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How accurate is the date from my scan?

I had my first scan yesterday and was told I'm 14 weeks 1 day pregnant. I was confident I was 11 weeks and 3 days. The dates are quite crucial, if I'm 14 weeks, it's my ex's! How accurate is the dating?

8 Replies

It's operator dependant but fairly reliable. However I would never be happy assuming paternity on a scan, but you need to a DNA test.


Thank you. I see some very awkward conversations ahead!


As previous comment..

But also, my 6 week scan was wrong by a week in my opinion and was told that's impossible, I was sure as i knew exactly when my ovulation was... At my 12 week scan it turned out the earlier scan HAD been wrong by a week.

However, for it to be wrong by 3 weeks at that stage I would say is impossible. 3 weeks is a long time and the baby at 11 weeks compared to 14 weeks is a LOT smaller.

But yes, you'd need a DNA test to be 100% sure.


Thank you. I'm going to spend some more quality time with a calendar, but I see this being a bit difficult!


You can measure oddly in scans but usually only up to 12 weeks I heard. Mind you I am 39 weeks and my baby is measuring 40+ weeks in some parts of body so all weird.

Think about your periods as well...

Can it really be one of two people's if it's a 3 weeks gap? You would have 'timed it perfectly' if so.

Check it out with period dates before you tell your current partner/ex partner.


I haven't had a scan yet so i'm not sure whether the date will change or no. At the minute the doctor is saying 5 weeks 5 days which is taken from the first day of my last period. As my partner was away for 2 weeks at that time i know i'm only 3 weeks and 2/3 days.


I have managed to establish that how many weeks pregnant you are is the date of conception plus 2 weeks. This accounts for the difference plus an acceptable margin of error, and explains why they counted from before I had sex! Would have been very helpful if this had been explained at the scan!


The midwife, gp, scan date etc are always calculated from the last period and never from the date of conception.


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