Effectiveness of Emergency Contraceptive Pills After Unprotected Intercourse - Obstetrics and Gynecology

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Emergency contraceptive pills (ECPs), such as Levonorgestrel (commonly known as Plan B or "愉婷錠"), are designed to prevent pregnancy after unprotected intercourse or contraceptive failure. The effectiveness of these pills largely depends on how soon they are taken after the unprotected event.
In your case, since you had unprotected intercourse and are concerned about the possibility of pregnancy, taking the emergency contraceptive pill as soon as possible is a crucial step. ECPs are most effective when taken within 72 hours (3 days) after unprotected intercourse, but they can still be taken up to 5 days after the event, although their effectiveness decreases over time.
The mechanism of action for ECPs primarily involves delaying ovulation. If ovulation has already occurred, the pill may not be effective in preventing pregnancy. However, since you mentioned that the intercourse was recent, taking the ECP promptly increases your chances of preventing pregnancy significantly.

Regarding your concern about residual sperm from the intercourse, it is important to note that sperm can survive in the female reproductive tract for up to five days. Therefore, if ovulation occurs during this time, there is a risk of pregnancy. This is why taking the ECP as soon as possible is essential.

It is also worth mentioning that ECPs do not terminate an existing pregnancy; they work to prevent one from occurring. If you are already pregnant, taking ECPs will not affect the pregnancy.
In terms of side effects, some women may experience nausea, fatigue, headache, or changes in their menstrual cycle after taking ECPs. It is also common for the next menstrual period to be earlier or later than expected, or for the flow to be lighter or heavier than usual. If your period is more than a week late after taking the ECP, it is advisable to take a pregnancy test to confirm whether or not you are pregnant.

Lastly, while ECPs are a safe and effective option for preventing pregnancy after unprotected intercourse, they should not be used as a regular form of contraception. Regular contraceptive methods, such as birth control pills, condoms, or intrauterine devices (IUDs), are more effective for ongoing prevention of pregnancy.

In summary, taking the emergency contraceptive pill as soon as possible after unprotected intercourse is your best option to prevent pregnancy. If you have any further concerns or questions, it is always a good idea to consult with a healthcare professional for personalized advice and guidance.