The Influence of Toxic Metals on Small for Gestational Age

Abstract

Background/Purpose/Objectives: The purpose of this research is to determine the relationship between metal exposure during the first and third trimesters of pregnancy and the risk of small for gestational age (SGA). Size for gestational age is an important predictor of early childhood morbidity and mortality. Genetic polymorphisms in glutathione s transferase omega 1 (GSTO1) and pi 1 (GSTP1) were explored as possible effect modifiers of this relationship. Study Design/Methods: This research is nested within a larger study called The Maternal-Infant Research on Environmental Chemicals (MIREC) Study. The MIREC study is a biomonitoring study being conducted by Health Canada, the Sainte Justine hospital in Montreal, and clinical researchers from various other cities. The study population is a sample of 2000 pregnant women, recruited during the first trimester of pregnancy from across Canada between 2007 and 2011. Blood lead, cadmium, mercury and arsenic were all measured in the first and third trimesters of pregnancy. Arsenic in urine was measured in the first trimester. A log binomial regression model was used to investigate the relationship of interest. Product terms were used to explore the gene polymorphisms. Results: No association was found between blood lead, cadmium or arsenic and risk for SGA. Increased risk for SGA was observed between the ≤.0.8 µg/L and the ≥1.6 µg/L exposure groups for mercury (RR=1.56; 95% CI = 1.04-2.58) and, between the ≥22.56 µg/L and ≤.75 µg/L exposure groups for arsenobetaine (RR= 1.65; 95% CI = 1.10-2.47) after adjustment for the effects of parity and smoking. A marginally significant interaction was observed between the GSTP1 polymorphism and blood lead level in relation to risk for SGA (p for interaction =0.06). No other SNPs were found to modify the relationship between any metal exposure and SGA risk. Conclusions: These results suggest that increased levels of mercury in a pregnant woman’s blood or of arsenobetaine in a pregnant woman’s urine, are associated with giving birth to an infant that is SGA. These results are suggestive of increased risk for an adverse effect of low-level lead exposure during pregnancy on fetal size in those with the GSTP1A114V variant genotype.