Emergency contraception
Emergency contraception prevents pregnancy after unprotected or inadequately protected intercourse using oral levonorgestrel, oral ulipristal acetate, or placement of a copper intrauterine device. Levonorgestrel 1.5 mg works best within 72 hours and loses effectiveness above a body mass index of 26, favoring ulipristal acetate 30 mg or the copper intrauterine device for later presentation or higher weight.
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What this article covers
- Overview
Definition: Emergency contraception is the use of a medication or device after unprotected or inadequately protected intercourse to prevent an unintended pregnancy, not to end one that has already implanted.
- Epidemiology
Who needs it: Any person of reproductive age after unprotected intercourse, a barrier method failure, a missed or delayed hormonal contraceptive dose, or sexual assault.
- Risk factors
Barrier method failure: A broken, slipped, or omitted condom is the most common trigger for a same-day request.
- Pathophysiology
Levonorgestrel: A progestin acting as a progesterone receptor agonist that delays or blocks the luteinizing hormone surge, postponing ovulation; it has no effect once ovulation has already occurred.
- Clinical features
Timing since intercourse: The single most important history item, since it decides which methods remain appropriate: levonorgestrel is labeled for the first 72 hours, while ulipristal acetate and the copper IUD extend to 120 hours.
- Differential diagnosis
Copper intrauterine device: The most effective option, up to 99% within 120 hours, but requires a clinic visit and pelvic exam, unlike either oral agent.
- Diagnosis
Eligibility is established by timing and body weight: Within 72 hours with a BMI of 26 or less, either oral agent is appropriate; beyond 72 hours, or with a BMI over 26, ulipristal acetate or the…
- Management
First, offer emergency contraception within the eligible window, regardless of exam findings: no exam or pregnancy test is required to dispense either oral agent.
- Complications
Nausea and vomiting: The most common side effect of either oral agent, related to the hormone dose; vomiting soon after the dose is the main reason a repeat dose or a switch to the copper IUD may be needed.
- Prognosis
Overall effectiveness: The copper IUD cuts pregnancy risk by up to 99% within 120 hours; both oral agents are effective but less protective, decline further the longer dosing is delayed, and do not substitute for a regular ongoing method.
- Prevention
Start or resume a regular method at the same visit: Every emergency contraception encounter should end with a plan for ongoing contraception, ideally started the same day rather than deferred.
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