Prenatal exposure to mercury and child fine motor development in an Eastern Mediterranean cohort

Abstract

Introduction. We argue that the evidence about a relation between maternal total mercury (THg) and child fine motor (FM) neurodevelopmental scores remains insufficient. To fill this gap, we analyzed data from a prospective mother-child cohort recruited in Italy, Slovenia, Croatia and Greece within PHIME, EU Sixth FP. Methods. Study design and rationale of the study is described in Valent F et al J Epidemiol 2013;23(2):146-152. Varying by country, mothers were recruited during pregnancy or at child’s birth. Metals were measured in maternal hair and blood during pregnancy and in umbilical cord blood and breast milk. FM scores were calculated by a psychologist using Bayley III at 18 months. For this analysis we defined the exposure as higher quintiles of mother’s hair THg levels (ng/g) and the outcome as the lowest quintile of the scaled FM score (<=10). Lifestyle, dietary and socioeconomic factors assessed by questionnaires were considered as potential confounders or effect modifiers. Multivariate logistic regression models were run against FM as binary outcome. Results. 2189 mothers were enrolled in the study during pregnancy. 1729 mother-child pairs provided information at child’s birth. Follow-up at 18 months was 85%. Mother’s hair THg quintiles cut-offs were 337, 566, 881,1456 ng/g. The odds ratio (OR) of an FM score <= 10 for THg ≥ 337 ng/g was 2.04 (95% confidence interval: 1.33-3.21), adjusted for country, sex, breastfeeding duration and earlier introduction of fresh fish in the child’s diet. Results were consistent by country but did not show clear trends. Earlier introduction of fresh fish in child’s diet was linked with higher FM scores (p<0.0245). Conclusions. Absence of a trend for THg level and use of a dichotomous FM outcome variable require caution. However, these results suggest further testing of this hypothesis in existing child cohorts that consider the relation of mercury with FM scores separately from gross psychomotor assessments.