Help please!! Measuring 2 weeks behind at scan but sure of dates???

[3mum4]

Hi

So I know no one can fully reassure me but just wondered if anyone had similar experiences and could share outcomes!?

Background -

Have 3 children already - Youngest is 12 months old.

Menstrual cycles since DC3 had been all over the shop ranging from 29 days to 47 days in December cycle.

LMP was 2/1/23 - DTD on CD 11 and 12 thinking I wouldnt likely fall pregnant that cycle as I didnt get a positive OPK until CD 18. Had negative pregnancy tests on CD 30/31 and 34. Have not DTD since CD12 until after knowing I was pregnant (Partner worked away rest of Jan & Feb )

AF still didnt show up still by CD 58 so did another pregnancy test which came back glaringly dark positive.

Contacted midwife who booked 12 week scan for this week based on my LMP date but when I was scanned today I was only measuring 10 weeks.

I am stressing about it because whilst the baby had a heartbeat which I know is positive it definitely wasn’t formed to 12 weeks and just measuring “small” I could see the limbs were still just buds etc and the neck wasn’t properly there so I believe they measured correctly and its only a 10 week fetus but I can’t understand this as I know I only DTD twice on those dates in Jan so Im worried that the baby isn’t growing at the correct rate. Ive had the measurements be out by a few days in all my pregnancies but not by 2 weeks and because I know when I must have conceived it really doesn’t add up!

Can anyone with better knowledge/experience help unpick this for me so I can have realistic expectations when I return for a rescan in 2 weeks.

Thank you!!

Do you think possibly you ovulated CD20 48 hours after surge and then implanted late on day 12 to CD32 would that account for most of the 2 weeks and then the rest could be that natural margin of error. My date was moved 5 days later on dating scan. I know the go from LMP but realistically implantation happens 6 to 12 days post ovulation so that's nearly a week x

Yes I guess late ovulation and longer time for implantation etc is totally feasible for throwing the dates off but its then the length of time between last DTD and supposed ovulation which is throwing me off because I was sure I’ve always read there was a cut off of about 5 days for how long the mans swimmers were meant to last 😳

I think some websites can say they can last up to 7 days but I think its a really low percentage but it does only take 1 x

I ovulated 5 days after dtd and got pregnant, so I expect you probably ovulated late like you’ve calculated which would account for a week.

growth isn’t linear, wait until your 12w x

With my first I had a regular 28 day cycle. I tested the day af was due and got a positive. At my 12 week scan I was measuring 2 weeks behind. Which would work out that I conceived around the same time I got my BFP which obviously wasn’t possible. She never caught up growth wise and was born an average weight, perfectly healthy and is now 11 years old. I have no idea why she was 2 weeks behind but it was fine.

Update for anyone in my position in future because its nice when you are searching forums for reassurance to see the outcome!

Went back at 12+2 based on first scan dates for a rescan and all was ok! Baby measured 13+1 instead this time so had bumped forwards again a little decreasing the gap so original dates weren’t quite right but baby wasn’t as small as originally thought.

thanks for the replies x