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Fish oil in pregnancy

Goal: To lower the risk of preterm birth: what trials gave pregnant women, from when, and who seems to benefit most.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Updated 4 Nov 2026
Dose

900 mg of omega-3 a day in the ORIP trial, and 600 mg of DHA a day in two US trials.[1][2] A guideline gives 600 to 1000 mg of EPA and DHA or DHA alone for women with low DHA intake.[3]

Form

Fish oil capsules in ORIP, against vegetable oil.[1] DHA capsules in the US trials.[2]

When to take

From before week 20 until week 34 in ORIP.[1] The guideline says to begin no later than week 20.[3]

How long

About 14 weeks or more, from before week 20 until week 34.[1]

What studies found

A Cochrane review of 70 trials found preterm birth at 11.9% against 13.4% and early preterm birth at 2.7% against 4.6%.[4] ORIP then found early preterm birth at 2.2% against 2.0%, with no significant difference.[1] In its exploratory analysis, women with low omega-3 levels had 70% lower odds of early preterm birth.[5]

Ask a doctor first

Pregnancies past 42 weeks probably became more common with omega-3, 2.6% against 1.6%.[4] Cod liver oil also gives vitamins A and D, which can be harmful in excess.[6]

Women who are pregnant or planning a pregnancy should ask a doctor, midwife or pharmacist first.[6]

References

  1. 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
  2. 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
  3. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  4. 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
  5. 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
  6. Omega-3 Supplements: What You Need To Know. NIH National Center for Complementary and Integrative Health, 2024. www.nccih.nih.gov