Plasma concentrations of endogenous hormones during one regular treatment cycle with a low-dose oral contraceptive and during two cycles with deliberate omission of two tablets.

In this open, prospective, phase-I study we closely monitored levels of endogenous progesterone, 17beta-estradiol, luteinizing hormone (LH) and follicle stimulating hormone in six healthy women. We determined plasma concentrations every 1-3 days during one untreated baseline cycle and during the first treatment cycle with regular pill intake of an oral contraceptive containing 30 microg ethinylestradiol plus 75 microg gestodene. During the following two treatment cycles, two tablets were deliberately omitted (in cycle 2 on days 6/7 and in cycle 3 on days 11/12). All but possibly one volunteer ovulated in the untreated pre-cycle, as concluded from LH peaks followed by marked increases of progesterone. During the regular first treatment cycle and even after deliberate omission of two tables in treatment cycles 2 and 3, the progesterone and estradiol levels remained low, so that we concluded that no ovulation took place. However, two volunteers showed some sort of LH peak in the first regular treatment cycle and all women showed LH increases of > 40 microg/ml in at least one omission cycle. In ten out of 12 cycles, omissions of pill intake were followed by an episode of intermenstrual bleeding. In conclusion, we have shown that, after omission of two consecutive oral contraceptive tables, the endogenous hormone parameters did not provide evidence for ovulation. Although this provides confirmation of the robustness of this oral contraceptive towards non-compliance, the widely published practical recommendations should be followed.