Serum tsh and serum t3 levels during normal menstrual cycles and during cycles on oral contraceptives.

Serum TSH and serum T3 levels were studied in 35 normally menstruating women and in 35 women on oral contraceptives in order to find out whether the levels of TSH and T3 were related to the menstrual cycle or changed by oral contraceptives. Serum TSH AND T3 were found to be unchanged throughout the normal menstrual cycles and during the cycles of oral contraceptives. The TSH level was higher in the women on oral contraceptives than in the normally menstruating women. This might be due to a direct thyroid inhibitory effect of oestrogen. As could be expected the levels of T3 and T4 were higher in women on oral contraceptives than in normally menstruating women.