Changes in thyroid function and serum iodine levels after prepartum use of a povidone-iodine vaginal lubricant

To determine if application of iodide to vaginal mucosa of pregnant women results in significant iodide absorption or changes in thyroid function, we studied 18 intrapartum women for whose examinations during labor povidone-iodine gel was used as a lubricant and 16 for whose examinations an iodine-free lubricant was used. Both serum inorganic iodine and total serum iodine increased significantly (p<0.001) after iodide exposure and fell (p=0.003) to near baseline within two days. In both groups, serum thyroxine and triiodothyronine fell during labor and delivery; differences between groups were not significant. In the iodine-treated group, however, there was a significant increase in thyroid-stimulating hormone at two days postpartum (p<0.001). Iodide applied to vaginal mucosa of pregnant women is absorbed and affects the maternal pituitary-thyroid axis.