In particular, since the usual incidence of PDA is only 1 in 2000 births, and exposure to arsenic levels > 10 μg/L was previously reported to increase this incidence by only 75% [36], our study cohort is too small to detect an association of PDA with arsenic exposure or PRDM6 gene expression. Here, PRDM6 is linked to Patent ductus arteriosus.