A randomized cross-over comparison of two low-dose oral contraceptives upon hormonal and metabolic parameters: I. Effects upon sexual hormone levels.

The effect of a low-dose triphasic oral contraceptive (OC) containing ethinyl estradiol and levonorgestrel (EE/NG) upon serum levels of endogenous sexual hormones was compared to that of a preparation containing EE and desogestrel (EE/DG). Blood samples were taken on Day 6, 11, 21, and 28 of a control cycle and of the third cycle of treatment with either the EE/NG or EE/DG preparation (11 volunteers each). After a washout period of 3 months, the contraceptives were changed in a cross-over fashion. Blood samples were again taken on Day 6, 11, 21, and 28 of the third washout cycle and the third treatment cycle. There was no significant suppression of serum LH and FSH during treatment with EE/NG and EE/DG except on Day 21, while estradiol levels were significantly lowered. Similar to the gonadotropin concentrations, the estrogen levels showed great individual variations; although they were depressed in the majority of the women, there was a considerable stimulation of follicular activity in 36% of the women under EE/NG and 18% under EE/DG. Both EE/NG and EE/DG suppressed significantly serum progesterone, testosterone, and DHEA-S, while prolactin was unaffected. In three cases an escape ovulation seemed to have occurred, but no pregnancy was observed. The spottings (8/22 women) and breakthrough bleedings (6/22 women) did not correlate with the serum levels of estradiol. The results indicate that the suppression of gonadotropin secretion during treatment with low-dose OC is a time-dependent process which in some women may be at or below the threshold of safe ovulation inhibition.