How Effective is Emergency Contraception After 55 Hours? - Obstetrics and Gynecology

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Emergency contraception (EC) is a critical option for individuals who have had unprotected intercourse or contraceptive failure. The effectiveness of EC, particularly medications like Ella (Ulipristal Acetate), varies depending on the timing of administration after unprotected intercourse.
Ella is designed to be taken within 120 hours (5 days) after unprotected sex, and it is most effective when taken as soon as possible. Research indicates that when taken within 24 hours, Ella can reduce the risk of pregnancy by up to 98%. However, as time progresses, the effectiveness diminishes. After 48 hours, the effectiveness is still significant, but it may drop to around 90% or lower by the 72-hour mark. By the time you reach 55 hours post-intercourse, while Ella is still effective, the probability of preventing pregnancy is not as high as it would be if taken earlier.

In your specific case, taking Ella 55 hours after unprotected intercourse means you are still within the window of effectiveness, but the exact probability of preventing pregnancy can vary based on several factors, including your menstrual cycle timing, the timing of ovulation, and individual physiological responses to the medication.
It's also important to note that Ella works primarily by delaying or inhibiting ovulation. If ovulation has already occurred, the effectiveness of the medication may be reduced. Therefore, if you are close to your ovulation window, the chances of preventing pregnancy may be lower.
In terms of statistics, studies suggest that the effectiveness of Ella decreases as time passes after unprotected intercourse. While specific data for the 55-hour mark may not be readily available, it is reasonable to estimate that the effectiveness is still significant, but not as high as it would be if taken within the first 24 hours.
If you have concerns about potential pregnancy after taking Ella, it is advisable to monitor your menstrual cycle closely. If your period is delayed by more than a week, consider taking a pregnancy test or consulting a healthcare provider for further evaluation.
In summary, while taking Ella 55 hours after unprotected intercourse still provides a chance of preventing pregnancy, it is essential to understand that the effectiveness is not guaranteed and decreases over time. For future reference, using regular contraceptive methods or taking emergency contraception as soon as possible after unprotected intercourse can significantly enhance the chances of preventing unintended pregnancy.