NHS Dating Scan

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Dating scan in April had me at 13 weeks 6 days GA. 3 days difference to my LMP. Does an ultrasound measure from LMP? If so, is 3 days difference ok?

Dating scan is more accurate BUT also 3 days is kinda negligible, remember due dates are a bit of a myth and think more of a due 2 week period ☺️

dating scan more accurate as they will measure length of baby, LMP works when based off a perfect 28 day cycle with people ovulating exactly on day 14 but real life often doesn’t work this way. 3 days difference is of no concern ☺️

Thanks for your replying! So the dating scan is still measured from LMP? Sorry I’m so confused how this all works x

Thank you! But this still goes off lmp? X

No the LMP isn’t used for the dating scan that’s just an estimated date from before you can have an accurate dating scan due to the variabilities with people’s cycle length etc.

Your dating scan gives you your new due date OP. Forget LMP now.

Ah ok! So baby is measuring from when I conceived now? Sorry I’m still so confused. I’ve heard the 2 weeks pregnancy is actually 4 weeks.

Ignore your LMP now, that is only used before you get an accurate dating scan. Mine was also put back 3 days

Ok thank you! So baby is measuring from conception and not LMP? X

The dating scan is based on actual measurements of your baby, it's nothing to do with LMP or a potential conception date. They will literally look at the size of your baby to determine how far along in the pregnancy you are. Is there a reason you're so concerned about the supposed 3 day discrepancy?

I’m reading too much into stuff & this is my first time so I’m just confused as to how this all works if I’m honest…

I’d just ignore lmp or potential conception dates now. You are right tho that 4 weeks pregnancy is really only 2.

a dating scan is going off measurements of your baby to work out the gestational age and often isn’t exactly the same as LMP. NHS ei use your dating scan as your due date - which still has a 2 week window either side, it’s not an exact science.

Thank you for replying! I’m all over faced by understanding everything & lmp, conception etc. this is my first so not really sure how it all works. Just anxious and curious if I’m honest xx

Your dating scan is telling you how old baby is + 14 days. So basically your baby's age at your April scan was 11 weeks 6 days since conception.

Right ok, so if I’m 13 weeks pregnant I’m actually 11 weeks pregnant from conception for example. Sorry this is a lot to get my head round I’m not sure how it all works

Yes 13 weeks pregnant is roughly 11 weeks from conception, but you are 13 weeks pregnant & your due date will be roughly 27 weeks from now.

Thank you!!

I know it’s hard but try not to overthink and worry about the smaller stuff like this there’s so much involved with a baby that you can get bogged down in details, don’t worry and good luck with it all x

When they talk about 40 week pregnancy they mean 38 weeks from conception but 40 weeks from Lmp if indeed you ovulated on day 14. All talk of weeks will involve your baby's age +14 days once they have done an initial dating scan. Before that, they don't know exactly when you conceived so they just work of your lmp.

*Off

All scans are only a ballpark as babies grow at different rates anyway. +/- 3 days is very normal in terms of baby development.

My baby was ahead at times and then behind. She was IVF so I know exactly when she was conceived and implanted. Scans are only a guide.

What do you mean by +14 days? Like said before, if scan is showing 13 weeks it has 14 days already included in that? I like to understand things thoroughly and often get thrown off things. Sorry to be a pain x

Thank you! So even though it shows 13 weeks on scan it means things were conceived around 11 weeks ago? I ask as I like to understand timelines as best as, everything so far matches up within a couple of days and I just want to make sure everything is ok and as it should be x

That's exactly it. All dates will involve +14 days to theoretical .conception date. Pregnancy from conception is 38 weeks but 40 from a perfect 28 day cycle person's last lmp.