Fish oil

Does fish oil during pregnancy lower the risk of preterm birth?

Updated 4 Nov 2026

Short answer

It may, and women with low omega-3 levels seem most likely to benefit.[1] A 2018 Cochrane review found 11% fewer preterm births and 42% fewer early preterm births.[2] A later trial of 5,486 pregnancies found no fall in early preterm birth overall.[3]

What the Cochrane review found

The 2018 Cochrane review included 70 trials and 19,927 women.[2] It rated these results as high-quality evidence:[2]

  • birth before 37 weeks: 11.9% with omega-3 against 13.4% without[2]
  • birth before 34 weeks: 2.7% against 4.6%[2]
  • low birth weight: 14.0% against 15.6%[2]

Pregnancies lasted about 1.7 days longer on average.[2] Pregnancies past 42 weeks probably became more common, 2.6% against 1.6%.[2] Children showed very few differences in thinking, vision, language or growth.[2]

What later studies changed

The ORIP trial in Australia gave 900 mg of omega-3 a day, from before week 20 until week 34.[3] Early preterm birth was 2.2% with fish oil and 2.0% with vegetable oil, with no significant difference.[3] Babies who were very large for their age at birth were more common with fish oil.[3]

An exploratory analysis of the same trial looked at omega-3 levels in early pregnancy. Women with low levels had 70% lower odds of early preterm birth with fish oil.[1] An analysis like this one can suggest a group that benefits, but it does not prove it.[1]

A 2022 statement from the International Society for the Study of Fatty Acids and Lipids included the newer trials and still found 12% fewer preterm and 35% fewer early preterm births.[4] A 2016 US government report found longer pregnancies and slightly higher birth weight, but no effect on the risk of premature birth.[5]

What guidelines say

The groups below give amounts for pregnancy:[4]

  • EFSA: 100 to 200 mg of DHA a day on top of the 250 mg of EPA and DHA for all adults[4]
  • US FDA and the American College of Obstetricians and Gynecologists: 8 to 12 ounces of lower-mercury seafood a week[4]
  • A guideline in an obstetrics journal: 600 to 1000 mg of EPA and DHA, or DHA alone, for women with low DHA intake (under 150 mg a day). It starts no later than week 20[4]

Trials gave different amounts. Two US trials gave 600 mg of DHA a day, as 3 capsules, or vegetable oil. Women who took more capsules had less early preterm birth and low birth weight.[6]

Other effects on the child

In one trial, women took 2.4 g of omega-3 a day from week 24. Persistent wheeze or asthma in their children was 16.9% against 23.7% over 3 years.[7] Other trials have not all agreed, and more research is needed.[4] Results of trials on child brain development and vision are not consistent either.[4]

Who should be careful

Cod liver oil also gives vitamins A and D, which can be harmful in excess.[5] Fish oil supplements have not been found to contain methylmercury, but some seafood does, so US agencies advise lower-mercury fish in pregnancy.[4] Women who are pregnant or planning a pregnancy should ask a doctor or midwife about any supplement.[5]

What is still unknown

The open question is who benefits. Results point to women who start with low omega-3 levels, but most clinicians do not test omega-3 status.[1][4] The Cochrane authors called for follow-up of children and for a better view of how results differ by dose and type of omega-3.[2]

Sources (7)

  1. Identifying women who may benefit from higher dose omega-3 supplementation during pregnancy to reduce their risk of prematurity: exploratory analyses from the ORIP trial. Yelland LN, Sullivan TR, Gibson RA, Simmonds LA, Thakkar SK, Huang F, et al. BMJ Open, 2023. PMID 37068907
  2. Omega-3 fatty acid addition during pregnancy. Middleton P, Gomersall JC, Gould JF, Shepherd E, Olsen SF, Makrides M Cochrane Database Syst Rev, 2018. PMID 30480773
  3. A Randomized Trial of Prenatal n-3 Fatty Acid Supplementation and Preterm Delivery. Makrides M, Best K, Yelland L, McPhee A, Zhou S, Quinlivan J, et al. N Engl J Med, 2019. PMID 31509674
  4. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  5. Omega-3 Supplements: What You Need To Know. NIH National Center for Complementary and Integrative Health, 2024. www.nccih.nih.gov
  6. Dose-response relationship between docosahexaenoic acid (DHA) intake and lower rates of early preterm birth, low birth weight and very low birth weight. Carlson SE, Gajewski BJ, Alhayek S, Colombo J, Kerling EH, Gustafson KM Prostaglandins Leukot Essent Fatty Acids, 2018. PMID 30392575
  7. Fish Oil-Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring. Bisgaard H, Stokholm J, Chawes BL, Vissing NH, Bjarnadóttir E, Schoos AM, et al. N Engl J Med, 2016. PMID 28029926

More about fish oil

What is fish oil?Does fish oil reduce inflammation?How much EPA and DHA is in a fish oil capsule?Is eating fish better than taking fish oil?What is fish oil used for?Should fish oil be taken with food?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.