Should I take DHA during pregnancy?
DHA is worth getting in pregnancy, and fish is the best place to start: 8 to 12 ounces a week of low-mercury fish. If you eat little or no fish, ask your doctor about a fish oil or algal DHA supplement. Across 70 trials, omega-3 in pregnancy cut early preterm birth by 42%, most clearly in women who eat little fish.
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The short answer: get DHA, from fish or a supplement
DHA (docosahexaenoic acid) is a long-chain omega-3 fat. The NIH says it is concentrated in the brain and the retina, and it builds up fastest in the third trimester. Researchers estimate that in the last trimester a baby stores about 50 mg of DHA every day. That DHA crosses the placenta from your blood, and your blood gets it from what you eat.
So the question is less "should I?" and more "where will mine come from?" For most women the first answer is fish. A supplement fills the gap when fish doesn't happen.
Why the brain wants DHA
DHA is built into the walls of brain cells and the light-sensing cells of the eye. The eye's share is mostly in place by birth. The brain keeps collecting DHA for about the first two years of life.
Your body can turn the plant omega-3 in flax, chia and walnuts (called ALA) into DHA, but the NIH puts the conversion rate at under 15%. Its fact sheet says eating EPA and DHA directly, from food or supplements, is the only practical way to raise your levels. Walnuts are still good food. They just can't stand in for salmon.
Fish brings more than DHA. The FDA lists omega-3 fats, iron, iodine and choline among the nutrients in fish that support a baby's brain. In a UK study of 11,875 pregnant women, eating no seafood was linked with a higher chance that the child scored in the lowest quarter for verbal IQ at age 8, compared with eating more than 12 ounces a week.
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How much fish covers it
The FDA and EPA advise 8 to 12 ounces (about 225 to 340 g) a week of lower-mercury fish in pregnancy and while breastfeeding. That's 2 to 3 servings from the Best Choices list. A serving is 4 ounces, about the size of your palm. Our fish guide has the full lists.
Not all fish carry the same DHA. Per 3 ounces cooked, using NIH figures:
| Fish | DHA (approx.) |
|---|---|
| Salmon | 1,220-1,240 mg |
| Herring | 940 mg |
| Sardines, canned | 740 mg |
| Atlantic mackerel | 590 mg |
| Rainbow trout | 440 mg |
| Canned light tuna | 170 mg |
| Cod | 100 mg |
Two 4-ounce servings of salmon a week work out to roughly 460 mg of DHA a day, averaged over the week. Two servings of cod come to about 40 mg a day. Both are healthy meals, but make at least one weekly serving a fatty fish like salmon, sardines, herring, mackerel or trout. Light tuna counts too; see canned tuna in pregnancy.
When a supplement makes sense
Maybe fish makes you queasy right now, or you're vegetarian, vegan or allergic. That's where a supplement earns its place, and its strongest evidence is about something every parent cares about: carrying the baby to term.
A 2018 Cochrane review pooled 70 randomized trials with 19,927 women. Taking omega-3 fats in pregnancy cut early preterm birth (before 34 weeks) by 42%, from about 46 to 27 babies per 1,000. It cut low birthweight by about 10%. The reviewers rated the evidence as high quality. Reaching term matters for the brain, because the last weeks are when it grows fastest.
The best results came from 500 to 1,000 mg of long-chain omega-3 a day, with at least 500 mg as DHA, starting around 12 weeks. The benefit looked biggest for women who started with low omega-3, which usually means women who eat little fish. That's why the higher doses in expert guidelines are aimed at women with low intake. If you already eat plenty of fish, more isn't always better, so your dose is worth a talk with your doctor.
What official groups suggest varies. The European Food Safety Authority suggests an extra 100 to 200 mg of DHA a day in pregnancy. A clinical guideline and the European obstetricians' board (EBCOG, 2024) suggest 600 to 1,000 mg of DHA plus EPA a day for women with low intake, starting by 20 weeks.
Fish and capsules each bring something. The child-development links come from women who ate fish, which brings DHA along with iodine, choline, iron and protein. The capsules' best-proven gift is helping more babies reach term and get those last weeks of brain growth. Fish most weeks, plus a supplement if you eat little fish, uses both strengths.
Fish oil or algal oil, and how to read the label
- Fish oil. The NIH notes that omega-3 supplements haven't been found to contain methylmercury, because it's removed during processing.
- Algal oil. DHA made by algae, which is where fish get it in the first place. It suits vegetarians, vegans and people allergic to fish. Doses are usually 100 to 300 mg DHA, and a small study found algal DHA was absorbed as well as DHA from cooked salmon. See vegetarian choline and DHA.
- Skip cod liver oil. It contains vitamin A as retinol, which the NHS advises against in pregnancy.
On the label, ignore the big "fish oil" number on the front. Find the DHA line in milligrams, check the serving size, and look for an independent seal such as USP Verified, NSF Certified or IFOS. Side effects are usually mild: a fishy aftertaste, heartburn or an upset stomach. Taking it with a meal may help.
Do this
- Write two fish nights on this week's calendar, and make one of them salmon, sardines, herring, mackerel or trout.
- Turn over your prenatal and any DHA softgel and note the DHA milligrams per serving.
- Stock two cans of salmon or sardines and two cans of light tuna for busy nights.
- If you eat little or no fish, ask your doctor or midwife this week about fish oil or algal DHA and how much.
- Check that your omega-3 supplement isn't cod liver oil and has no added vitamin A (retinol).
When to ask your doctor
Check with your doctor or midwife first if…
- You take a blood thinner or any other prescribed medicine.
- You have a fish allergy (ask about algal oil instead).
- You already eat plenty of fish, since you may need a lower dose or none (ask what fits you).
- You have a medical reason to limit fish.
Call your doctor now if…
- You have vaginal bleeding, fluid leaking or regular painful contractions.
- Your baby is moving less than usual, or the pattern changes (call now, day or night).
- You have severe belly pain that doesn't go away.
This page is general information, not medical advice. Every pregnancy and every child is different. Ask your doctor, midwife or pediatrician before changing supplements, diet or care.
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People also ask
Is DHA in my prenatal enough?
Check the DHA line. Some prenatals come with a separate DHA softgel; others don't. Compare the number with how much fish you eat. If you eat 2 to 3 servings of low-mercury fish a week, including a fatty fish, you may need less. Ask your doctor what total makes sense for you.
When should I start taking DHA?
In the Cochrane review, the best results came from supplements starting around 12 weeks. A European guideline for women with low intake says to start by 20 weeks and continue to about 37 weeks. Fish is fine from day one. Ask your doctor about timing for a supplement.
Does DHA help my baby's brain?
DHA is built into the brain and eyes, and your baby collects it fastest in the third trimester. Eating fish in pregnancy is linked to better child verbal and development scores, and omega-3 supplements help more babies reach term, when the brain grows fastest. That's a good reason to get enough, from fish or a supplement your doctor suggests.
Is fish oil safe from mercury?
The NIH notes that omega-3 supplements haven't been found to contain methylmercury, because it's removed during processing and purification. Choose a product with a third-party seal, and avoid cod liver oil in pregnancy because of its vitamin A.