Pregnancy Timing: When Did Conception Likely Occur?

Pregnancy Test Timing Issues

Hello Doctor, I would like to ask you a question.
My last menstrual period was from February 24 to 26.
I had sexual intercourse on March 9 and March 19.
After the intercourse on March 19, I took emergency contraception.
However, on March 29, I tested positive for pregnancy with a morning urine test.
Which instance of sexual intercourse is more likely to have caused the pregnancy? Thank you.

Bi Bi, 20~29 year old female. Ask Date: 2023/03/31

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, it might be from the event on March 9th.
Wishing you good health.

Reply Date: 2023/03/31

More Info

To determine the likely timing of conception in your case, we need to consider the menstrual cycle and the timing of ovulation. The average menstrual cycle is about 28 days, but it can vary significantly among individuals. Ovulation typically occurs around 14 days after the first day of your last menstrual period (LMP). In your case, your last menstrual period started on February 24 and ended on February 26. Assuming a typical 28-day cycle, ovulation would likely have occurred around March 10.

Given that you had sexual intercourse on March 9 and March 19, it is important to note that sperm can survive in the female reproductive tract for up to five days. Therefore, intercourse on March 9 could potentially lead to conception if ovulation occurred shortly after. However, the intercourse on March 19, which was just a few days before you took the morning-after pill, is also a critical factor to consider.

The morning-after pill is most effective when taken as soon as possible after unprotected intercourse. Since you took the pill after the March 19 encounter, it would have significantly reduced the likelihood of pregnancy from that act. However, if you had already conceived from the March 9 encounter, the pill would not affect that pregnancy.

Considering the timing, it is most likely that conception occurred from the sexual encounter on March 9. The positive pregnancy test on March 29, which is about 10 days after the likely ovulation date, aligns with the timing of conception from that earlier encounter.

In summary, while both sexual encounters were close to the ovulation window, the evidence suggests that the encounter on March 9 is the most likely cause of the pregnancy. It is also important to remember that individual variations in cycle length and ovulation timing can affect these conclusions. If you have further concerns or questions about your pregnancy, it would be advisable to consult with a healthcare provider for personalized advice and care.

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