According to an epidemiologic study published in the journal Environment International , fish consumption during pregnancy could harm child cognitive development as a result of methylmercury contamination. The study, undertaken in Krakow, Poland, examined variability in prenatal mercury exposure due to fish intake in pregnant women and followed infant psychomotor development over the first three years of life.

In total 374 infants born between January 2001 and March 2003 to mothers attending clinics were assessed. Weekly amounts of fish consumption were ascertained, together with measurement of blood mercury levels in the umbilical cord. Bayley Scales of Infant Development (BSID-II) were used to gauge the mental (MDI) and psychomotor developmental index (PDI) in children at 12, 24 and 36 months of age.

Results revealed a positive correlation between the amount of fish consumed in the first two trimesters of pregnancy and umbilical cord mercury concentrations, and suggest that mercury exposure negatively affects child psychomotor development.

The study abstract is available here.