Evidence explainerFertility & Prenatal
Prenatal Vitamins: What the Evidence Says About Folic Acid vs Methylfolate, Choline, DHA and Iodine
Folic acid, started before pregnancy, is the prenatal ingredient with the strongest evidence. Choline and iodine are the nutrients prenatals most often skimp on, and omega-3s modestly cut early preterm birth.
Key takeaways
- The US Preventive Services Task Force recommends that everyone planning or able to become pregnant take 0.4 to 0.8 mg (400 to 800 mcg) of folic acid daily, its top A grade [1].
- The CDC says folic acid is the only form of folate shown to prevent neural tube defects, and that people with an MTHFR gene variant can process it [3][4].
- About 90% to 95% of pregnant women get less than the 450 mg a day of choline recommended, and prenatal supplements typically contain little if any [5].
- A Cochrane review of 70 trials found omega-3 supplements in pregnancy lowered preterm birth before 37 weeks (11.9% vs 13.4%) and before 34 weeks (2.7% vs 4.6%) [7].
- The American Thyroid Association recommends 150 mcg of iodine a day as potassium iodide when planning a pregnancy, pregnant or breastfeeding [8], yet about a quarter of prenatal doses sold in one US analysis had none [9].
Folic acid: start before you try
Neural tube defects form in the first weeks of pregnancy, often before a pregnancy is known, so the CDC advises starting 400 mcg of folic acid at least 1 month before conception [3]. In the landmark Medical Research Council trial, folic acid prevented 72% of repeat neural tube defects in women who had had an affected pregnancy [2].
The USPSTF reaffirmed in 2023, with high certainty of substantial net benefit, that everyone planning or able to become pregnant should take 400 to 800 mcg daily [1]. If you have had a pregnancy affected by a neural tube defect, the CDC says the usual advice is 4,000 mcg a day from 1 month before pregnancy through the first 3 months, after talking with your doctor [3].
Folic acid vs methylfolate (and MTHFR)
Some prenatals use methylfolate (5-MTHF) instead of folic acid, and you may hear that people with MTHFR gene variants should avoid folic acid. The CDC says that advice is not true: people with these variants can process all types of folate, and folic acid is the only type shown to help prevent neural tube defects [4].
People with the MTHFR 677 TT genotype average only about 16% lower blood folate on the same folic acid intake, and the CDC says intake matters more than genotype [4]. See our folate monograph for the forms side by side.
Choline: the nutrient prenatals leave out
The adequate intake for choline in pregnancy is 450 mg a day; about 90% to 95% of pregnant women fall short, and prenatal supplements typically contain little if any [5]. In a 2025 lab analysis of 47 prenatal products, only 12 listed choline on the label, and 5 of those contained more than 20% less than claimed [10].
Evidence for benefit is early: in a small controlled feeding trial of 26 women, those given 930 mg a day in the third trimester had infants with faster information-processing speed than those given 480 mg [6]. A large hard-boiled egg has about 147 mg [5]. More in our choline monograph.
DHA and omega-3s
A 2018 Cochrane review of 70 randomized trials with 19,927 women found omega-3 supplements or foods during pregnancy lowered preterm birth before 37 weeks (11.9% vs 13.4%) and early preterm birth before 34 weeks (2.7% vs 4.6%), both high-quality evidence [7].
The same review found slightly more pregnancies running past 42 weeks (2.6% vs 1.6%) and very few differences in children's cognition, IQ or vision [7]. See our omega-3 monograph.
Iodine
The iodine RDA rises from 150 to 220 mcg a day in pregnancy, and the American Thyroid Association and American Academy of Pediatrics recommend a daily supplement with 150 mcg when planning a pregnancy, pregnant or breastfeeding [8]. The upper limit for adults is 1,100 mcg a day [8].
In an analysis of 59 best-selling US prenatals, 34 contained iodine and 24% of prenatal doses sold had none; some used kelp, an iodine source known to be highly variable [9]. In the 2025 lab test, 20 of 25 products that listed iodine contained more than 20% less than the label claimed [10]. More in our iodine monograph.
Quick answers
Do I need methylfolate instead of folic acid if I have an MTHFR variant?
No, according to the CDC: people with MTHFR variants can process folic acid, and folic acid is the only form shown to help prevent neural tube defects [4].
How much choline do I need while pregnant?
The adequate intake is 450 mg a day in pregnancy and 550 mg while breastfeeding [5]. Most prenatals contain little, so check the label [5][10].
When should I start a prenatal vitamin?
The CDC advises starting 400 mcg of folic acid at least 1 month before trying to conceive [3].
More in Fertility & Prenatal
References
- [1]Folic Acid Supplementation to Prevent Neural Tube Defects: US Preventive Services Task Force Reaffirmation Recommendation Statement. JAMA, 2023.
- [2]Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet, 1991.
- [3]About Folic Acid (updated September 18, 2026). Centers for Disease Control and Prevention, 2026.
- [4]MTHFR Gene Variant and Folic Acid Facts (July 16, 2026). Centers for Disease Control and Prevention, 2026.
- [5]Choline: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2022.
- [6]Maternal choline supplementation during the third trimester of pregnancy improves infant information processing speed: a randomized, double-blind, controlled feeding study. FASEB J, 2018.
- [7]Omega-3 fatty acid addition during pregnancy (Cochrane review). Cochrane Database Syst Rev, 2018.
- [8]Iodine: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024.
- [9]Iodine Content of the Best-Selling United States Adult and Prenatal Multivitamin Preparations. Thyroid, 2019.
- [10]Content of selected nutrients and heavy metals in prenatal multivitamins and minerals: an observational study. Am J Clin Nutr, 2025.