New Guidance on Eating Fish During Pregnancy

Congratulations on your pregnancy! There is so much to know about eating well for a healthy pregnancy, but one question that comes up often is, "Can I eat fish?"

The short answer is yes, and it is highly recommended. But whether certain fish should be avoided and how this message is perceived is under intense debate. A recent 2022 study hopes to put this debate to bed.

In the past, mixed messages came out from nutrition authorities about fish during pregnancy, leaving women confused and avoiding fish altogether.

However, it's important to know that the recommendation is:

Eat 2-3 servings of fish per week during pregnancy.

(Hibbeln et al, 2019; Spiller et al, 2019; Dietary Guidelines for Americans 2020-2025).

Here's a simple recipe for Tahini Lemon Fish using any white fish.

A serving of fish is not a lot. Typically, a serving size is 4 oz. for anyone over the age of 10 years old. You can estimate 4 oz. by choosing a filet that's about the size of the palm of your hand.

1 serving = 4 oz = the size of the palm of your hand

Fish is important for children, too. For an infant 6 months to 1 year, small shredded pieces of fish is a good source of iron.

For children 1-3 years old, a serving is 1 oz. (or the size of the palm of their hand)

For children 4-7 years old, a serving is 2 oz.

For children 8-10 years old, a serving is 3 oz.

Fish is important for the fetus's brain development and growth. It provides vitamins, minerals, and lean protein that are especially important during pregnancy to ensure both mom and baby are healthy.

Some of the nutrients that fish provide during pregnancy, breastfeeding, and early childhood to support a child’s brain development include healthy fats, choline, zinc, vitamin D, iron, selenium, and iodine. (FDA)

Fish also offer protein and vitamin B12, nutrients important throughout the lifecycle.

The best fish choices during pregnancy include:

These fish have the most omega-3 fatty acids which contribute to neuro-development of the baby. They can also help the mother's iron stores and cardiovascular, eye, brain, and mental health (FDA).

New guidance on eating fish during pregnancy suggests a pregnant woman generally does not need to take on the added stress and confusion of trying to remember the seven fish the FDA recommends avoiding. So the short answer is no. However, read on to understand the risks scientists have found with high mercury levels.

For many years, the FDA has been publishing a chart of the best fish choices, fish to eat occasionally, and fish to avoid during pregnancy, breastfeeding, and childhood. The chart categories are based on the potential for mercury contamination in bigger fish.

However, this message has served to scare many pregnant and breastfeeding women away from eating any seafood during pregnancy, which as outlined above, can be detrimental to a baby's development due to vital nutrients found in fish.

Below is an explanation for experts' new recommendations based on three newer research studies. However, the FDA hasn't taken these studies into account and updated their guidance yet.

To understand the reason for the new recommendations, keep reading the summaries of the studies below.

However, if you're short on time or just want the 7 key points, here they are:

A study published in 2005 followed 135 pregnant women and their children after they were born in the US. They tracked the amount of fish the pregnant women ate in their second trimester and measured the mercury (Hg) in their hair at delivery. Then they tested the babies’ visual recognition memory (VRM) at 6 months of age.

Results: Mothers consumed an average of 1.2 fish servings per week during the second trimester.

The Good: Higher fish intake was associated with higher infant VRM test scores. For each additional weekly fish serving, babies’ VRM score was 4.0 points higher.

The Caution: However, an increase of 1 ppm in Hg was associated with a decrease in VRM score of 7.5 points.

VRM scores were highest among infants of women who consumed >2 fish servings per week, but had Hg levels ≤1.2 ppm. Higher fish consumption in pregnancy was associated with better infant cognition, but higher Hg levels were associated with lower cognition.

Conclusion: They concluded that women should continue to eat fish during pregnancy, but choose varieties with lower mercury contamination.

Four years later, a new study made researchers reconsider the effects of Hg on children's development. They followed 779 women in Seychelles, a population that consumes a lot of fish in their diet. The researchers compared the amount of fish the pregnant women consumed with the Hg they were exposed to and their children's IQ at 6-, 19-, 29-, 66-, and 107-months old.

The Good: In the Seychelles Child Development Study (SCDS), more exposure to Hg had a positive effect on males’ test performance at age 5 and 9 years old. The Hg exposure was mainly from fish, suggesting the nutrients in fish may have a protective effect against Hg's adverse effects.

The Caution: In the same study, recent postnatal exposure (not from pregnant mother's diet, but from child consuming fish) at 9 years old was linked to negative test scores for females.

Conclusion: No consistent pattern emerged to support a causal relationship between a pregnant woman's intake of fish, exposure to mercury, and a child's intelligence.

The most recent and largest study was published in NeuroToxicology in 2022. It reviewed blood and umbilical cord tissue from 12,000 pregnant women in the UK for Hg. The total blood mercury levels of the mother were compared with the pregnant woman’s reported dietary intake of 103 foods.

Results: The prenatal Hg levels were taken from the mother and showed about 9% of Hg in their blood was coming from fish. Mercury was also coming from wine, herbal teas, white bread, meat pies, pastries, French fries, and dental fillings.

