Mom's fatty fish intake tied to baby's birthweight

By Anne Harding

NEW YORK (Reuters Health) - Pregnant women may want to limit their consumption of fatty fish like salmon and herring, according to study from Scandinavia that found that women who reported the highest consumption of these types of fish were at heightened risk of having small babies. There was no link between eating leaner fish and fetal growth.

Persistent organic pollutants such as polychlorinated biphenyls (PCBs) and DDT tend to accumulate in fatty tissue, so contamination of fatty fish with these substances could explain the findings, Dr. Thorhallur Ingi Halldorsson of the Statens Serum Institut in Copenhagen and colleagues note in the American Journal of Epidemiology.

While women who are pregnant and have been heavy consumers of fatty fish shouldn't be alarmed, since the relationship is "not particularly strong," the link should also not be ignored, Halldorsson told Reuters Health.

He advised: "Levels of contamination vary between regions and to be careful, they should read the local dietary guidelines on fish consumption and modify their diet accordingly. In most cases a modification but not dramatic changes should be enough to be on the safe side."

In prior studies, consumption of fish contaminated with mercury and other pollutants has been tied to reduced fetal growth and other problems.

Halldorsson's team set out to investigate the relationship between fish consumption and fetal growth based on whether the fish was fatty or lean. They surveyed 44,824 Danish women who had given birth between 1996-2002, asking them how frequently they ate certain foods. Most ate no fatty fish; consumption of lean fish was more common.

Women who ate more than 60 grams of fatty fish daily, or the equivalent of about two servings a week, were 24 percent more likely to have infants in the bottom tenth of weight for their gestational age than women who consumed 5 grams of fatty fish or less daily, or less than one serving a month.

The women with heavy fatty fish consumption were also 21 percent more likely to have infants with head circumferences in the bottom tenth for their gestational age.

As mentioned, contamination of fatty fish with organic pollutants could explain the relationship, the researchers say, while mercury is less likely to be a factor given that it's found in lean fish as well as fatty fish.

"Pregnant women should eat fish regularly," Halldorsson said, "but they should eat fish of varying type. "Since there are studies showing slight adverse effects, the important thing for pregnant women is to be on the safe side and regular (non extreme) fish consumption ensures sufficient amount of omega-3 fatty acids."

SOURCE: American Journal of Epidemiology, September 15, 2007.