Paternity question !!!

[linny123445]

So If a girl had a period October 9th 2021 and had sex with “guy A” October 22-24 2021 then again November 5th 2021 and took a plan B the 6th of November. She started bleeding November 9th (which I don’t remember if it was like a full period) but I’m not sure even if a plan b could make you fertile after she bled 3 days after taking it but then she had sex with “guy B” November 15th-27th somewhere between there a couple times. she had a first ultra sound January 4th, 2022 and was 7 weeks and 5 days along (CRL was 1.43cm) She also had an ultra sound March 29th,2022 and was Exactly 20 weeks.

Do you think there’s any possibility it is “guy A” baby?
Does the ultra sound match up with a period for November 9th?

[AnnieBrooke]

When a doctor says someone is a certain number of weeks "pregnant," the count the doctor uses does not begin on the day of conception but on the first day of the woman's last period. The pregnancy time frame doctors use (and any medical person including the ultrasound tech and medical textbooks and nurses and everyone dealing with obstetrics) begins the count of pregnancy on the first day of the woman's last period, not on the day the doctor thinks she might have ovulated and conceived. This is for historic reasons --  ovulating and conception are hidden and produce no signal, but a period is a big, obvious signal. So in the days before ultrasounds, a woman would go to her doctor and say "I think I'm pregnant," and the doctor would say "When did your last period come?" and begin the count then. That counting method is still used. The pregnancy time period is counted out as 40 weeks from first day of last period to full-term birth, even though from conception to full-term birth is only 38 weeks. To get 40 weeks, they add two weeks at the front end of the count (technically before the woman actually was pregnant) and calibrate everything to the first day of the last period. Even ultrasounds use this kind of 40-week count.

This means, when the doctor said "7 weeks 5 days along" on January 4, he was saying the woman's last period was about 7 weeks 5 days ago and she conceived around 5 weeks 5 days ago, approximately November 25. This rules out the first guy whose last activity with the woman was November 5.

[linny123445]

If there was any possibly sperm on November 5th, would it make a difference in ultra sound reading ?

[AnnieBrooke]

No. Sperm only lives 4-6 days in the woman's reproductive tract. It would all have been dead and gone by the 10th or the 11th of November.

[AnnieBrooke]

If you are asking if a person got pregnant on November 5, would the ultrasound give a different number of weeks pregnant in an ultrasound done on January 4 than it did, yes, it would. It would have said the pregnancy was ten or eleven weeks along, not seven.