To evaluate thyroid function in the three trimesters of pregnancy in healthy women taking iodine and to define the reference ranges of normality in this population.
Descriptive study of pregnant women to define the ranges of normality of thyroid hormones in this population.
Jaen and Osuna (Spain).
Healthy pregnant women.
Thyroid hormone determination in the three trimesters of pregnancy in healthy women taking iodine supplements.
A total of 429 pregnant women taking iodine supplements to maintain urinary iodine levels within the normal range were included. T4-l levels were between 0.60 and 1.06 in the first trimester, between 0.43 and 0.85 ng/dl in the second and between 0.40 and 0.82 ng/dl in the third. Thyroid stimulating hormone (TSH) reference values were between 0.23 and 4.18 渭UI/ml in the first trimester, 1.78 and 3.89 渭UI/ml in the second and 2.01 and 4.30 渭UI/ml in the third. T3-l values were between 2.33 and 3.84 pg/ml in the first trimester, between 2.04 and 3.51 pg/ml in the second and between 1.99 and 3.46 pg/ml in the third.
Bearing the 3rd and 97th percentiles in mind, the reference ranges in our population were far below those recommended by our reference laboratory. In view of these results, these values should be redefined to avoid incorrect diagnoses of hyperthyroxinemia in healthy pregnant women.