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Omega-3 in Pregnancy: DHA Doses, Food and Safe Supplements

· Irina Shtern · MSc Nutrition (Middlesex University) · BANT-registered nutritional therapist · CNHC registered

Pregnant woman serving cooked salmon at home

Most UK guidance points to the same plan: eat one to two portions of oily fish a week, and consider a supplement providing DHA if you eat little or no fish. Typical figures are 100 to 200 mg of DHA a day on top of normal intake, or around 450 mg of EPA plus DHA. Avoid cod liver oil and anything containing vitamin A (retinol). Below, we explain what the numbers mean, how to hit them with food, and what to check on a label.

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TL;DR

Table of Contents

Why omega-3 matters in pregnancy

Omega-3 fatty acids are fats your body cannot make in useful amounts. The one that matters most here is DHA. According to the NIH Office of Dietary Supplements, DHA is concentrated in the brain and retina and accumulates most rapidly during the third trimester.

The WHO notes that pregnancy is a time of higher risk of low omega-3 status, because your own stores tend to fall as they are used for the developing baby. That is why a steady intake from the first trimester onwards makes sense, rather than leaving it until late pregnancy.

How much DHA and omega-3 do you need?

Different bodies give different figures, because they answer slightly different questions. Here they are side by side.

Source Recommendation
EFSA, as reported by HSIS 100 to 200 mg DHA a day on top of general adult requirements
BDA, as reported by HSIS A supplement providing 450 mg EPA plus DHA a day
EBCOG position statement, 2024 350 to 450 mg omega-3 a day in pregnancy; about 600 to 1,000 mg DHA plus EPA a day for women at increased risk of preterm birth, started before 20 weeks and continued to around 37 weeks
ISSFAL statement, 2022 About 1,000 mg DHA plus EPA to reduce early birth risk, preferably starting before 20 weeks

A 2024 review in Frontiers in Nutrition summarises international expert guidance in the same way: at least 250 mg a day of DHA plus EPA before pregnancy, with an extra 100 to 200 mg of DHA during it, ideally starting in the second trimester and continuing to about 37 weeks.

The higher doses are aimed at women with a higher risk of early birth, and that is a decision for your midwife or obstetrician, not something to self-prescribe. For most women, the lower figures are the sensible target.

Does omega-3 reduce the risk of preterm birth?

The strongest evidence is here. A 2018 Cochrane review of 70 randomised trials found that increasing long-chain omega-3 intake lowered the risk of preterm birth (before 37 weeks) by 11%, from 134 to 119 per 1,000 births. Early preterm birth (before 34 weeks) fell by 42%, from 46 to 27 per 1,000.

The ISSFAL statement adds that women who start out low in omega-3 benefit most. That is a practical point: if your diet already includes oily fish most weeks, you are not starting from the same place as someone who eats none.

Getting omega-3 from food

Food comes first. The BDA says pregnant women can safely eat up to two portions of oily fish a week, a portion being 140 g fresh fish or one small can. Oily fish includes salmon, mackerel, sardines and trout. Fresh, tinned and frozen all count, with the exception of tinned tuna, which does not count as oily fish.

The limit exists because oily fish can contain low levels of pollutants that build up in the body (BDA). Avoid shark, swordfish and marlin entirely because of mercury.

Fish is not something to fear in pregnancy. A UK birth cohort study found that moderate mercury levels were not associated with adverse birth outcomes, and encouraged eating fish in line with government guidelines.

Other DHA sources, per HSIS, include white fish such as cod and haddock (in smaller amounts), algae oil, and eggs from hens fed an omega-3 enriched diet.

A simple week of omega-3

If you are vegetarian or vegan, plant foods such as flaxseed and walnuts supply ALA, but as conversion to DHA is very limited, an algae-based DHA supplement is the more direct route.

Choosing a safe supplement

The NHS advises against cod liver oil and any supplement containing vitamin A (retinol) in pregnancy, because too much can harm the baby’s development. Always read the label. The Scientific Advisory Committee on Nutrition (SACN) advises that total vitamin A from food and supplements should not exceed 1,500 µg a day.

A quick label check:

  1. Is it fish body oil or algae oil, not fish liver oil?
  2. Does it show how many milligrams of DHA (and EPA) per daily serving?
  3. Is there any added vitamin A or retinol? If so, put it back.
  4. Does it fit alongside your prenatal multivitamin? Many already contain some DHA, so check you are not doubling up unnecessarily.

The EBCOG statement says omega-3 intake appears to be safe in pregnancy, with no harmful upper limit established. If you take medication, have a bleeding condition, or have epilepsy, speak to your GP or midwife first. The Epilepsy Society also notes that large amounts of vitamin A from liver and fish oil supplements such as cod liver oil can harm an unborn baby.

What about DHA and autism?

A frequent worry, and the evidence is reassuring. A cohort consortium analysis found an inverse association between eating fish in pregnancy and autism diagnosis in children, comparing any fish intake with none. This kind of study shows association, not cause, but it gives no reason to avoid fish or DHA.

Do you need a test?

The Frontiers review notes that women with low intake could be identified with a short set of questions about diet, and that blood DHA testing has been proposed but still lacks standardised methods and cut-offs. In practice, a careful look at what you eat each week tells you most.

Our perspective

In our consultations, omega-3 is rarely the only question. Women arrive tired, nauseous, unsure what to eat in the first trimester, or worried about iron, and a single capsule cannot solve that. We look at the whole picture: how often you eat oily fish, what your appetite allows, any vegetarian or vegan choices, and what your prenatal vitamin already contains.

Then we turn that into a plan that fits your week, not a generic list. We are registered with BANT and CNHC and hold an MSc in Nutrition, and we work alongside your midwife or doctor, never instead of them. Personalised guidance is especially useful if you have a digestive condition, diabetes risk or a history of early birth.

Irina

Support from Foodconnection

If you would like help building omega-3, iron and the rest of your prenatal nutrition into everyday meals, we offer personalised consultations in London and online. An initial consultation of one and a half hours with written personalised recommendations costs £150, and 12 weeks of dedicated support costs £250. See the full list of prices or our services.

Foodconnection

For wider reading, our prenatal nutrition checklist, our guide to first trimester nutrition and our article on iron-rich pregnancy foods cover the neighbouring questions.

FAQ

Is an omega-3 supplement safe in pregnancy?

Omega-3 from fish body oil or algae oil appears to be safe, and no harmful upper limit has been established (EBCOG). The risk lies in the wrong product: avoid cod liver oil and anything with vitamin A. Tell your midwife what you take.

When should I start taking DHA?

Expert guidance suggests starting preferably in the second trimester and no later than about 20 weeks, continuing to around 37 weeks. Starting earlier, or before conception, is also reasonable if you are eating little fish.

Do I need a DHA supplement if I eat salmon?

If you eat one or two portions of oily fish a week, you may already be covering much of what is recommended. A supplement is most relevant if you eat no oily fish, are vegetarian or vegan, or have been advised you are at higher risk of preterm birth.

Do babies need DHA supplements?

Babies get DHA through breast milk or fortified formula, and your own intake affects the DHA in your milk. HSIS notes that EFSA’s advice covers lactating women too. Talk to your health visitor before giving a baby any supplement.

Sources

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Educational overview; not a substitute for medical diagnosis.