Omega-3 and Fish Oil in Pregnancy: Is It Safe?

Written by Dr Mark Wilshere and Dr Marc Crutchley, GMC-registered GPs and founders of Dr Marks. Medically reviewed by Dr Mark Wilshere MBChB MRCGP DCH BSc (Hons).

The short answer: eating fish in pregnancy is encouraged, including oily fish, but the NHS advises no more than 2 portions of oily fish a week, and avoiding shark, swordfish and marlin. Don't take cod liver oil or other fish liver oils, because they're high in vitamin A, which can harm your baby. The NHS doesn't include omega-3 supplements in its routine pregnancy supplement advice (that's folic acid and vitamin D). If you're thinking about taking a fish oil supplement, talk to your midwife or GP first.

Why omega-3 matters in pregnancy

Long-chain omega-3 fats, mainly EPA and DHA, are found in oily fish. The NHS says long-chain omega-3 is important if you're pregnant or breastfeeding, because it can help your baby's nervous system to develop. The British Dietetic Association (BDA) also lists supporting the healthy development of your baby during pregnancy and breastfeeding among the reasons omega-3 matters.

Most of us don't eat as much fish as recommended, so it's worth looking at your diet first.

How much fish can you eat when pregnant?

The NHS advice for anyone who is pregnant, trying to get pregnant or breastfeeding is:

Oily fish (such as salmon, trout, mackerel, sardines and herring): no more than 2 portions a week. A portion is about 140g. This is because oily fish can contain pollutants that may build up in the body.
Tuna: if you're pregnant or trying for a baby, no more than 4 medium cans or 2 tuna steaks a week, because tuna contains more mercury than other fish. Tuna doesn't count as oily fish. There's no limit on tuna while breastfeeding.
Shark, swordfish and marlin: don't eat these if you're pregnant or trying to get pregnant, because they can contain levels of mercury that may damage a developing baby's nervous system.
Raw shellfish and raw fish (including sushi made with raw fish) should be avoided in pregnancy, and smoked fish should be cooked until steaming hot.

Cooked fish and cooked shellfish are fine to eat.

Why not cod liver oil?

Fish liver oils, such as cod liver oil, are different from fish oils made from the body of the fish. They're high in vitamin A (retinol). The NHS advises not taking cod liver oil or any supplement containing vitamin A in pregnancy, because too much vitamin A can harm your baby's development. The NHS also advises avoiding liver and liver products, such as pâté.

Always check the label. Some multivitamins and some omega-3 products contain vitamin A. The NHS guide to vitamin A explains more.

What does the research show about omega-3 supplements?

A large Cochrane review in 2018 looked at 70 trials involving nearly 20,000 pregnant women, comparing omega-3 (from supplements or food) with no omega-3. It found:

fewer babies born before 37 weeks: about 12 in 100 with omega-3, compared with about 13 in 100 without
fewer babies born before 34 weeks: about 3 in 100 with omega-3, compared with about 5 in 100 without
a probable increase in pregnancies lasting beyond 42 weeks, and possibly a small increase in larger babies

The reviewers rated the preterm birth evidence as high quality, but many other outcomes were lower quality. Women in the trials varied, and nearly half the trials included women at higher risk of complications.

UK guidance hasn't changed as a result: the NHS pregnancy supplement advice covers folic acid and vitamin D, and the BDA says omega-3 supplements aren't recommended for the general UK population. If you have questions about your own risk of preterm birth, or about omega-3, please ask your midwife or obstetrician rather than starting a supplement on your own.

If your midwife agrees to a supplement

If you and your midwife or GP decide a supplement is right for you, these checks help:

No vitamin A or retinol, and no fish liver oil
A sensible dose. The BDA suggests choosing an amount similar to what 1–2 portions of fish a week would provide, about 450mg of EPA and DHA a day for adults.
Suitability for your diet. Many fish oil capsules use gelatine, so they may not suit vegetarians. The BDA notes that some supplements contain only algae oil, so they're suitable for vegetarians.
Medicines. Tell your midwife if you take a blood thinner or other regular medicines.

If you don't eat fish

You can still get some omega-3 from plant foods such as linseed (flaxseed), rapeseed oil, walnuts, chia seeds and omega-3-enriched eggs, although these provide a different form (ALA), which the body converts to EPA and DHA only in small amounts. The NHS has more on fish and shellfish in pregnancy, and our food tips have ideas for a varied diet.

Further reading on our blog:

When to see your GP or midwife

Speak to your midwife or GP if you:

are thinking about taking any supplement in pregnancy, including fish oil
have taken cod liver oil or a vitamin A supplement and have just found out you're pregnant
have been told you're at higher risk of preterm birth
don't eat fish and are worried about your diet
take a blood thinner or other regular medicines

Frequently asked questions

Can I take fish oil while pregnant?

The NHS warns specifically against fish liver oils, such as cod liver oil, because they're high in vitamin A. It doesn't include omega-3 in its routine pregnancy supplement advice, so talk to your midwife or GP before taking any fish oil.

Is cod liver oil safe in pregnancy?

No. The NHS advises not taking cod liver oil or any supplement containing vitamin A when pregnant, because too much vitamin A can harm your baby.

How much oily fish can I eat when pregnant?

No more than 2 portions a week (about 140g each). Avoid shark, swordfish and marlin, and limit tuna to 4 medium cans or 2 steaks a week.

Does omega-3 in pregnancy help the baby's brain?

The NHS says long-chain omega-3 can help your baby's nervous system develop. Eating oily fish within the limits is the main way UK guidance suggests getting it.

Is it safe to take omega-3 while breastfeeding?

The same oily fish limit (2 portions a week) applies while breastfeeding, but there's no limit on tuna. Check with your health visitor, GP or pharmacist before taking a supplement.

References

NHS. Fish and shellfish (eating fish while trying to get pregnant, and during pregnancy and breastfeeding). https://www.nhs.uk/live-well/eat-well/food-types/fish-and-shellfish-nutrition/ (accessed 19 October 2026)
NHS. Foods to avoid in pregnancy. https://www.nhs.uk/pregnancy/keeping-well/foods-to-avoid/ (accessed 19 October 2026)
NHS. Pregnancy vitamins and supplements. https://www.nhs.uk/pregnancy/keeping-well/pregnancy-vitamins-and-supplements/ (accessed 19 October 2026)
British Dietetic Association. Omega-3: food fact sheet. https://www.bda.uk.com/resource/omega-3.html (accessed 19 October 2026)
British Dietetic Association. Pregnancy and diet: food fact sheet. https://www.bda.uk.com/resource/pregnancy-diet.html (accessed 19 October 2026)
Middleton P, Gomersall JC, Gould JF, Shepherd E, Olsen SF, Makrides M (2018). Omega-3 fatty acid addition during pregnancy. Cochrane Database of Systematic Reviews 11:CD003402. https://pubmed.ncbi.nlm.nih.gov/30480773/ (accessed 19 October 2026)
NHS. Vitamins and minerals: vitamin A. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-a/ (accessed 19 October 2026)

This article is general information and is not a substitute for personal medical advice. If you are pregnant, planning a pregnancy or breastfeeding, speak to your midwife, GP or pharmacist before taking any supplement. Food supplements should not replace a varied, balanced diet and healthy lifestyle. Dr Marks is an independent company and is not affiliated with or endorsed by the NHS.