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Smarting from Fish? Seafood Consumption and Pregnancy
By Russell H. Greenfield, MD, Dr. Greenfield is Clinical Assistant Professor, School of Medicine, University of North Carolina, Chapel Hill, NC, and Visiting Assistant Professor, University of Arizona, College of Medicine, Tucson, AZ; he reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
Source: Hibbeln JR, et al. Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): An observational cohort study. Lancet 2007;369:578-585.
Abstract: An observational cohort study (part of the Avon Longitudinal Study of Parents and Children, or ALSPAC, originally designed to evaluate the impact of environmental factors both during and after pregnancy on childhood well-being) was performed to assess the possible risks and benefits to childhood development associated with different levels of maternal seafood intake during pregnancy. Expectant mothers in and around Bristol, United Kingdom, were sent questionnaires four times during pregnancy and then at specified times after childbirth to obtain data about diet, social circumstances, education, and behavioral and developmental outcomes (the latter specifically at ages 6, 18, 39, 42, and 81 months). Data regarding food consumption were obtained at 32 weeks gestation via self-completed food-frequency questionnaire (three questions focused on seafood intake, and intake levels of omega-3 fatty acids were derived from results). Children's abilities were estimated using the Denver Developmental Screening Test, with scales completed by mothers at home at 6, 18, 30, and 42 months. A questionnaire eliciting information on children's strengths and difficulties was completed at age 81 months by participating mothers.
In sum, 12% of women ate no fish during pregnancy, while 65% ate 1-340 g/week and 23% ate more than 340 g/week. Unadjusted data showed that children of mothers who ate no fish had a greater risk of adverse or suboptimal outcomes. Higher maternal fish intake was non-linearly associated with a lowered risk of suboptimal verbal IQ. Analysis of adjusted data showed that consumption of seafood during pregnancy was significantly associated with a lowered risk of suboptimal score on nine of 23 outcomes. There was no evidence of harm to the offspring (relative to child behavior or development) of mothers who ate more than three servings of fish per week during pregnancy. Instead, intake of more than 340 g of seafood per week was apparently beneficial for a child's neurodevelopment. The authors concluded that advice to limit seafood consumption during pregnancy to minimize fetal mercury exposure might significantly reduce intake of nutrients essential for optimal neurodevelopment.
U.S. governmental agencies have recommended since 2004 that expectant mothers should limit intake of seafood to 340 g/week to minimize fetal exposure to neurotoxins like mercury. The recommendation to limit seafood intake during pregnancy creates a conundrum, however, as the major dietary source of omega-3 fatty acids, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), is fish, and prior reports have strongly suggested that low maternal omega-3 fatty acid intake during pregnancy is associated with low childhood verbal IQ. Fetal mercury exposure clearly results in harm, and that risk has been deemed greater than the potential benefit obtained from regular ingestion of fish and associated nutrients. The results of this trial throw that perspective into question.
The trial was very well done and considered many potential confounding factors including smoking and alcohol use, but conclusions are limited to a degree by the observational nature of the trial. Type of fish ingested, geographic source of the fish, and portion sizes could only be estimated, and the potential for reporting bias is very real considering that mothers filled out questionnaires about their own children. Regardless, the results are compelling, and the recommendation of the authors not to follow the 2004 U.S. guidelines on fish intake during pregnancy throws down the gauntlet. What should we practitioners recommend to our patients?
At present, the best course of action would appear to be to recommend regular fish intake during pregnancy, but to focus on those species with low risk of mercury contamination. Fish to enjoy include Alaskan salmon, herring, sardines, rainbow trout, and sablefish (black cod); fish to avoid, on the other hand, include large predatory species like shark, swordfish, king mackerel, and tilefish, also called golden snapper or golden bass (see Sidebar for a detailed listing of ocean-friendly and safe fish choices).
Additionally, a recommendation to eat more fish during pregnancy brings up a question of social justice, as the authors point out that mothers with the lowest levels of education (a surrogate for socioeconomic status) also had the lowest levels of fish intake and the highest rate of study attrition. For reasons both ethical and moral, such a disparity must somehow be corrected.