Emergency Contraception: Its Effectiveness After Unprotected Sex - Obstetrics and Gynecology

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Emergency contraception (EC) is a critical option for individuals who have had unprotected sex or contraceptive failure, such as a broken condom or missed birth control pill. In your case, you mentioned having unprotected intercourse on November 26 and 27, with ejaculation occurring inside. You also indicated that you took emergency contraception afterward.
The effectiveness of emergency contraception, particularly ulipristal acetate (Ella), is quite significant when taken within a specific timeframe after unprotected intercourse. Ella can be effective up to 120 hours (5 days) after unprotected sex, with its efficacy being highest when taken as soon as possible. Research indicates that when taken within 72 hours, ulipristal acetate can reduce the risk of pregnancy by approximately 97%. However, its effectiveness diminishes the longer you wait to take it after the unprotected intercourse.

Given that you took the emergency contraceptive after the unprotected sex, it is important to consider a few factors:
1. Timing of Administration: If you took Ella within 120 hours after the last instance of unprotected sex, it should still provide a significant level of protection against pregnancy. The sooner you take it after the event, the better the chances of preventing ovulation or fertilization.

2. Ovulation Timing: If your girlfriend was close to her ovulation period during the time of intercourse, the risk of pregnancy could be higher. Ovulation typically occurs about 14 days before the start of the next menstrual period, but this can vary based on individual cycles. If she was ovulating during the time of intercourse, the effectiveness of the emergency contraceptive may be slightly reduced, but it still works primarily by delaying ovulation.

3. Mechanism of Action: Emergency contraceptives like Ella primarily work by preventing or delaying ovulation. They may also alter the uterine lining to prevent implantation, but this is not their primary mechanism. If ovulation has already occurred and fertilization has taken place, the effectiveness of EC may be limited.

4. Side Effects and Menstrual Changes: After taking emergency contraception, it is common for women to experience changes in their menstrual cycle. This can include a delay in the onset of the next period, which can be a source of anxiety. If your girlfriend's period is delayed by more than a week, it is advisable for her to take a pregnancy test to confirm whether or not she is pregnant.

5. Follow-Up: If there are any concerns about potential pregnancy or if your girlfriend experiences unusual symptoms, it is essential to consult a healthcare provider. They can provide further guidance and support, including options for regular contraception moving forward.

In summary, while the risk of pregnancy exists after unprotected sex, taking emergency contraception like Ella significantly reduces that risk, especially when taken promptly. If your girlfriend experiences a delay in her menstrual cycle after taking the pill, it is advisable to take a pregnancy test to rule out pregnancy. Always consult with a healthcare professional for personalized advice and to discuss ongoing contraceptive options.