Contraception basics for the USMLE CK exam

by / Monday, 31 May 2010 / Published in OB/GYN

Here are some contraception basics you will surely see on the CK exam.  There are not too many tricks thrown around with this topic, a general understanding can provide you with 2-3 easy points in this area.

Oral contraceptives that combine progestin and estrogen

  • Estrogen suppresses FSH, which prevents selection and maturation of a dominant follicle.
  • Progestin works by suppressing LH, which inhibits ovulation.  It also thickens cervical mucosa which further prevents the ability of semen to pass into the uterus.
  • Together, they inhibit pregnancy by thinning the endometrial lining and resulting in light or misses menses.

Phasic vs. Monophasic Pills:

  • Phasic pills vary the ratio of estrogen and progestin.  This decreases the dose of hormone given but it increases the risk of breakthrough bleeding
  • Monophasic pills deliver a constant dose of estrogen and progestin throughout the month

** Following cessation of OCP’s, fertilization usually resumes immediately.  A small percentage of users will experience a period of infertility, known as “postpill amenorrhea”

 Advantages and Disadvantages of OCP’s



  • Reliable with failure rate of <1%
  • Protective against ovarian and endometrial cancer
  • Decreases incidence of PID and ectopic pregnancies
  • Makes menses more predictable and less painful/lighter.
  • Must be taken daily close to the same time
  • No STD protection
  • Up to 30% breakthrough bleeding
  • May cause depression, weight gain, hypertension, acne, bloating, and weight gain


Alternatives to OCP’s

  • Progestin-only pills – “mini-pills”
  • Depo-Provera – IM injection lasts for 14 weeks
  • Norplant – subcutaneous implant lasts up to 5 years
  • Intrauterine device à device left in place for several years
  • Emergency Contraception à progestin/estrogen taken within 72hr 

This covers the basics you should know and understand when it comes to very basic concepts regarding contraception.

4 Responses to “Contraception basics for the USMLE CK exam”

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