Some highlights from my contraception mythbusting crusade. If only I could get to the Supreme Court…
For combined Estrogen and Progesterone contraceptives: These prevent ovulation, primarily with the progesterone. The normal menstrual cycle is below, the cyclic fall and rise of progesterone triggers the LH surge. By keeping this high, negative feedback to the hypothalamus is washed out. No LH surge, no ovulation. The estrogen is there to recruit more progesterone receptors (so less progesterone is needed), and stabilize the endometrium (less breakthrough bleeding).
Large doses of progesterone only contraceptives (DepoProvera, the MiniPill, and Implants) is enough progesterone to prevent ovulation. The lower dose progesterone only contraceptives (Mirena/Skyla IUDs, the MiniPill) work by thickening cervical mucus, reduce fallopian tube motility, and thinning the endometrium.
IUDs are not abortifacients. They actually prevent conception from ever happening: the IUD creates a sterile inflammatory response that is toxic to sperm and ova. This has been shown in vivo with tubal flushing studies. Women who are not on contraception can be found to have sperm, non fertilized eggs, and even fertilized, but nonviable eggs in the tubes. Women with IUDs have fewer of all three: the sperm never get there and fertilization doesn’t happen.
IUDs do not increase the risk of STIs or PID. There is a slightly higher risk of infection in the first 20 days after insertion. This is either from incompletely sterile technique or if the woman is already infected when the IUD is placed. So make sure your patient is free from cervicitis before inserting an IUD. After that, the risk is no different. This myth comes from an old IUD, the Dalkon Shield (that parasite-looking thing in the picture below), which DID increase the risk of PID, because it had a multifilament string that acted as a bacterial superhighway.
Emergency Contraception is not an abortifacient either. The EC pills are mostly large doses of progesterone- which works to prevent ovulation, thicken cervical mucus, and impair motility in the fallopian tubes. Women do not get pregnant if they have had intercourse after ovulation. Sperm lives in the female reproductive tract for up to 6 days after intercourse, and all that time it is making its way up to the fallopian tubes, where fertilization happens. EC pills prevent ovulation, and are more effective the sooner after unprotected intercourse they are taken (this is why it is helpful for a woman to have it at home before something goes wrong). If a woman does get pregnant despite taking EC, the pills will not harm the pregnancy.
Here’s a great table to use when talking about contraception with your patients. Aim to pick a method from the top row: these are the most effective with typical use (because they don’t require the woman to think about anything once in place). As you move down the rows, preventing pregnancy gets closer and closer to just luck. And we can do better than that!