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, 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. Animal model data suggest that with insufficient DHA during brain development, neuron growth and synaptic development are diminished.
The Lancet published results from the Avon Longitudinal Study of Parents and Children (ALSPAC) in 2007. 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.
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. 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.
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.
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. This is partly because of confusion about mercury resulting from media coverage of the FDA/EPA guidance and because physicians reinforce these concerns.
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.
In conclusion, women should try to eat fish regularly, especially fish types higher in DHA such as salmon, trout, herring, sardines, and Atlantic mackerel. Up to 6 oz of albacore tuna is great, but they should avoid shark, king mackerel, tilefish, and swordfish, as well as raw fish such as sushi or ceviche. It is also wise to check local advisories regarding self-caught fish in lakes and streams and to consume only fish that has been fully cooked. If a women is unable to eat 2 to 3 servings of fish per week, she should take an omega-3 DHA supplement as a secondary alternative; however, whole fish consumption is preferred to supplementation because the best evidence for beneficial impact comes from studies that involve whole food consumption with its complete nutritional content.
For more information and related science, visit the Perinatal Nutrition Working Group, a program of the National Healthy Mothers, Healthy Babies Coalition, at http://www.hmhb.org/pnwg/.