What is the mechanism of action of combined estrogen-progestin oral contraceptives?

What is the mechanism of action of combined estrogen-progestin oral contraceptives?

• A. Stimulate ovulation
• B. Inhibit mid-cycle LH surge and thickens cervical mucus and thins endometrium
• C. Cause endometrial thickening
• D. Inhibit FSH completely

Answer: (B)

Combined estrogen-progestin pills work mainly by feedback on the hypothalamic-pituitary axis to prevent ovulation, which includes blocking the mid-cycle LH surge. The progestin also thickens cervical mucus, making it harder for sperm to reach the uterus, and it causes endometrial changes that make implantation unlikely. The estrogen component helps suppress follicular development by reducing FSH, but the key clinically observable effects are the suppression of the LH surge and the cervical mucus/ endometrial changes. Hence, the mechanism described—inhibiting the LH surge and thickening cervical mucus while thinning the endometrium—is the best match.

Combined estrogen-progestin pills work mainly by feedback on the hypothalamic-pituitary axis to prevent ovulation, which includes blocking the mid-cycle LH surge. The progestin also thickens cervical mucus, making it harder for sperm to reach the uterus, and it causes endometrial changes that make implantation unlikely. The estrogen component helps suppress follicular development by reducing FSH, but the key clinically observable effects are the suppression of the LH surge and the cervical mucus/ endometrial changes. Hence, the mechanism described—inhibiting the LH surge and thickening cervical mucus while thinning the endometrium—is the best match.