LONGITUDINAL STUDY OR SERUM THYROID HORMONES, CHORIONIC GONADOTROPHIN AND THYROTROPHIN DURING AND AFTER NORMAL PREGNANCY

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Abstract
Measurements of serum levels of thyroxine (T4), free T4, 3,5,3''-triiodothyronine (T3), free T3, 3,3'',5''-triiodothyronine (reverse T3, rT3), thyroxine-binding globulin capacity (TBGcap), chorionic gonadotropin (hCG) and thyrotropin (TSH) were carried out prospectively in 8 women with uncomplicated pregnancies, to examine interrelationships between the thyroid gland and thyroid stimulating hormones during pregnancy. During pregnancy the levels of T4, free T4, T3, rT3 and TBGcap were significantly elevated, and TSH was decreased. It was noted that the elevation of T4 was maintained from the 8th-27th wk of gestation while the level of TBGcap progressively increased. The levels of free T4 and rT3 in the 1st and 3rd trimesters were significantly higher than those of age-matched, non-pregnant women. The levels of hCG showed a biphasic variation, with a peak in the 8th-15th wk, followed by a decline in the 2nd trimester and a small, secondary elevation in the 32nd-39th wk. This latter elevation was positively correlated with changes in free T4 and T3 levels. The increase of serum T4 accompanied by an increase of free T4 in the 1st trimester appeared due to augmented secretion of T4, rather than being secondary to the elevated levels of TBG-cap.