Residency · Residency · Obstetrics Gynecology
Emergency Contraception
Introduction
Emergency contraception (EC) refers to methods used after unprotected or inadequately protected sexual intercourse to prevent unintended pregnancy. EC is not intended for regular use but serves as a critical backup option. Multiple modalities are available, each with distinct mechanisms, efficacy windows, and clinical considerations. Timely access and patient education are essential components of reproductive healthcare.
Methods of Emergency Contraception
Copper Intrauterine Device
The copper IUD (Paragard) is the most effective form of emergency contraception, with a failure rate of less than 0.1%. It creates a sterile inflammatory reaction that is toxic to sperm and ova, inhibiting fertilization and potentially preventing implantation. It is effective when inserted within 5 days (120 hours) of unprotected intercourse and can also be inserted up to 5 days after the earliest estimated date of ovulation. A major advantage is that it provides ongoing contraception for up to 10 years after insertion. Eligibility follows the same US MEC criteria as for routine copper IUD insertion, and it requires a trained provider and clinic visit. Importantly, its efficacy is not affected by body weight or BMI.
Levonorgestrel Emergency Contraception
Levonorgestrel 1.5 mg (Plan B One-Step and generics) is taken as a single oral dose. It works by delaying or inhibiting ovulation through suppression of the LH surge. It does not prevent implantation or disrupt an established pregnancy. It reduces pregnancy risk by approximately 85% when taken within 72 hours. While FDA-approved for use within 72 hours, it can be offered up to 120 hours with diminished efficacy. It is available over the counter without age restriction in the United States. An important limitation is reduced efficacy in women with a BMI of 26 kg/m2 or greater. For women over 70 kg, ulipristal acetate or the copper IUD should be considered.
<image>Timeline diagram showing the efficacy window of emergency contraception methods (copper IUD, ulipristal acetate, and levonorgestrel) from 0 to 120 hours after unprotected intercourse, with declining efficacy curves for oral methods and sustained efficacy for the copper IUD</image>
Ulipristal Acetate
Ulipristal acetate 30 mg (ella) is a single oral dose that requires a prescription in the United States. It is a selective progesterone receptor modulator (SPRM) that delays or inhibits ovulation even after the LH surge has begun, making it more effective than levonorgestrel at delaying ovulation in the late follicular phase. It reduces pregnancy risk by approximately 85% when used within 120 hours and maintains consistent efficacy throughout the entire 5-day window, unlike levonorgestrel, which declines after 72 hours. It is more effective than levonorgestrel in women with a BMI of 26 to 35 kg/m2, though efficacy may be reduced with a BMI above 35. An important interaction exists with hormonal contraceptives: they reduce the efficacy of ulipristal, so initiation of hormonal contraception must be delayed for 5 days after ulipristal use, with barrier methods used in the interim. For breastfeeding women, milk should be pumped and discarded for 24 hours after administration.
Yuzpe Method
The Yuzpe method is a combined oral contraceptive regimen consisting of 100 mcg ethinyl estradiol plus 0.5 mg levonorgestrel, taken as two doses 12 hours apart. It reduces pregnancy risk by approximately 75%, making it significantly less effective than dedicated EC methods. Nausea occurs in 50% and vomiting in 20% of users; pre-treatment with an antiemetic such as ondansetron 8 mg or meclizine 50 mg is recommended. This method is primarily used when dedicated EC products are unavailable, and any COC can be used with appropriate dose calculation.
| Method | Efficacy | Time Window | BMI Effect | Access | Key Consideration |
|---|---|---|---|---|---|
| Copper IUD | >99% (failure <0.1%) | Up to 120 hours | None | Requires provider/visit | Also provides ongoing contraception (10 years) |
| Ulipristal acetate (ella) | ~85% | Up to 120 hours (consistent) | Reduced >35 kg/m² | Prescription only | Delay hormonal contraception 5 days after use |
| Levonorgestrel (Plan B) | ~85% | Up to 72 hours (declines after) | Reduced ≥26 kg/m² | OTC, no age restriction | Less effective in women >70 kg |
| Yuzpe (COC regimen) | ~75% | Up to 72 hours | Not well studied | Any COC available | High nausea rate; use antiemetic |
Mechanism Clarification
No EC method disrupts an established pregnancy. All methods primarily work by delaying or preventing ovulation. Levonorgestrel has no effect if administered after ovulation has occurred. Ulipristal acetate can delay ovulation even after LH surge onset but is ineffective after ovulation has been completed. The copper IUD may also have post-fertilization effects by altering the endometrial environment, though this mechanism remains debated. EC is not an abortifacient according to the medical definition of pregnancy beginning at implantation.
