Quick answer

NIH says it is not clear whether omega-3 supplements taken during pregnancy affect a baby's health or development. A Cochrane review of 70 trials in 19,927 women found fewer births before 37 weeks and more pregnancies lasting past 42 weeks. Anyone who is pregnant should ask a doctor before starting any supplement.^1,2

Key facts

NIH says it is not clear whether EPA and DHA supplements taken during pregnancy or breastfeeding affect a baby's health or development.¹
In a Cochrane review of 70 trials with 19,927 women, pregnancy lasted past 42 weeks in 2.6% of women given omega-3s and 1.6% of women who were not.²
FDA and EPA advise 2 to 3 servings a week of fish from their lower-mercury Best Choices list during pregnancy, at 4 ounces a serving.³
The label of a prescription omega-3 medicine says published data are not enough to identify a risk of major birth defects or miscarriage.⁴
Cod liver oil supplements also provide vitamin A, and NIH says too much preformed vitamin A in pregnancy can cause birth defects.^5,6

What do NIH and FDA say about omega-3 and pregnancy?

NIH's fact sheet for consumers is direct about the gap. It says it is not clear whether taking dietary supplements with EPA and DHA during pregnancy or breastfeeding affects a baby's health or development. What it does describe is eating seafood: 8 to 12 ounces a week, picking types that are higher in EPA and DHA and lower in mercury, such as salmon, herring, sardines and trout.¹

FDA and the Environmental Protection Agency give the same kind of advice in more detail for fish. During pregnancy and breastfeeding they advise 2 to 3 servings a week from their Best Choices list, or 1 serving from the Good Choices list, with a serving measured as 4 ounces. That advice is about eating fish, not about taking capsules.³

NIH's fact sheet for health professionals adds that trials of EPA and DHA supplements in pregnancy have not shown consistent effects on a child's thinking or vision. It also lists advice from several professional groups, which differ from one another in what they suggest beyond seafood.⁵

What did the Cochrane review of pregnancy trials find?

The largest summary of trials is a 2018 Cochrane review. It pooled 70 randomized trials with 19,927 women, in supplements and in foods, compared with placebo or no omega-3. The table shows the results most relevant to safety, with the review's own rating of how sure the evidence is.²

Selected results from the 2018 Cochrane review of omega-3 in pregnancy²
Outcome	What the review found	Certainty
Birth before 37 weeks	11.9% with omega-3 and 13.4% without (26 trials, 10,304 women)	High
Birth before 34 weeks	2.7% with omega-3 and 4.6% without (9 trials, 5,204 women)	High
Pregnancy lasting past 42 weeks	2.6% with omega-3 and 1.6% without (6 trials, 5,141 women)	Moderate
Large-for-gestational-age babies	A possible small increase (risk ratio 1.15, range 0.97 to 1.36)	Moderate
Serious adverse events in the mother	Too few data to say (2 trials, 2,690 women)	Low

In plain terms, the trials found fewer early births and more late ones, and the authors said the supplements probably increase the number of pregnancies that run past 42 weeks. The authors added that the trials mostly measured outcomes around birth, and that longer follow-up of the mothers and children is still needed.²

Do cod liver oil or fish carry other concerns in pregnancy?

Not every omega-3 oil is the same product. NIH notes that cod liver oil supplements provide vitamin A and vitamin D as well as omega-3s, and its vitamin A fact sheet says that people who are or might be pregnant should not take high-dose supplements of preformed vitamin A.^5,6

Too much preformed vitamin A in pregnancy can cause birth defects, including malformations of the eye, skull, lungs and heart.^6,7

Mercury is a separate question. Fish contain varying amounts, which is why FDA and EPA sort fish into choices by mercury level. For supplements, NIH's professional fact sheet says they have not been found to contain methyl mercury, because it is removed in processing.^3,5

What does a prescription omega-3 label say about pregnancy?

A prescription omega-3 medicine is a different product from a supplement, but its label is one of the few official documents to address pregnancy directly. It says the available case reports and safety reports are not enough to identify a drug-associated risk for major birth defects, miscarriage or other outcomes for mother or baby. In animal studies, no harm to offspring was seen at doses up to 5 times the maximum human dose in rats. In one rat study at 7 times that dose, live births fell by 20% and pup survival by 40%, and in rabbits at 4 times that dose, which also made the mothers ill, there were skeletal changes and slower fetal growth.⁴

Its patient leaflet tells people to talk to their healthcare provider if they are pregnant or plan to become pregnant, and says it is not known if the medicine will harm an unborn baby.⁴

Who should ask a doctor before taking omega-3 in pregnancy?

Anyone who is pregnant or planning a pregnancy should ask a doctor or midwife before adding a supplement, and the questions below are worth bringing along.¹

The Cochrane finding on pregnancies that lasted past 42 weeks, and what it could mean for the pregnancy.²
Whether the oil is fish oil, algal oil or cod liver oil, because cod liver oil adds vitamin A.^5,6
Any allergy to fish or shellfish, since it is not known whether people with these allergies react to omega-3 made from fish oil.⁴
Any blood thinner or aspirin, or any bleeding problem, because high doses of omega-3s may affect bleeding.¹
A vegetarian or vegan diet, where the Dietary Guidelines for Americans, as listed in NIH's table, advise talking to a healthcare provider about whether EPA and DHA are needed.⁵

Questions people ask

Is omega 3 fish oil safe during pregnancy?

NIH says it is not clear whether fish oil supplements affect a baby's health or development, and the Cochrane review found both fewer early births and more pregnancies lasting past 42 weeks. The sources do not settle the question, so ask your doctor before starting.^1,2

Is 1000mg omega 3 safe during pregnancy?

NIH describes a typical fish oil supplement as 1,000 mg of oil that contains about 180 mg of EPA and 120 mg of DHA, and the trials in the Cochrane review used many different products and amounts. No source here singles out a 1,000 mg capsule, so ask your doctor or pharmacist about the one you have.^2,5

Is omega 3 ok during pregnancy?

FDA and EPA advise 2 to 3 servings a week of fish from their lower-mercury list during pregnancy, and NIH names salmon, herring, sardines and trout as types higher in EPA and DHA. For supplements, ask your doctor.^1,3

Is omega 3 oil safe during pregnancy?

Oils differ. Fish oil and algal oil provide omega-3s on their own, while cod liver oil also adds vitamin A, and NIH says too much preformed vitamin A in pregnancy can cause birth defects. Ask your doctor or pharmacist to read the label of any oil you are considering.^5,6

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This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.