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Due date from 12 weeks shows 22nd december when was conception
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134578 tn?1614729226
By your 12th week, a doctor using an ultrasound for measurement will give a range rather than a single day. This is because some babies grow faster and some grow slower than average.  In your case, March 31 plus or minus 7 days would be the estimated conception date. How precise of a conception date are you needing? Are you trying to rule out someone?
And, did you have an ultrasound? Was it your first one or was there one that was earlier than 12 weeks?
Had an ultrasound may 14 meassuring 7w6d
When they did the ultrasound on May 14, what due date did they give you from that ultrasound?
They didnt just at 12 week scan
Did they give you a photograph of the earlier scan? Sometimes it says "EDD" and a date on it along the edge.
Was your earlier ultrasound at your doctor's, or at one of those walk-in places that offer free scans so women won't get abortions? If it was at your doctor's, it sounds like the earlier ultrasound would suggest conception around two days later than March 31 (still within the range I mentioned above). When was the sex you are trying to rule out?
Just cant remember if my cycle in march was normal but my lmp in feb was the 10th and if i had conceived beginning of march
Beginning of March is not an issue. Even given an allowance for the lateness of the ultrasound, your data says  conception was no earlier than the 25th of March at the earliest, and your info from your first ultrasound (if it's reliable) pretty much rules out that it could even be that early. Not the beginning of March in any case.
So i couldnt of concieved at the beggining of march is what your saying
If your first ultrasound was done at a hospital or your doctor's office, it's reliable. If it was done at a place where they do them for the reason of convincing girls to not get abortions, it's possible it is less reliable but probably still pretty close. That seventh-week ultrasound and your 12th week ultrasound point to conception being at the END of March (or even early April), not to the beginning of March. It sounds like you have zero chance that the dad is from sex at the beginning of March.
So you just count back 266days from your due date i always thought ultrasound was calculated from conception thanks annie
Yes, ultrasounds are calibrated to use the same GA count as all medical professionals use. Doctors, nurses, ultrasound techs, ultrasound machines, medical textbooks, etc  all mean the same thing when they say "weeks pregnant," they use a gestational-age count that begins on the first day of the woman's last period. About 2 weeks into that GA time period would be ovulation and conception, so, although day 1 of your last period to full-term birth is 280 days, to count back to conception, you only count 266 days because you ovulate a couple of weeks later than the first day of your last period.
So counting back takes me to the 17th march is that when they would of thought my lmp was? Then conceived 2 weeks after that date sex from end of feb would mean id be due in november with conception beginning of march correct?
Counting back takes you to the 17th of March, yes, and if your cycles always come perfectly every 28 days, the doctor would assume that March 17 was the first day of your last period. But women's periods don't always come every 28 days like clockwork, so if yours didn't, the doc will still use March 17 as the start point because of what size your baby was at 12 weeks.

In short, the measurements of the actual embryo seen on an ultrasound are way more important than when your last period came. Once you get an ultrasound, that data rules. The ultrasound saw and measured and was able to extrapolate from the measurements and developmental markers when the baby began life. Then it counted back two weeks before that and assigned a start point for the pregnancy time period of March 17, and gave you the estimated due date based on that. It also assumed that two weeks after that point, or March 31, is when the baby was conceived and began to develop. This is why I said above that your ultrasounds show that conception was in the END of March not the end of February. With those ultrasound results, sex at the end of Feb. would not have produced that pregnancy.

If you got pregnant at the end of February, your due date would be a month earlier than it is, and besides, the baby would not have looked the way it did in your early ultrasounds.
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