[Reference values for thyroid hormones in the population of pregnant women in Jaen (Spain)].

OBJECTIVE

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.

DESIGN

Descriptive study of pregnant women to define the ranges of normality of thyroid hormones in this population.

SETTING

Jaen and Osuna (Spain).

POPULATION

Healthy pregnant women.

METHODS

Thyroid hormone determination in the three trimesters of pregnancy in healthy women taking iodine supplements.

RESULTS

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 4.18μUI/ml in the first trimester, 1.78 and 3.89μUI/ml in the second and 2.01 and 4.30μUI/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.

CONCLUSION

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.