Aa
What are your best predictions for paternity here?
Before I start, yes, I know the only way to know anything for sure is to do a paternity test. But until then, educated guesses are the best we have.
Someone I know is pregnant. On March 25 her ultrasound dated her pregnancy at 13 weeks and 1 day. She last had sex with a guy on December 21st at the latest. She can't remember exactly when she stopped, but it was no later than the 21st.
Now, if her ultrasound was on target that gives her a conception date around January 6th. But as we know, 13 week ultrasounds can be off by 8 days at most. What do you think is the likelihood that this guy could be the father?
I'm asking here because I'm assuming you guys are well versed in how accurate ultrasounds are and how long sperm live. It's always best to go worst case.
Again, we know only a paternity test is a guarantee, but what do you think?
Someone I know is pregnant. On March 25 her ultrasound dated her pregnancy at 13 weeks and 1 day. She last had sex with a guy on December 21st at the latest. She can't remember exactly when she stopped, but it was no later than the 21st.
Now, if her ultrasound was on target that gives her a conception date around January 6th. But as we know, 13 week ultrasounds can be off by 8 days at most. What do you think is the likelihood that this guy could be the father?
I'm asking here because I'm assuming you guys are well versed in how accurate ultrasounds are and how long sperm live. It's always best to go worst case.
Again, we know only a paternity test is a guarantee, but what do you think?
COMMUNITY LEADER
Many women who write in on this forum have had doctors say that by 12 weeks 0 days, the margin for error is +/- 7 days. Since the margin for error at 6 weeks 0 days is only about 1 day at most, it makes sense to add a day or even two by week 13, in order to err on the side of caution.
Frankly, as far as I know, dating conception by measuring with ultrasounds has never been strictly tested in double-bind peer-reviewed studies, certainly not enough to rule out other theories (one published paper even suggests an embryo can lie dormant without developing at all, and then begin to grow. I've never seen any study of dating pregnancy by embryonic measurement that attempts to screen out anything like that). In short, the rate of variance from average is not the hardest of hard science at this point. The numbers I use are all from reports of what women's doctors told them about the margin for error. (One gal's doctor even said an ultrasound could be 2 weeks off at 12 weeks. That one seemed too cautious even to me.)
In your shoes, I would suggest to your friend is that it is unlikely that the sex on December 21 produced the pregnancy. I assume she intends a DNA test once the baby is born to put the question to rest forever, but would counsel her to go through her pregnancy assuming the sex from December 21 is ruled out.
Frankly, as far as I know, dating conception by measuring with ultrasounds has never been strictly tested in double-bind peer-reviewed studies, certainly not enough to rule out other theories (one published paper even suggests an embryo can lie dormant without developing at all, and then begin to grow. I've never seen any study of dating pregnancy by embryonic measurement that attempts to screen out anything like that). In short, the rate of variance from average is not the hardest of hard science at this point. The numbers I use are all from reports of what women's doctors told them about the margin for error. (One gal's doctor even said an ultrasound could be 2 weeks off at 12 weeks. That one seemed too cautious even to me.)
In your shoes, I would suggest to your friend is that it is unlikely that the sex on December 21 produced the pregnancy. I assume she intends a DNA test once the baby is born to put the question to rest forever, but would counsel her to go through her pregnancy assuming the sex from December 21 is ruled out.
The due date was given to her on the same day as the ultrasound, March 25.
Where did you hear a 13 week ultrasound has a margin of error of 8 or 9 days? I've heard 8 days at most, but they usually say 3-5 days, but very often no more than 7. I've certainly never heard as much as 9.
Where did you hear a 13 week ultrasound has a margin of error of 8 or 9 days? I've heard 8 days at most, but they usually say 3-5 days, but very often no more than 7. I've certainly never heard as much as 9.
COMMUNITY LEADER
And the due date was given to her in that thirteenth-week ultrasound? If it was, given a margin for error of +/- 8 or 9 days takes you to around December 28.
If the due date of September 29 was not given to her in her 13th week but was given to her later in the pregnancy, you will need to use a wider margin for error.
It would be unusual or impossible for sex on December 21 to have produced a pregnancy on December 28, but it is a pretty slim margin given the 5- to 6-day life of sperm in a woman's reproductive tract.
If the due date of September 29 was not given to her in her 13th week but was given to her later in the pregnancy, you will need to use a wider margin for error.
It would be unusual or impossible for sex on December 21 to have produced a pregnancy on December 28, but it is a pretty slim margin given the 5- to 6-day life of sperm in a woman's reproductive tract.
Sorry, original was correct. She only had sex with 1 guy past the 21st of December. I got confused.
No, she was having sex with 2 guys past the 21st. One she stopped much earlier than that.
These posts could do with an edit button!
These posts could do with an edit button!
Sorry, sent my other reply before I was ready and can't see where to edit it.
Yes, she was having sex with someone else around the New Year. She had sex with three guys in December, but only 1 past the 21st.
I just used a conception calculator online that works by putting in the due date she was given. Of course, she could have conceived at any time around the 6th, not the 6th specifically. And as I said, ultrasounds can be off by up to a week.
Yes, she was having sex with someone else around the New Year. She had sex with three guys in December, but only 1 past the 21st.
I just used a conception calculator online that works by putting in the due date she was given. Of course, she could have conceived at any time around the 6th, not the 6th specifically. And as I said, ultrasounds can be off by up to a week.
COMMUNITY LEADER
Did the March 25 ultrasound give her a due date? Was she having sex with someone around January 6, when you have determined that her conception date was?
Have an Answer?
You are reading content posted in the DNA / Paternity Community
Get information and tips on how to help you choose the right place to deliver your baby.
Get the facts on how twins and multiples are formed and your chance of carrying more than one baby at a time.
Learn about the risks and benefits of circumcision.
What to expect during the first hours after delivery.
Learn about early screening and test options for your pregnancy.
Learn about testing and treatment for GBS bacterium.
