Fish Intake in Maternal Diet, Mercury Exposure May Affect Fetal Growth

Laurie Barclay, MD

September 14, 2009

September 14, 2009 —- The amount and type of fish consumed by a pregnant woman and mercury exposure may affect fetal growth, according to the results of a prospective, population-based mother-infant cohort study reported in the August 26 Online First issue of the American Journal of Clinical Nutrition.

"Birth size has been shown to be related to maternal fish intake, although the results are inconsistent," write Rosa Ramón from the CIBER en Epidemiología y Salud Pública in Barcelona, Spain, and colleagues. "The objective was to assess the association of consumption of different types of fish and prenatal mercury exposure with birth weight, birth length, and classification as small for gestational age (SGA) in newborns."

From 2004 to 2006, cord blood total mercury level was measured in 554 newborns. Maternal fish consumption was classified in 4 frequency categories: less than 1 portion per month, 1 to 3 portions per month, 1 portion per week, and 2 or more portions per week.

Compared with newborns in the lowest quartile of total mercury exposure, those in the highest quartile weighed 143.7 g less (95% confidence interval [CI], –251.8 to –35.6; P for trend = .02) and had higher odds of being SGA for length (odds ratio [OR], 5.3; 95% CI, 1.2 - 23.9; P from likelihood ratio test = .03), after adjustment in multivariate models. No statistically significant linear relationship was observed (P for trend = .13).

Compared with mothers who consumed less than 1 portion of canned tuna per month, those consuming 2 or more portions per week had newborns who weighed more (P for trend = .03) and had a lower risk of having infants who were SGA for weight (P for trend = .01).

Consumption of 2 or more portions per week vs less than 1 portion per month of large oily fish was linked to greater risk of being SGA for weight and consumption of lean fish with a lower risk of being SGA for length, but there was no linear relationship in either case (P for trend > .05).

"The role of fish in fetal growth depends on the amount and type of fish consumed," the study authors write. "The findings for mercury warrant further investigation in other settings."

Limitations of this study include sample size limited by the availability of cord blood samples, possible unmeasured confounders, lack of data regarding exposures to other chemicals, food frequency questionnaire not validated in the study population, and possible misclassification of fish types.

"The potential effects of fish consumption on fetal growth should be taken into account when recommending fish consumption to pregnant women or those of childbearing age," the study authors conclude. "The inverse association between prenatal mercury exposure and birth size and the underlying biologic mechanisms warrant further investigation."

The Instituto de Salud Carlos III, Ministerio Sanidad y Consumo, Ministerio Educación y Ciencia supported this study. The study authors have disclosed no relevant financial relationships.

Am J Clin Nutr. Published online August 26, 2009. Abstract


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