A 26-year-old woman, gravida 1 para 1, comes to the office for a contraception counseling visit. The patient has been using a progestin-only pill for contraception since giving birth a year ago. She would like to switch to a combined hormonal contraceptive as she is no longer breastfeeding. The patient has no chronic medical conditions and takes no other daily medications. Vital signs and physical examination are unremarkable. Which of the following is the primary mechanism of pregnancy prevention when the patient switches to a combined hormonal contraceptive?

Question

A 26-year-old woman, gravida 1 para 1, comes to the office for a contraception counseling visit.  The patient has been using a progestin-only pill for contraception since giving birth a year ago.  She would like to switch to a combined hormonal contraceptive as she is no longer breastfeeding.  The patient has no chronic medical conditions and takes no other daily medications.  Vital signs and physical examination are unremarkable.  Which of the following is the primary mechanism of pregnancy prevention when the patient switches to a combined hormonal contraceptive?

Quizplus · Accepted Answer

11ec160b_3bc7_2238_9249_f53efe766795_MD0001_00 Both the estrogen and progestin components in combined hormonal contraceptives (CHCs) are effective at preventing pregnancy, and when used together, have additive effects. CHCs provide an exogenous source of estrogen and progestin, which result in constant elevated systemic levels of both hormones. The elevated serum estrogen and progestin levels exert negative feedback on both the hypothalamus (decreases gonadotropin-releasing hormone [GnRH] pulsatile release) and the anterior pituitary (decreases gonadotropin [LH, FSH] release). The estrogen component provides the most important mechanism of pregnancy prevention because it specifically prevents the release of FSH, which suppresses folliculogenesis. Without a dominant follicle and a mid-cycle LH surge, ovulation is inhibited, and pregnancy is prevented. The progestin component not only works in conjunction with estrogen to prevent the gonadotropin release but also provides pregnancy prevention via additional mechanisms. Progestin increases cervical mucus viscosity (which prevents sperm passage) and decreases Fallopian tube peristalsis and motility (which limits oocyte transport). Continuous progesterone exposure also induces endometrial changes that impair embryo implantation. However, the estrogen component of CHCs helps ensure that ovulation inhibition is the primary mechanism of pregnancy prevention (Choices C and E). (Choice B) The estrogen component of CHCs leads to an increase in sex hormone-binding globulin (SHBG), which can then bind additional free-circulating androgens (eg, testosterone). The increase in SHBG by the estrogen component of CHCs is why CHCs are effective at treating conditions associated with hyperandrogenism (eg, polycystic ovary syndrome) and mitigating their clinical features (eg, acne, hirsutism). (Choice D) The rise in the systemic levels of both estrogen and progesterone leads to a decrease (not increase) in the pulsatile activity of gonadotropin-releasing hormone through a negative feedback system. Educational objective: Combined hormonal contraceptives are effective at preventing pregnancy by decreasing the release of gonadotropins, which suppresses folliculogenesis and inhibits ovulation.

A 26-Year-Old Woman, Gravida 1 Para 1, Comes to the Office