Contraception
Effectiveness and selection
Candidates must rank methods by typical-use failure rates and match them to patient-specific contraindications using the U.S. Medical Eligibility Criteria (US MEC, categories 1–4). Long-acting reversible methods-etonogestrel implant and copper or levonorgestrel IUDs-have failure rates below 1% and should be offered first-line to all patients, including nulliparous adolescents. Combined hormonal contraceptives (CHC) carry higher typical-use failure and estrogen-specific risks: VTE, arterial thrombosis, hypertension, and migraine with aura. Progestin-only pills, DMPA, implants, and IUDs avoid estrogen risk, but DMPA delays return to fertility and may reduce bone mineral density.
Practical prescribing
Quick-start any method when pregnancy can reasonably be excluded; provide emergency contraception if unprotected intercourse occurred within 5 days, and use backup for 7 days with CHC and 2 days with progestin-only pills. A copper IUD is the most effective emergency contraceptive, followed by ulipristal acetate (120 hours) and levonorgestrel (72 hours); both oral options lose efficacy with higher body weight. Postpartum CHC should be avoided for 21 days, and longer with additional VTE risk factors; progestin-only methods and IUDs can be started immediately. Postabortion, all methods may be initiated at the time of the procedure.
Traps include assuming antibiotics (other than rifampin/rifabutin) reduce contraceptive efficacy, withholding IUDs for nulliparity or prior ectopic pregnancy, and missing enzyme-inducing drugs (carbamazepine, phenytoin, topiramate, St. John’s wort, some antiretrovirals) that reduce hormonal pill, patch, ring, and implant efficacy but not IUDs.
Rule of thumb: if pregnancy status is uncertain, quick-start with a method plus emergency contraception and backup, and obtain a pregnancy test in 2–4 weeks.