Clinical Assessment and Counseling
When to Offer EC
EC should be offered after unprotected intercourse without any contraceptive use, after contraceptive failure (condom breakage or slippage, 2 or more missed active pills for COCs, more than 3 hours late for traditional POPs, late DMPA injection beyond 15 weeks, dislodged IUD or patch, or early ring removal), and to all survivors of sexual assault as part of comprehensive care.
Pregnancy Exclusion
A pregnancy test is not required before providing EC but should be offered. EC will not harm an existing pregnancy. If the menstrual period is delayed by more than 1 week after EC use, a pregnancy test should be performed.
Follow-Up Contraception
Ongoing contraception should be initiated promptly using the Quick Start approach. Hormonal contraception can begin immediately after levonorgestrel EC but must be delayed 5 days after ulipristal acetate, with barrier methods used during the waiting period. The copper IUD can serve as both EC and ongoing LARC, and this dual benefit should be discussed with all eligible patients.
<image>Clinical algorithm for emergency contraception selection based on time since unprotected intercourse, patient BMI, desire for ongoing contraception, and access to clinical services, with decision points leading to copper IUD, ulipristal acetate, or levonorgestrel recommendations</image>
Special Populations
For adolescents, awareness of over-the-counter availability of levonorgestrel EC should be ensured, and no parental consent is required. Advance provision improves timely use without increasing risk-taking behavior. For obese patients, the copper IUD is the preferred method regardless of BMI, and ulipristal is preferred over levonorgestrel for oral EC in overweight and obese women. For breastfeeding women, levonorgestrel is preferred over ulipristal (which requires pump-and-discard for 24 hours), and the copper IUD is safe during lactation. There is no medical contraindication to repeated use of oral EC, though patients should be counseled about more effective ongoing methods.
Advance Provision
ACOG recommends providing advance prescriptions for EC, particularly ulipristal acetate, to improve timely access. Evidence demonstrates that advance provision increases timely use without reducing use of ongoing contraception or increasing rates of unprotected intercourse. Levonorgestrel EC is available without a prescription, while ulipristal requires a prescription. Cost and access remain barriers for many patients.
<image>Comparison table of emergency contraception methods showing levonorgestrel, ulipristal acetate, copper IUD, and Yuzpe regimen with columns for mechanism, efficacy, timing window, BMI impact, prescription requirements, and transition to ongoing contraception</image>
Clinical Pearls
The copper IUD is the most effective EC and should be offered as a first-line option, especially when the patient desires ongoing contraception.
Ulipristal acetate maintains efficacy throughout the full 120-hour window, unlike levonorgestrel, which declines significantly after 72 hours.
BMI affects oral EC efficacy. For women over 70 kg or with a BMI of 26 or greater, ulipristal or the copper IUD should be preferred over levonorgestrel.
Hormonal contraception must be delayed for 5 days after ulipristal acetate to avoid reducing its efficacy.
EC is not an abortifacient and will not disrupt an established pregnancy. Patient counseling should address this common misconception.
References
- ACOG Practice Bulletin No. 152. Emergency Contraception. Obstet Gynecol. 2015;126(3):e1-e11.
- Glasier AF, Cameron ST, Fine PM, et al. Ulipristal acetate versus levonorgestrel for emergency contraception: a randomised non-inferiority trial and meta-analysis. Lancet. 2010;375(9714):555-562.
- Turok DK, Gero A, Simmons RG, et al. Levonorgestrel vs. copper intrauterine device for emergency contraception. N Engl J Med. 2021;384(4):335-344.
- Cleland K, Zhu H, Goldstuck N, et al. The efficacy of intrauterine devices for emergency contraception: a systematic review of 35 years of experience. Hum Reprod. 2012;27(7):1994-2000.
