If a pregnant women takes radioactive iodine for thyroid cancer, the thyroid gland may be destroyed in the developing fetus. Infants whose mothers have taken such medicines should be observed carefully after birth for signs of hypothyroidism.
Most states require a routine screening test to check all newborns for hypothyroidism. See also: Newborn screening tests
Harris KB, Pass KA. Increase in congenital hypothyroidism in New York State and in the United States. Mol Genet Metab. 2007; 91(3):268-277.