Endocrine Abstracts

Evaluation of the thyroid function in pregnant women is of extreme importance for maternal and neonatal health. The reference interval of thyroid function tests in pregnant women differs from that of the general population and among trimesters in the same patient. Trimester-specific thyrotropin (TSH) reference ranges for pregnant women are recommended in order to avoid misclassification of the thyroid dysfunction during pregnancy.

Less data about the free thyroxin (FT4) trimester-specific reference range is available.

In order to test the variability of free thyroxin we performed a prospective pilot study.

41 consecutive pregnant women with abnormal thyroid function tests were selected for this study. There were excluded the patients with known hypothyroidism before pregnancy (3), the patients diagnosed with Basedow disease (5) and the patients in the third trimester of pregnancy because of the low number of cases (4).

We stratified the women in two groups according to TSH values as having normal thyroid function or subclinical hypothyroidism (SCH). Non parametric tests revealed no significant differences for free thyroxine between the two groups when analyzed by trimester of pregnancy or as a whole. We found a negative correlation between free thyroxine and body weight in the 2^nd trimester for the SCH.

Different reports about the variability of free thyroxine along the pregnancy should consider the body weight of the patient along with iodine supply and the laboratory methodology.