Pregnancy Chances After Unprotected Intercourse: A Guide - Obstetrics and Gynecology

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Understanding the chances of pregnancy after unprotected intercourse is a common concern for many couples. In your case, let's break down the timeline and analyze the factors involved.

Your girlfriend's last menstrual period (LMP) started on October 8, and she typically has a regular cycle of about 28 days. This means her next expected period would be around November 5. The ovulation period, which typically occurs about 14 days before the next expected period, would be around October 22. The "fertile window" usually spans a few days before and after ovulation, so in this case, it would likely be from October 18 to October 26.

You mentioned that unprotected intercourse occurred on the evening of October 28, which is just outside the typical fertile window. However, sperm can survive in the female reproductive tract for up to five days, so there is still a possibility, albeit lower, of sperm being viable if ovulation occurred later than expected.

After the intercourse, your girlfriend took an emergency contraceptive pill (ECP) on October 29. ECPs are most effective when taken as soon as possible after unprotected intercourse, ideally within 72 hours, but they can still be effective up to 120 hours (5 days) after. The effectiveness of ECPs decreases the longer you wait, but they can significantly reduce the chances of pregnancy if taken promptly.

Regarding the symptoms your girlfriend experienced, such as the feeling of discomfort in her lower abdomen on November 4, this could be due to a variety of reasons. It might be related to hormonal changes, the effects of the emergency contraceptive pill, or even premenstrual symptoms. The absence of menstruation by November 6 could indicate a potential pregnancy, but it is also possible that the ECP has delayed her period.

To summarize, while the chances of pregnancy from the intercourse on October 28 are relatively low due to the timing in relation to ovulation and the prompt use of emergency contraception, it is not impossible. If your girlfriend's period does not arrive within a week of the expected date, it would be advisable for her to take a home pregnancy test for confirmation.
In addition, if there are any concerns or unusual symptoms, it is always best to consult with a healthcare provider for personalized advice and further evaluation. They can provide guidance on next steps, whether that involves a pregnancy test, discussing contraceptive options, or addressing any health concerns.
In conclusion, while the risk of pregnancy exists, the use of emergency contraception significantly reduces that risk, and monitoring her menstrual cycle will provide further clarity.