Estudio de la función tiroidea y del estado de yodación de las mujeres embarazadas del área occidental de Cantabria

Abstract

Thyroid hormones play a crucial role at every stage of life including fetal period. Thyrotropin (TSH) and free fraction of thyroid hormones (fT4 and fT3) are the main tool for the diagnosis of thyroid disorders during pregnancy. But, pregnacy produces a series of profound physiologic changes in the mother that have a significant affect on maternal thyroid function. These changes can, in turn, complicate the interpretation of maternal thyroid function tests and make no valid the thresholds taken from nonpregnant population. In the abscense of specific reference thresholds the Endocrine Society (ES) and the American Thyroid Association (ATA) recommends the following trimester-specific reference ranges for TSH in pregnancy: 0,1-2,5 ?UI/l in fisrt trimester, 0,2-3,0 ?UI/l in second trimester and 0,3-3,0 ?UI/l in third trimester. This thresholds have been accepted by most endocrinology societies but its generalization may cause a high percentage of misclassification. The purpose of our study is to determine the specificic reference range for TSH in each trimester of gestation in the pregnant population of our health area and their iodine status. Methodology: Prospective longitudinal observational study of nonintervention. Results: 411 healthy pregnant women with normal thyroid function and negative thyroid antibodies were included. TSH, T4L and T3L were measured in first, second and third trimester of gestation. In addition, urine iodine concentration (UIC) was evaluated in 106 of the pregnant women in first and third trimester. The interval of TSH was 0,26-3,95 ?UI/ml in first trimester, 0,78-3,85 ?UI/ml in second trimester and 0,71-3,61 ?UI/ml in third trimester. Median urinary iodine was 171,31 ?g/l for the first trimester and 190,37 ?g/l for the third triemester showing an adequate iodine intake. Conclusions:The establishment of specific reference ranges during pregnancy it is crucial to avoid misclassification in the diagnosis of thyroid disorders in this population.