Can Women Eat Fish During Pregnancy?

In a NY Times article “Should Pregnant Women Eat More Tuna?”, the advantages and disadvantages of eating fish are discussed. The article explains that fish consumption is beneficial to the development of a fetus and nursing infant, and acknowledges a report that argues that the benefits far outweigh the risks. However, the article also mentions the risk of mercury exposure when consuming fish. Exposure to mercury causes tremendous effects in neurodevelopment -- and fish like tuna contain large amounts of mercury. Yet, we know fish fulfill many of the necessary dietary requirements for pregnant women, but is it worth the risk? This article will evaluate the risks and benefits of fish consumption on a fetus in order to potentially better help individuals determine whether or not pregnant women should eat fish.

Fish contain omega-3 fatty acids -- nutrients that humans are unable to synthesize. There are two omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and they are even more critical during pregnancy. DHA is a necessary structural component of the brain and the retina, and maximum uptake of DHA is seen during the second half of gestation. Animal studies have shown that lack of DHA during pregnancy is associated with irreversible visual and behavioral deficits. Since this revelation, nutrient guidelines for pregnant women have included a minimum consumption of DHA. Studies with women and DHA consumption have been difficult to evaluate considering the ethical reasons behind preventing pregnant women from consuming DHA, as well as confounding variables such as breastfeeding. Yet consumption of DHA has never met with any significant adverse effects, as well as providing visual and cognitive development of infants. Unfortunately, most fish do not only contain DHA, but also methyl mercury due to recent developing environmental conditions.

Methyl Mercury is a neurotoxin that is prominent in the environment, formed through microbial action from inorganic mercury deposited in aquatic environments. Due to biomagnification, or the consumption of organisms up the food chain, the concentration of methyl mercury is highest in large fish. Exposure to extreme amounts of methyl mercury causes neurological damage as well as fatalities in adults. Furthermore, the fetus is more sensitive to the adverse effects of methylmercury. In the 1950’s and 60’s, neurotoxins polluted the local water in Japan and the fish contained much more methyl than usual. The noted effects on the developing central nervous system (CNS) initiated the realization of the dangers of methyl mercury. After the exposure in Japan, in the winter of 1971 there was an outbreak of methyl mercury poisoning in Iraq, and an association between damage of developing CNS was suggested. These occurrences of exposure show the potential influence of fish consumption on child development.

In 1989, a prospective longitudinal cohort study was done on methylmercury exposure and found that no adverse outcomes at 66 months were associated with prenatal or postnatal exposure. This study examined carefully the impact of methyl mercury exposure with a large amount of tests. The study also presented advantages such as that the cohort was in Seychelles, an island with high fish consumption. In the study, mothers consumed a mean of 1.3 fish meals daily. The study concluded that maternal dish consumption through 107 months of age had no adverse developmental effects. Adverse effects in attention, mood, language, cognition, and neuropsychologic function were still not obviously detected, despite the large consumption of methyl mercury. Lastly, a study taking place in the United Kingdom analyzed umbilical cord blood from 1024 mothers and found no significant increase in methylmercury levels between mothers consuming fish once every two weeks and those consuming fish four times a week. These studies and extensive data on human subjects contests the belief that consumption of fish should be limited or stopped due to methyl mercury concentration in large fish.

The conflicting findings of the benefits and risks of fish consumption have lead to uncertainty in providing advice to pregnant women. Recommending fish oil capsules as a replacement for whole fish have been shown to not achieve the same results as consuming whole fish. Perhaps because whole fish are more bioactive, and the other nutrients within fish, such as selenium and iodine, are also important. Additionally, women who are advised not to consume high mercury fish by their physician may just avoid all fish consumption, which is also unideal. Many women in a study done in 2009 in Boston were aware of mercury in fish, and few were advised to eat fish or knew what DHA was. A National Health and Nutrition Examination from 1999-2002 survey found that the mean DHA was only 73 mg/d among pregnant women, compared to the recommended 200 mg/d. Recommending all fish, however, provides the possibility that women will consume large amounts of high mercury fish. The dilemma that is reached once physicians and medical providers specify which fish to eat is that pregnant women begin to avoid all fish. The solution, as stated in the NY Times article, the Food and Drug Administration advises pregnant women not to consume high-mercury fish. Avoiding these fish, and consuming others low in methyl mercury, such as salmon, can benefit women. 

References:

Bloomingdale A, Guthrie LB, Price S, Wright RO, Platek D, Haines J, Oken E. A qualitative study of fish consumption during pregnancy. The American Journal of Clinical Nutrition. 2010;92:1234–40. 

Bramante CT, Spiller P, Landa M. Fish Consumption During Pregnancy. JAMA Pediatrics. 2018;172:801. 

Davidson PW, Myers GJ, Cox C, Axtell C, Shamlaye C, Sloane-Reeves J, Cernichiari E, Needham L, Choi A, Wang Y, et al. Effects of Prenatal and Postnatal Methylmercury Exposure From Fish Consumption on Neurodevelopment. Jama. 1998;280:701. 

FDA Fish Advice: Technical Information [Internet]. EPA. Environmental Protection Agency; 2018 [cited 2018Nov21]. Available from: https://www.epa.gov/fish-tech/epa-fda-fish-advice-technical-information .

Koletzko B, Cetin I, Brenna JT. Dietary fat intakes for pregnant and lactating women. British Journal of Nutrition. 2007;98. 

Levin ED, Buccafusco JJ. Animal models of cognitive impairment. Boca Raton: CRC/Taylor & Francis; 2006. 

Mahaffey KR. Methylmercury Exposure and Neurotoxicity. Jama. 1998;280:737. 

Myers GJ, Davidson PW, Strain JJ. Nutrient and Methyl Mercury Exposure from Consuming Fish. The Journal of Nutrition. 2007;137:2805–8. 

Nesheim MC, Yaktine AL. Seafood choices: balancing benefits and risks. Washington, D.C.: National Academies Press; 2007. 

Oken E, Belfort MB. Fish, Fish Oil, and Pregnancy. Jama [Internet]. 2010;304:1717.

Schober SE. Blood Mercury Levels in US Children and Women of Childbearing Age, 1999-2000. Jama. 2003;289:1667.