Menstrual Cycle Pathophysiology

Study Notes

The dominant follicle develops and synthesizes estradiol, progesterone, and androgen, which stops menstrual flow, thickens the endometrial lining, and produces thin, watery cervical mucus.
FSH regulates aromatase enzymes that induce conversion of androgens to estrogens in the follicle.
The pituitary releases a midcycle LH surge that stimulates the final stages of follicular maturation and ovulation.
Ovulation occurs 24–36 hours after the estradiol peak and 10–16 hours after the LH peak.
Conception is most successful when intercourse takes place from 2 days before ovulation to the day of ovulation.

After ovulation, the remaining luteinized follicles become the corpus luteum, which synthesizes androgen, estrogen, and progesterone.
If pregnancy occurs, human chorionic gonadotropin prevents regression of the corpus luteum and stimulates continued production of estrogen and progesterone.
If pregnancy does not occur, the corpus luteum degenerates, progesterone declines, and menstruation occurs.

The goal of treatment is the prevention of pregnancy from sexual intercourse, with additional benefits including prevention of sexually transmitted infections (STIs) and menstrual cycle regulation.

The fertility awareness-based method involves avoiding intercourse when contraception is likely to occur, but is associated with a relatively high pregnancy rate.
Diaphragms and cervical caps are effective barriers that should be used with spermicide and inserted up to 6 hours before intercourse.
They must be left in place for at least 6 hours after intercourse, but should not be left in place for more than 24 hours (diaphragm) or 48 hours (cervical cap) to reduce the risk of toxic shock syndrome (TSS).

External condoms (also known as male condoms) are made from latex, which is impermeable to viruses, or lamb intestine, which is not impermeable to viruses.
Water-soluble lubricants are preferred to prevent condom breakdown.
Condoms with spermicides are not recommended, as they provide no additional protection against pregnancy or STIs, and may increase vulnerability to HIV.

With perfect use, CHC efficacy is more than 99%, but with typical use, up to 7% of individuals will have unintended pregnancy.
Monophasic CHCs contain a constant amount of estrogen and progestin for 21 days, while biphasic and triphasic pills contain variable amounts of estrogen and progestin for 21 days.
Extended cycle pills and continuous combination regimens may reduce adverse effects and are more convenient.

Progestin-only “minipills” are less effective than CHCs and are associated with irregular and unpredictable menstrual bleeding.
They must be taken every day at approximately the same time of day to maintain efficacy and are associated with more ectopic pregnancies than other hormonal contraceptives.

Over 35 years of age, use of CHCs containing less than 50mcg estrogen may be considered in healthy nonsmoking individuals, but are not recommended for individuals with migraine, uncontrolled hypertension, smoking, or diabetes with vascular disease.
Smoking 15 or more cigarettes per day by individuals over 35 years is a contraindication to the use of CHCs, and progestin-only methods should be considered.

EC is used to prevent unintended pregnancy after unprotected or inadequately protected sexual intercourse.
FDA-approved progestin-only and progesterone receptor modulator products are recommended as first-line EC options.
Progestin-only EC formulations containing one 1.5 mg tablet of levonorgestrel are available without a prescription in the United States, but may be less effective in individuals weighing greater than 75 kg.