THYROID FUNCTION IN ORAL CONTRACEPTION

Abstract

ABSTRACT Eighty one euthyroid, fertile women were treated cyclically with a daily dose of 5 mg of 6-methyl-6-dehydro-17α-acetoxyprogesterone (megestrol acetate) + 0.1 mg of 17α-ethynyl-oestradiol-3-methylether (mestranol) for an average of 16 months. During treatment a definite, but not significant, increase in protein-bound iodine (PBI) was found. In 11 normal fertile women, the thyroid function was evaluated before, during, and after cyclical treatment with megestrol acetate + mestranol. The observation period was 4 to 19 months. The thyroidal 4-hour uptake and 24-hour uptake of 131I and the uptake of 131I-triiodothyronine (T3) by erythrocytes and resin (Triosorb*) were determined at short intervals. No significant changes were observed in the two first mentioned tests, but it was characteristic of all patients except one, that the red-cell uptake of T3 was significantly decreased to values below the lower limit of normal, within 1 to 2 months of the commencement of treatment, and that it then remained unchanged during the remainder of the treatment period. One month after treatment was discontinued, all patients except two showed values within normal limits. The uptake of T3 by resin showed similar patterns during the treatment period, but one month after the medication was withdrawn, only 2 out of the 9 patients had values within the normal range. In 5 menopausal women, the thyroid function was evaluated before, during, and after continuous treatment with megestrol acetate by means of the same parameters as in the former group of patients. The observation period was 4 to 6 months. No significant changes were observed in the 4 indices of the thyroid function during and following treatment with megestrol acetate alone. It is therefore concluded that the significant decrease in the red-cell uptake and resin uptake of T3 observed during treatment will megestrol acetate + mestranol is caused exclusively by the oestrogen in this combination.