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Explain how progesterone-based contraceptives affect the menstrual cycle
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Correct answer:
The FSH rise at the beginning of a menstrual cycle is dependent on a decrease in the level of circulating progesterone in the female body. If serum progesterone levels remain high due to the use of progestin-containing contraception, the predicted rise in FSH will not occur upon demise of the corpus luteum. If this happens, follicular growth and selection of the dominant follicle will be inhibited in the next cycle and follicular phase estrogen levels will remain suboptimal throughout the follicular phase. As prolonged exposure to high estrogen levels is required for the LH surge, there will be no midcycle LH surge and ovulation will be suppressed. The trend toward lowering exogenous hormone exposures in all hormone-containing contraceptive methods has resulted in incomplete and unpredictable ovulation inhibition with most modern methods. True contraceptive efficacy for these approaches is more closely linked to progestin-mediated inhibition of sperm transport through the cervix (thickened mucous) and abnormalities in endometrial maturation.
