Effect of varying amounts of ethinyl oestradiol in the combined oral contraceptive on plasma sex hormone binding globulin capacity in normal women.

The plasma sex hormone binding globulin (SHBG) capacity has been measured in 52 normal women, 11 women on various oral contraceptives containing 50 micrograms of ethinyl oestradiol and 11 women on oral contraceptives containing less than 35 micrograms of ethinyl oestradiol. The results show that women on oral contraceptives containing 50 micrograms of ethinyl oestradiol have a significantly raised SHBG capacity (p less than 0.005) whereas those patients on oral contraceptives containing 35 micrograms or less of ethinyl oestradiol have SHBG capacities which do not differ significantly from normal ovulating women (p greater than 0.05). Thus the 35 micrograms pill interferes less with bound/unbound sex steroid ratios than does the 50 micrograms pill.