URINARY IODINE EXCRETION DURING NORMAL-PREGNANCY IN HEALTHY WOMEN LIVING IN THE SOUTHWEST OF FRANCE - CORRELATION WITH MATERNAL THYROID PARAMETERS

A prospective study was undertaken to evaluate urinary iodine excretio n and changes of maternal thyroid function during pregnancy in healthy women living in the southwest of France. The cohort included a total of 347 pregnant women (mean age 28.0 +/- 0.5 years). Iodine concentrat ion in a random urine sample and thyroid tests (free thyroxine [FT4], free triiodothyronine [FT3], thyrotropin (TSH), thyroxine-binding glob ulin [TBG], and thyroglobulin [Tg]) were measured at initial presentat ion (before 12 weeks of gestation), and during the ninth month of preg nancy. A thyroid ultrasound was performed 1 to 5 days after delivery i n 246 mothers. Mean urinary iodine levels were low during the first tr imester (6.9 +/- 0.4 mu g/dL), as well as during the ninth month of pr egnancy (8.6 +/- 0.6 mu g/dL). During pregnancy, FT4 and T-3 concentra tions decreased (p < .001), and TSH and Tg concentrations increased (p < .001). Thyroid hypertrophy (thyroid volume greater than 18 mL) was present in 15.4% of women whose first trimester urinary iodine concent ration was less than 5 mu g/dL, but was present in only 3.5% of women whose urinary iodine concentration was greater than 10 mu g/dL. A goit er (thyroid volume greater than 22 mL) was present in 11% of the mothe rs. In conclusion, this prospective study shows that urinary iodine ex cretion is low in pregnant women living in the southwest of France. Th is low iodine intake is associated with reduced circulating thyroid ho rmone levels and growth of the thyroid gland. These data point to the need of an increased iodine supply in these pregnant women to reduce t he potential consequences of low iodine intake on maternal thyroid eco nomy.