Can dating scans be wrong?

[TotorosOcarina]

I had my dating scan a while ago and am still really confused.

I'm plannng my 3rd homebirth (4th birth) and my dates just do not add up and I'm worried about being seen as 'overdue' by the scan dates and not being allowed to deliver at home.

I wa going to be 13 weeks that day by LMP.

But by my calculations - the fact I OV day 21 and the date I got my BFP (after testing daily) I put myself at about 12+1

however scan said 10+4

even the midwife said it didn't make sense as by that dates I got my BFP at the time of conception!!

Sonographer said 'you are def 10+4'

No doubt about it- the scan is accurate to within a day or two (curled up baby can make you 2 days less than dates)Also a 10+4 baby has a distinctive look compared to a 13 weeker and as a Sonographer myself I have formed a 'guesstimate' in my head even before I measure the CRL.
Perhaps you ov'd later that month (can happen even if you're usually regular as clockwork)and preg tests are very, very sensitive nowadays...even before period is due.
Are you having another scan at 12w for NT- that might put your mind at ease if they both tally? Xx

That does seem very odd, but I though dating scans couldn't be wrong by more than a few days. Will be interesting to see how many weeks/days your 20 week scan puts you at.

Scans can absolutely be wrong. If by their dates conception would have occurred when you got your BFP then clearly something is off, no pregnnacy test in the world is that sensitive! A woman does tend to know her body best and although scans can be hugely beneficial in identifying many things I find it quite sad that we overrule a woman who knows when she fell pregnant with a piece of 'one size fits all' machinery.

No they didn't offer me another scan.

He was smaller than my babies have been at 12 weeks.

Even if I OVd later than day 21 I can't see how I got a BFP so early?

Can anyone figure anything out by my dates?

LMP 16th July

BFP 24th August.

scan date 14th october - 10+4

My 12 week scan put me back over a week (which, like you, didn't add up at all).
When I had my 21 week scan though, they put me back to my original dates.

I didn't particularly ask any questions about it, but it seems to me that my dates must have been more accurate than on he first scan.

What cycle day did you get your BFP?

Even if you typically ovulate on day 21, doesn't mean you did that cycle. Also, it is possible to get an LH surge but for it to not be strong enough to trigger ovulation, so you get another one later on. What were you tracking to suggest you ovulated on day 21?

My dating scan was wrong and I knew that my dates had to be right as I only had fertility treatment on one day. :)

LMP isn't a great way to calculate either though, as sometimes you can ovulate at strange times of the month.

If your midwife agrees that the scan dates can't be right, can she back you up that you aren't really overdue if the time comes?

I've been told that scans can be 5 -7 days out.

Oh - and my baby is an IVF baby and a scan I had at 16 weeks suggested I conceived a week before the IVF so YES they can be wrong.

Toto, by your dates, you could have easily got your bfp at roughly three weeks (thats when I got mine), which WOULD date you anything from 10+2 upwards.
Ignore your LMP date - you clearly ovulated later then the "normal" therefore the LMP date is completely irrelevant.

You are now 11.5 weeks, no question!

Lots of love and luck (and congrats!)

Toto,

I have heard that some women do they following when they are absolutely sure of their dates

-tell them you only had sex once, insist and get the date changed.
-scribble out the date on your notes and write in your own

just a thought...

Duellingfanjo

Wouldnt that scan result be about what you would expect? With it being embryo transfer rather than conception you would measure further on than as if you had conceived the baby that day?

No - I mean that from the scan size and the date it suggested it looked like my egg was fertilized a week before it was, if that makes sense.

I understand now

Duelling Fanjo, at 16 weeks yes, scans can differ from dates as growth rate begins to vary. I am talking about scans at 10.5-12.5 weeks- the most accurate time to date by scan.
DrMcDreamy, I have (and I'm sure you have) come across many, many women (not suggesting the OP here before I get comments back!!!!!)who disagree with their scan dates, even when they know they are right for 'social' reasons or because they want an earlier EDD. I think it is highly contentious to suggest that such an extensively researched, tried and tested method of dating is inferior to instinct alone!
Measurements aside, 10+4 baby does not Look like a 12+1 baby. Xx

Mine was wrong. If I had conceived when the dating scan suggested it would have to have been an immaculate conception as was on holiday with my bestfriend and not DH! Was 2 weeks out, corrected at 16 weeks but they still weren't convinced as that scan isn't deemed as accurate. As it was she arrived 2 months early!

my scan at 12 weeks also measured me 5 days ahead of where I really was. :)

Before scans were invented the only way to calculate due date was by LMP and it was assumed that you ovulated on day 14 of your cycle. That meant that the date you were given was calculated not from the date of conception but from two weeks before. Actual gestation is really about 38 weeks (that's why you're considered term from 37 weeks onwards). Even though we now have scans your due date still includes that two extra weeks, so if you know when you had sex add two weeks onto that and you have your medical "conception" date.

andyflo I have indeed met woman such as the ones you speak of. And ones who deliberately wet themselves in a bid to convince me their waters have gone to try and get induced at 35 weeks but that's a different story! I know that dating scans are reasonably accurate but I just meant that I find it sad that in situations such as the one described in the OP where a woman is sure of conception that we dismiss that womanly knowledge of their own bodies and insist on relying on machinery.

My scan at 12/13 weeks dated me 10 days before I actually had sex. Have been a bit worried that it means there's something wrong tbh.

Pushmepullyou if you read my previous post you'll see that that's exactly what you should expect.

Thanks writer, but I wasn't clear in my post I don't think

By the only date I had sex in that cycle i should have been 12+3 when I was dated ie 10+3 weeks from conception, but was dated as 13+5

Another IVF one here!

Even allowing for the embryo to be 3 days old when transfered, my scans are always nearly a week ahead! I said it was a medical impossibility as it was still in the deep freeze at that point! Obviously we know exactly when it was transfered.

My consultant agreed with me and changed the date after my 20 week scan as the midwife wouldn't, which was important as they are keen in this area to induce if you are late after just 10 days!