In 12 nonpregnant women, total iodine, protein-bound iodine, inorganic iodine, and thyroxine values were measured in serum before and 15, 30, 45, or 60 minutes after a two-minute vaginal disinfection with povidone-iodine (Betadine). Only 15 minutes after application, serum iodine levels were raised and remained significantly elevated 30, 45, and 60 minutes after disinfection. Serum concentrations of total iodine and inorganic iodine were increased up to fivefold to 15-fold, respectively; during the relative short period of observation, thyroxine levels were not altered. An overload of iodine can suppress thyroid hormonogenesis, and the fetal and neonatal thyroid glands are especially sensitive. In pregnant women, vaginitis should not be treated with povidone-iodine because of the possible development of iodine-induced goiter and hypothyroidism in the fetus and newborn. The risk is especially high when povidone-iodine is used repeatedly.
Vorherr H, Vorherr UF, Mehta P, Ulrich JA, Messer RH. Vaginal Absorption of Povidone-Iodine. JAMA. 1980;244(23):2628–2629. doi:10.1001/jama.1980.03310230030018