Mechanism of action of a 0.075 mg norgestrel progestogen-only pill 2. Effect on cervical mucus and theoretical risk of conception

The effect of deliberate non-adherence to a norgestrel progestin-only pill: A randomized, crossover study

“…We compared outcomes from the two cycles of deliberate misuse of norgestrel 0.075 mg with data from the baseline cycle of correct use, [6,7] and include data from this cycle in Appendix C. During correct use, 12 participants (24%) ovulated with a normal luteal phase. Similar proportions of normal ovulatory cycles occurred despite a delayed (22%) or missed pill (26%) (Appendix C).…”

“…However, the frequency of ultrasound and hormone evaluation increased to alternate days for three visits when we observed a follicle ≥15mm diameter; thus, progesterone concentrations are likely to reflect the quality of the luteal phase. Only four (8%), two (4%) and three (7%) women in the correct-use cycle [6], the delayed and missed pill cycles respectively had Hoogland score of 7, suggesting that even when ovulation was appeared normal it may not have been optimal for conception. [14] The conception protection algorithm likewise may have overestimated pregnancy risk given that any cervical mucus score above four in association with ovulation, normal or inadequate, was deemed to confer reduced contraceptive protection.…”

“…We assessed the theoretical conception risk based on the presence of potentially fertile mucus in the fertile window of an ovulatory cycle. We have previously reported the results from a baseline cycle of correct daily use for cervical mucus characteristics [6] and ovarian activity status [7], included baseline demographics of the study population. Here we report the effects of a delayed or missed pill.…”

Mechanism of action of norgestrel 0.075 mg a progestogen-only pill. I. Effect on ovarian activity

“…Even when ovulation occurs, POPs also render cervical mucus hostile to the passage of sperm so that women are still protected from pregnancy. Data from the cervical mucus score collected during 28 days of use of norgestrel 0.075 mg in this study are presented in a separate paper [9] .…”

“…This aspect of the mode of action is often forgotten when providers consider the value of this safe, estrogen-free contraceptive. Norgestrel 0.075 mg also has profound effects on cervical mucus important for preventing pregnancy [9] . Together, the two modes of action make this an effective contraceptive with failure rates similar to those of the combined pill [21] .…”