How much fish should I eat during pregnancy?

Key Points

During your first prenatal visit with Katherine Smith, a 26-year-old woman at 6 weeks' gestation, you cover the basics for maintaining a healthy pregnancy. You talk about a variety of issues such as exercise and prenatal vitamins. You also discuss how much weight to gain and the importance of eating a balanced diet to optimize nutrition and avoid excess weight gain. As you wrap up your visit, she says, "Oh, by the way, I've heard concerns about fish. How much fish should I eat during pregnancy?"

Many pregnant patients are confused about the potential risks of eating fish and turn to you for advice about whether they should eat fish during pregnancy. Fish consumption during pregnancy has created a significant amount of discussion among scientists, policymakers, and healthcare professionals. Although fish may be one of the most important foods for pregnant women to eat, concerns have been voiced regarding its safety, almost solely related to environmental mercury contamination.

FDA/EPA guidance

1. Do not eat shark, swordfish, king mackerel, or tilefish.

2. Eat up to 12 oz (2 average meals) per week of a variety of fish and shellfish that are lower in mercury, including shrimp, canned light tuna, salmon, pollock, and catfish. Albacore tuna has more mercury than canned light tuna; therefore, eat only 6 oz or less of albacore tuna per week.

3. Check local advisories about the safety of fish caught in local lakes, rivers, and coastal areas. If no advice is available, eat 6 oz or less per week of fish caught from local waters, and do not eat any other fish during that week. (See: http://www.epa.gov/waterscience/fish/states.htm.)

The FDA/EPA recommendations were derived primarily from a toxicologic perspective and a desire to minimize exposure to mercury. Although the FDA/EPA guidance intended to encourage fish consumption, pregnant women and the general population heard, "Stop, do not eat fish." As a result, fish consumption has declined.² Many healthcare providers also took a "better safe than sorry" approach when discussing fish with their patients. What we now know is that there can be neurodevelopmental benefits to the babies of women who eat fish that need to be considered in this discussion.³

Since 2004, many leading scientists have reassessed the FDA/EPA guidance to determine whether it was balanced or if important information had been lost in a well-intentioned effort. The result is a robust body of science that has emerged on benefits of eating fish during pregnancy, including better cognitive outcomes for newborns and children as well as likely reductions in preterm labor and peripartum depression. As clinicians, we need to ask whether our patients understand these benefits of eating fish. Do they know which fish to eat to help improve their pregnancy outcomes?

Fish benefits mother and baby

One reason that fish is such an important food for pregnant women is that it is the primary dietary source for omega-3 fatty acids, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Humans cannot make these nutrients; they need to consume them. The developing fetus and breastfeeding infant are entirely dependent upon the mother's omega-3 intake.

Eating fish 2 to 3 times per week helps mothers meet their need for DHA and EPA intake,¹ while providing other vital nutrients such as vitamins B and D, iron, and selenium. Fatty fish typically are higher in DHA content. The role of omega-3 fatty acids in neurologic development is likely why eating fish during pregnancy is linked to improved brain development, including cognition, vision, social/behavioral skills, language/communication skills, and motor skills in babies.⁴ Animal model data suggest that with insufficient DHA during brain development, neuron growth and synaptic development are diminished.⁵

The Lancet published results from the Avon Longitudinal Study of Parents and Children (ALSPAC) in 2007.⁴ This study followed 5,449 babies born in Bristol, England, for 8 years. Researchers observed that mothers who ate fish while pregnant had smarter children than those who did not. The study went on to say that limiting fish may be detrimental to a child's brain development. These findings have led the United Kingdom to reevaluate its current fish intake limits for pregnant women.

The American Journal of Clinical Nutrition published a separate study in March 2008 with similar results. This study was designed to determine whether low omega-3 DHA levels among some pregnant women can result in poor infant development. Researchers concluded that if wo-men eat too little food containing omega-3 DHA, it may negatively affect their infants' development, including their eyesight.⁶

Fish also is good for mothers. It has been associated with reduced preterm labor and perinatal depression. In a Norwegian study, prematurity rates among women were compared against high and low fish intake. It was noted that eating fish twice or more a week was associated with a lower risk of preterm birth.⁷ Additionally, omega-3 DHA has been shown to help prevent peripartum depression. Pregnant mothers in the ALSPAC study who ate no seafood were nearly 50% more likely to have depression symptoms than those who ate seafood at least 3 times per week.⁸

Eating whole foods such as fish makes it easier for women to maintain a balanced diet. Plant sources of omega-3 (eg, walnuts, canola oil, and flaxseed) contain a-linolenic acid (ALA), a short-chain omega-3 fatty acid. Most women's bodies inefficiently convert ALA to DHA, and for some there is no conversion at all.⁹

Despite fish's clear benefits, most women eat too little of it. On average, according to one national (but nonrepresentative) survey, pregnant women eat less than 2 oz of fish per week, while nonpregnant women eat less than 3 oz per week.¹⁰ This is partly because of confusion about mercury resulting from media coverage of the FDA/EPA guidance¹¹ and because physicians reinforce these concerns.¹²

Instead, prenatal DHA supplements or DHA-fortified food sources such as eggs and infant formula have been commercially endorsed. Although this approach is popular with some patients and their physicians, it ignores the complex nutritional benefits of eating the whole food.