At birth, the baby’s weight, length, and head circumference were measured. There was an association between Hg and these 3 measurements.

The Caution: It appeared that if the mom had Hg in her blood during pregnancy and did not eat fish, there were negative effects on these measurements at birth (meaning baby could be too big or too small compared to normal).

The Good: But if she had Hg in her blood and ate fish, the baby had more normal measurements.

The children were followed through adulthood.

The Caution: At 8 years old, they found that prenatal Hg levels were associated with higher scores related to autism.

The Good: However, if the mom ate fish at least 3 times per week, the child had no association with autism.

The Good: For IQ, there was no association between Hg levels and IQ. However, if moms ate fish during pregnancy, their child was more likely to have a high IQ.

The Good: Similarly, Hg didn’t seem to affect a child’s math and science abilities, but if the mother ate fish during her pregnancy, her child was more likely to do well in math and science.

Conclusion: The researchers of this study concluded that a woman’s Hg level during pregnancy is unlikely to have an adverse effect on the development of the child provided that the mother eats fish. Fish may have protective effects against mercury during pregnancy.

You can refer to the FDA chart below if interested in knowing which fish are likely to be contaminated with higher levels of mercury.

The FDA and EPA have worked together to determine (from small sample sizes) which fish are likely to contain higher levels of Hg. Their methods are listed on the FDA website and input from three reviewers were considered and incorporated to give the best guidance around fish they have seen with higher, moderate, and lower levels of Hg. They do not address the more recent 2009 Seychelles study nor 2022 ALSPAC study findings.

Check local and state advisories about fish caught locally. If there are no advisories available, the FDA suggests limiting carp, catfish, perch, and trout to only one serving a week and don't eat any other fish that week, as these tend to be higher in Hg or other contaminants. However, as we have learned from the research, mercury from fish is unlikely to have negative consequences for a fetus after they are born.

The NIH has taken into account the recent studies discussed here and their statement is as follows:

Seafood contains varying levels of methyl mercury. However, results from numerous studies, including a systematic review of the literature on maternal fish intake and subsequent neurodevelopmental outcomes, show that the health benefits of consuming moderate amounts of seafood during the prenatal period outweigh the risks.

Outside of the US, Professor Jean Golding, co-author and Emeritus Professor of Paediatric and Perinatal Epidemiology at the University of Bristol, and author of the 2022 UK study concludes:

There is no evidence of harm from… fish, but there is evidence from different countries that such advice can cause confusion in pregnant women. The guidance for pregnancy should highlight ‘Eat at least two portions of fish a week, one of which should be oily’ – and omit all warnings that certain fish should not be eaten.’

For help planning nutrition during your pregnancy, you can book an appointment with a Registered Dietitian at ZESTNutritionService.com.

Hibbeln, J.R.; Spiller, P.; Brenna, J.T.; Golding, J.; Holub, B.J.; Kris-Etherton, P., et al. (2019). Relationships between seafood consumption during pregnancy and childhood and neurocognitive development: Two systematic reviews. Prostaglandins, Leukotrienes and Essential Fatty Acids,151, 4-36. https://www.sciencedirect.com/science/article/pii/S0952327819301929

Spiller, P.; Hibbeln, J.R.; Myers, G.; Vannice, G.; Golding, J.; Crawford, M.A., et al. (2019). An abundance of seafood consumption studies presents new opportunities to evaluate effects on neurocognitive development. Prostaglandins, Leukotrienes and Essential Fatty Acids, 151, 8-13. https://www.sciencedirect.com/science/article/pii/S0952327819301966

U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.

U.S. Food & Drug Administration. (2018). Questions and Answers from the FDA/EPA Advice on What Pregnant Women and Parents Should Know About Eating Fish. FDA.gov.

https://www.fda.gov/Food/ResourcesForYou/Consumers/ucm534873.htm

Oken, E.; Wright, R.O.; Kleinman, K.P.; Bellinger, D.; Amarasiriwardena, C.J.; Hu, H., et al. (2005). Maternal fish consumption, hair mercury, and infant cognition in a U.S. cohort. Environmental Health Perspectives, 113:10. https://doi.org/10.1289/ehp.8041

Myers, G.J.; Thurston, S.W.; Pearson, A.T.; Davidson, P.W.; Cox, C.; Shamlaye, C.F., et al. (2009). Postnatal exposure to methyl mercury from fish consumption: A review and new data from the Seychelles Child Development Study, NeuroToxicology, 30(3), 338-349.

https://www.sciencedirect.com/science/article/abs/pii/S0161813X09000278

Golding, J.; Taylor, C.; Iles-Caven, Y.; and Gregory, S. (2022). The benefits of fish intake: Results concerning prenatal mercury exposure and child outcomes from the ALSPAC prebirth cohort, NeuroToxicology, 91, 22-30. https://www.sciencedirect.com/science/article/pii/S0161813X22000602

National Institutes of Health. (2018). Omega-3 Fatty Acids. NIH.gov. https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/#h7