Effects of Prenatal Exposure to Mercury on Cognitive and Psychomotor Function in One-Year-Old Infants: Epidemiologic Cohort Study in Poland

Purpose The aim of the study is to assess the cognitive and psychomotor status of 1-year-old infants whose mothers were exposed to low, but varying, amounts of mercury during pregnancy. Methods Mercury levels in cord and maternal blood at delivery were used to assess prenatal environmental exposure to mercury. Bayley Scales of Infant Development were used to assess neurobehavioral health outcomes. The cohort consisted of 233 infants who were born at 33 to 42 weeks of gestation between January 2001 and March 2003 to mothers attending ambulatory prenatal clinics in the first and second trimesters of pregnancy. Enrollment included only nonsmoking women with singleton pregnancies between the ages of 18 and 35 years who were free from chronic diseases. Results The geometric mean (GM) for maternal blood mercury level for the group of infants with normal neurocognitive performance was lower (GM = 0.52 μg/L; 95% confidence interval [CI], 0.46–0.58) than that observed in the group with delayed performance (GM = 0.75 μg/L; 95% CI, 0.59–0.94), and this difference was significant (p = 0.010). The GM of cord blood mercury level in the normal group also was lower (GM = 0.85 μg/L; 95% CI, 0.78–0.93) than that observed in the group with delayed performance (GM = 1.05 μg/L; 95% CI, 0.87–1.27), and this difference was of borderline significance (p = 0.070). The relative risk (RR) for delayed performance increased more than threefold (RR = 3.58; 95% CI, 1.40–9.14) if cord blood mercury level was greater than 0.80 μg/L. Risk for delayed performance in the group of infants with greater maternal mercury levels (>0.50 μg/L) also was significantly greater (RR = 2.82; 95% CI, 1.17–6.79) compared with children whose mothers had mercury levels less than 0.50 μg/L. Conclusions The results may be of public health importance because delayed psychomotor or mental performance in infants is assumed to be an indicator of later neurocognitive development in children, which may persist into adult life.