Prenatal maternal stress in relation to the effects of prenatal lead exposure on toddler cognitive development

To evaluate the effects of maternal lead exposure during pregnancy on toddler cognitive development and the potential effect modification by maternal stress.

We conducted a prospective birth-cohort study in Shanghai from 2010 to 2012 and investigated 225 mother-infant pairs. The mothers were recruited in mid-to-late pregnancy and children were followed up until 24-36 months old. A self-administered Symptom Checklist-90-Revised Scale (SCL-90-R) was used to assess maternal emotional stress during pregnancy. Maternal whole blood lead levels were measured during gestational weeks 28-36. The toddlers' cognitive levels were assessed using the Gesell Development Scale. Multiple linear regression models were established to explore the main effects of prenatal lead exposure on toddlers' cognitive abilities and the modifying effects of maternal stress. Covariate information was collected through interviews, questionnaires and medical records.

The mean maternal blood lead concentration was 3.30 (95%CI: 3.05, 3.57) μg/dL. After adjusting for relevant confounders, no significant associations of maternal blood lead concentrations with toddlers' cognitive levels were observed in all five domains of the Gesell scale (P>0.05). However, the interaction between prenatal maternal blood lead and stress was significant in the domains of adaptive behavior, language and social behavior. When stratified by maternal stress levels, compared with non-significant associations (P>0.05) among low (P1-P75) prenatal stress group, adverse associations between maternal blood lead concentrations (log10-transformed) and toddlers' cognitive levels were observed among high (P75-P100) prenatal stress group in the domains of language (β=-33.82, 95%CI: -60.04, -7.59), social behavior (β=-41.00, 95%CI: -63.11, -18.89) and adaptive behavior (β=-17.93, 95%CI: -35.83, -0.03).

Prenatal maternal stress may exacerbate the deleterious effects of prenatal exposure to lead on toddler cognitive development.