Thyroid function in molar pregnancy.

Various aspects of thyroid hormone economy were examined in 15 patients with molar pregnancy and in 5 patients with choriocarcinoma. None of the patients with molar pregnancy was clinically thyrotoxic, though serum thyroxine (T4) was increased in 13 and free T4 concentrations were above normal in four of ten in whom measurements were made. In 2 patients with elevated serum T4 levels and in one patient with normal serum T4 levels, the daily rate of T4 disposal was increase, and most of 131I derived from 131I-T4 was excreted into urine in two patients in whom estimation of urinary excretion was made. Serum total triiodothyronine (T3) concentrations closely paralleled those of serum T4, but T3/T4 ratios were lower than those previously found in patients with toxic diffuse goiter of Graves' disease. Unresponsiveness to exogenous thyrotropin-releasing hormone (TRH) was observed in 5 patients with molar pregnancy whose serum total T4 and T3 levels were increased. Human chorionic gonadotropin (hCG) concentrations in serum ranged from 0.5 to 2830 IU/ml and were less than 200 IU/ml in 36% of the patients, possibly because molar pregnancy was diagnosed by ultrasonography, rather than high titers of urinary or serum hCG. Serum thyroid stimulating activity measured by the McKenzie bioassay closely paralleled values for hCG (r:+0.94). All thyroid abnormalities disappeared quickly after removal of the mole. In choriocarcinoma, no abnormality of thyroid function was found. These results suggest that: 1) some patients with molar pregnancy display a marked elevation of serum T4, T3, and free T4 concentrations, probably as a result of the action of a thyroid stimulator which is closely related to serum hCG or may be hCG itself; 2) T4 production rates are increased in these patients, and the pituitary responds to TRH in a manner similar to that found in thyrotoxicosis. Despite this, frank clinical thyrotoxicosis is usually absent, possibly because of relatively low serum T3/T4 ratios, possibly because of the limited duration of thyroid hyperfunction, and possibly because of other factors that for the present remain unknown.