Fertility: Timing of Conception with Multiple Partners

What time period has the highest likelihood of conception when having relations with different males?

Hello, doctor: A friend of mine had her menstrual period from August 27 to September 3.
Her menstrual cycle is irregular but usually around the early thirties.
She had sexual relations with her boyfriend on September 10, 11, 12, 13, and 14.
However, she had intercourse with another guy on September 17 and later found out she was pregnant.
Could you please advise when the likelihood of conception was highest? (During that month, she only had intercourse with the other guy on September 17; the rest were with her boyfriend.)

Jiaqi, 20~29 year old female. Ask Date: 2015/11/13

Dr. Lin Wenbin reply Obstetrics and Gynecology

You should consult a physician for genetic testing.
This is not a matter of probability.

Reply Date: 2015/11/13

More Info

Understanding fertility and the timing of conception can be quite complex, especially for individuals with irregular menstrual cycles. In your friend's case, we need to consider her menstrual cycle, the timing of ovulation, and the potential for sperm viability.

Typically, ovulation occurs about 14 days before the start of the next menstrual period. If your friend’s last menstrual period started on August 27 and her cycles are generally around 30 days, she would likely ovulate around September 10. This is a rough estimate, as individual cycles can vary significantly. Given that she had sexual intercourse with her boyfriend from September 10 to 14, it is possible that she could have conceived during this time, especially if she ovulated on or around September 10.

However, she also had sexual intercourse with another partner on September 17. Sperm can live inside the female reproductive tract for up to five days, so if she ovulated shortly after September 10, it is plausible that sperm from either partner could have fertilized the egg. If she ovulated later than expected, the intercourse on September 17 could also lead to conception.

To summarize, the highest probability of conception would likely be from the sexual encounters that occurred around the time of ovulation, which in this case would be between September 10 and 14. However, since she had intercourse with another partner on September 17, it is also possible that conception could have occurred from that encounter if ovulation happened later than anticipated.

In cases of irregular menstrual cycles, predicting ovulation can be challenging. Women may benefit from tracking their cycles using methods such as basal body temperature monitoring, ovulation predictor kits, or observing changes in cervical mucus to better understand their fertile windows.

It's also important to note that if your friend is unsure about the paternity of the child, a paternity test can be conducted after the baby is born to clarify the biological father.
In conclusion, while the most likely time for conception in your friend's case would be around September 10 to 14, the possibility of conception from the encounter on September 17 cannot be ruled out. If she is seeking to understand her fertility better or has concerns about her menstrual cycle, consulting with a healthcare provider or a fertility specialist would be beneficial. They can provide personalized advice and possibly recommend further testing or monitoring to help manage her reproductive health.

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