Maternal heavy metal exposure may lead to reduced birthweight
Maternal exposures to heavy metals vanadium (V), arsenic (As) and lead (Pb) at early pregnancy appear to result in lower maternal free T3 (FT3) and FT3/free T4 (FT4) ratio, which may contribute to reduced birthweight, suggests a recent study.
“Mediation analyses indicated that maternal thyroid hormone was a possible mediator of the association between urinary heavy metals and birth size,” the authors said.
Maternal urinary V was inversely associated with FT3 and FT3/FT4 ratio levels, while urinary As and Pb were inversely associated with FT3. Moreover, maternal FT3 and FT3/FT4 ratio were positively associated with birthweight.
In mediation analyses, maternal FT3 or FT3/FT4 ratio appeared to facilitate 5.33–30.57 percent of the associations among V, As and Pb levels and birth size.
“Maternal thyroid hormones during pregnancy play a critical role in foetal development,” according to the authors.
In an earlier study involving Chinese pregnant women, an inverse association was also found between thyroid hormone concentrations and levels of heavy metals (ie, As, manganese and antimony). [Environ Int 2018;121:1185-1192]
The current cohort study conducted in China measured the concentrations of heavy metals in urine samples and thyroid hormones in blood samples of 675 pregnant women during early pregnancy. Multivariable linear regressions were used to examine the associations of maternal urinary heavy metal levels with both maternal thyroid hormones and birth outcomes.
In addition, the authors performed mediation analyses to evaluate the mediation role of thyroid hormones in these associations.