Pregnancy Risks After Unprotected Intercourse - Obstetrics and Gynecology

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When it comes to understanding pregnancy risks after unprotected intercourse, several factors need to be considered, including the timing of ovulation, the effectiveness of contraceptive methods, and individual physiological responses.

In your case, your girlfriend's menstrual cycle is typically around 28 days, with her last period starting on February 15. If we assume she has a regular cycle, ovulation would likely occur around day 14 of her cycle, which would be around February 29. Unprotected intercourse on March 2, which is just a few days after her ovulation window, does pose a risk for pregnancy, as sperm can survive in the female reproductive tract for up to five days. Therefore, if ovulation occurred on or around February 29, there is a possibility that sperm from intercourse on March 2 could fertilize an egg.

You mentioned that your girlfriend took emergency contraception (the "morning-after pill") on March 2. Emergency contraceptive pills (ECPs) are designed to prevent pregnancy after unprotected intercourse and are most effective when taken as soon as possible after the event. They work primarily by delaying ovulation, preventing fertilization, or preventing a fertilized egg from implanting in the uterus. However, ECPs are not 100% effective, and their efficacy decreases the longer you wait to take them after unprotected intercourse.

As for the symptoms your girlfriend is experiencing, such as breast tenderness (which you referred to as "脹奶的感覺"), this can be an early sign of pregnancy, but it can also be attributed to hormonal changes related to her menstrual cycle or the use of emergency contraception. It is not uncommon for women to experience breast tenderness before their period, especially if they are experiencing hormonal fluctuations.

Given that today is March 12, and her next expected period would be around March 15, it is advisable for her to take a home pregnancy test if her period does not arrive on time. Home pregnancy tests are generally reliable and can detect pregnancy as early as the first day of a missed period. If the test is positive, it would confirm pregnancy, and if negative but her period does not come, she should consult a healthcare provider for further evaluation.

In summary, while there is a risk of pregnancy due to the timing of intercourse relative to ovulation, the use of emergency contraception significantly reduces that risk. However, it is not foolproof. If your girlfriend is experiencing symptoms that are concerning or if her period is late, it is best for her to take a pregnancy test and consult with a healthcare provider for personalized advice and support.