Prenatal and Neonatal Peripheral Blood Mercury Levels and Autism Spectrum Disorders

Background: Prenatal and early-life exposures to mercury via vaccination, diet, and other sources have been hypothesized to be associated with increased risk of autism spectrum disorders (ASD).

Objectives: We investigated the association between ASD and levels of total mercury measured in maternal serum from mid-pregnancy and infant dried bloodspots from the newborn period.

Methods: The study sample was drawn from the Early Markers for Autism (EMA) Study, a population-based case-control study designed to evaluate biomarkers for ASD. Cases were children with ASD (n=84), identified from the California Department of Developmental Services (DDS). General population controls (GP) (n=160) were randomly sampled from birth certificate files and frequency matched to cases by gender, birth month, and birth year.  A second group of controls included children with mental retardation or developmental delay (DD) (n=49) identified from DDS.  Maternal serum specimens and newborn bloodspots were retrieved from the California Department of Public Health prenatal and newborn screening specimen archives. Serum levels of total mercury were measured in ng/mL by the Agilent 7500 Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Logistic regression was used to estimate risk of ASD associated with log-transformed maternal serum and infant blood mercury levels. 

Results: Maternal serum and infant blood mercury levels were significantly correlated among both cases and controls (R~0.4, P<0.05).  In maternal serum, the geometric mean mercury levels were similar for ASD cases (0.46 ng/mL), GP controls (0.30 ng/mL) and DD controls (0.33 ng/mL) and case-control comparisons were unchanged after adjustment for maternal age, race/ethnicity, place of birth, gestational age, and mother's weight prior to blood draw (ASD vs. GP: Adj. Odds Ratio (AOR)= 0.99, 95% Confidence Interval (CI) 0.75, 1.29); ASD vs. DD: AOR=1.33, 95% CI 0.81, 2.20).  Likewise, in newborn blood, no differences in geometric mean mercury levels were detected for ASD cases vs. GP controls (3.37 ng/mL vs. 2.61 ng/mL, p=0.33), and adjustment for maternal age, maternal race/ethnicity, place of birth, infant age at blood collection, gestational age at birth, and plate number did not alter results (AOR=1.11, 95% CI 0.89, 1.37). While newborn blood mercury levels were somewhat higher for ASD cases vs. DD controls (3.37 ng/mL vs. 2.16 ng/mL, p=0.049), this difference did not persist after adjustment for covariates (AOR = 1.26, 95% CI 0.80, 1.99).

Conclusions: Levels of total mercury in serum collected from mothers during mid-pregnancy and in blood collected from infants at birth were not associated with risk of ASD.