconsistent: ACOG recommends 600 IU daily, while some researchers argue this is insufficient. Women with darker skin, limited sun exposure, or those living at higher latitudes are at greater risk of deficiency and may need higher doses — discuss testing with your provider.
The nutrient most prenatal vitamins are missing
Choline is arguably the most significant gap in prenatal supplementation. The recommended intake is 450 milligrams daily during pregnancy.7 Over 90% of prenatal vitamins contain little to no choline, or only token amounts under 100 milligrams.13 Most pregnant women have intakes well below recommendations.
A 2025 systematic review of randomised controlled trials and observational studies (Gould et al.) found that while animal studies strongly suggest choline supplementation improves cognitive outcomes in offspring, the human evidence is not yet definitive — the authors concluded that "current evidence is insufficient to support or refute the hypothesis" but noted the trials were small and more research is needed.14 A 2026 review in Ginekologia Polska synthesising current recommendations noted that EFSA suggests 400–480 milligrams daily for pregnant women.15
The practical implication: dietary choline sources (particularly eggs, meat, and fish) are important regardless of supplementation. If your prenatal does not contain at least 200–400 milligrams of choline, consider either a separate choline supplement or deliberate dietary intake.
What the evidence does not support
High-dose antioxidant combinations (vitamins C plus E) are not recommended during pregnancy. A 2025 evidence summary reviewing guidelines from 2020–2025 (covering WHO, ACOG, and NICE) concluded that these combinations lack efficacy and may cause potential harm.6
Taking more than the recommended amount of your prenatal vitamin is also not advised. Some nutrients, particularly vitamin A, can cause birth defects at higher doses. ACOG is explicit: do not take extra prenatal vitamins to compensate for a missed dose.2
What this means for you
The evidence points to a clear hierarchy. Folic acid and iron are non-negotiable — every major guidelines body worldwide recommends both.16 Omega-3 DHA has reached the threshold of clinical practice guidelines for preterm birth prevention. Vitamin D shows strong promise, particularly for those at risk of deficiency. Choline is critically under-supplied in most prenatals and deserves attention through diet or supplementation. And iodine needs to be on the label — not all prenatals include it.
Check your prenatal vitamin against these specific numbers. If it falls short on any of the core nutrients, the conversation with your provider is straightforward: here is what the evidence supports, here is what my supplement contains, what should I add?
