Early scan - date confusion

[JoEW]

Hi, hoping someone can shed some light on this: I should be nine weeks and one day, due to the date of my last period (10th March) but I had an early scan today (as I had some bleeding) and they put me at six weeks and four days.

This seems impossible, I had a positive preg test five weeks ago. The hospital seemed pretty certain, despite me saying it didn't make sense and muttered something about late ovulation. I'm guessing this means the baby is small, should I be worried? I want to ensure the dates are right for the forthcoming tests. Any advice welcome. Jo.

If you can afford it, and they are not that expensive, why don't you book in for another scan privately in another two or three weeks. That way you will be able to tell if the baby is growing at a normal rate which will probably reassure you. So long as the baby is looking as it should do at 6 plus 4 its probably all fine. Good luck.

Hi JoEW here is a useful link for how early dating scans are done:

of gestational age

From what you've said there does seem to be a large descrepency in dates. It may be you ovulated late/twice.

Congratulations btw

Hi JoEW,
I have a similar situation, but the other way round (they said I am 3 weeks further on than I think I am).
I posted a question a few days ago and some other posters had similar experiences, here is the link in case there is anything useful there for you
www.mumsnet.com/Talk/pregnancy/963293-How-accurate-are-dating-scans

its very common to go for your scan and have your dates changed to being less pregnant than you thought you were. my dates that go with LMP are always a good 2/3 weeks ahead of the actual age of the actual baby. i aparently ovulate very late in my period, virtually a day or two before im due. i wouldnt worry about it, it doesnt mean the baby is small, like they said, late ovulation.
you can get a positive pregnancy test that early, when its happened to me ive got a positive pregnancy test within a day or two of being 'due', but then negative ones for a week or two until i get a positive result, and im currently 35 weeks pregnant with DC3

Thanks for the advice, it's my first pregnancy and there's so much information out there. Good to know there are others with similar experiences. Thought I would be very chilled about it all but it seems not! Jo.

my daughter had a similar experience,she worked out her last period was on her boyfriends birthday,so we knew the date,but when she went for an early scan due to a scare,they put her 2 weeks behind her dates ??? they told us she was due the 10th of december,she went for another scan and was told it would be christmas eve,and that she is now 11 weeks,its all confusing..

It really is all very confusing trying to get this dates accurate!

I have a 32-36 day cycle (averages at 34 days) and my LMP began on 11 April.

According to my iPhone app my fertile days on a 34 day cycle, were between 25 April to 1 May. My app suggested ovulation on 30 April.

I could have conceived on either the 25 April or 1 May as I recorded nookie in my iPhone app .

The GP says that I am more likely to have conceived on the 25 April as the sperm could be hanging around, rather than my conceiving the day after ovulation. But the Mumsnet Due Date calculator suggests the 1st May, and well, I tend to think this would be more likely too...

I am now going for my Nuchal Scan (which I believe needs to be done between 10-12 weeks). My scan date in 7 June.

According to my GP's estimated DD, I would be 8 weeks and 2 days on 7th June. Isn't this too early for a Nuchal Scan? The form I took to reception had my LMP incorrectly listed as a month earlier, so I called to tell them of the error and the 7th June date for the scan is my revised date (?!?)

This only gets more complicated when considering my my longer cycle length, and using the Mumsnet DD calculator. At the time of this scan, I would only be 7 weeks and 2 days.

Aiiiiiiiieeeeeeeeeee!! Apologies for all the details, I just really could do with your thoughts on this matter. I don't know if I should be calling and cancelling and asking for another date. Or if I should just go ahead with this one? Will I be invited back at the right time for the Nuchal Scan if I am too early??

All very overwhelming, and no-one to turn to (except Mumsnet of course!!)...

JoEW - Are you going back for another scan? I think you need to.

A pregnancy test will only show positive after implantation, which happens about a week after ovulation & fertilisation. So assuming that they are using the normal dating system, and not dating you from conception (which would be strange), if you got a positive test 5 weeks ago, you would need to be at least 8 weeks pregnant now for that to be possible (5 weeks + 1 week for implantation + the spurious 2 they add on to make gestation 40 weeks).

So unless you were wrong about the test, it doesn't sound great I'm afraid.

Podpod - do you know that you have a shorter than average luteal phase? Or where you temping? If not, I can't see how your app worked out your fertile dates. Using an average LP of 14 days and a typical cycle length of 34 days, you should ovulate on CD20. If your LMP was the 11th April, then you should have ovulated on or around the 21st April.

And the nuchal scan should be done between 10 and 13+6 weeks afaik. 7 or 8 weeks is too early to get accurate readings - I had an early scan at what I thought (from LMP) was 8+3 but they thought I was probably a bit less than that (fits with my typical pvulation pattern) and said it was too early to get accurate measurements even just for dating.

Hi Japhrimel - no, I was unaware of that...

I guess my phone app isn't flawless then

I am mightily confused. Based on your calculations - it's more likely that I conceived on the 25th April and not 1st May...

If you don't mind me asking, were you offered another scan following the one you went to that was too early? I am just wondering if I should be phoning and cancelling, but not feeling very confident in my actions or calculations right now...

If you go for your nuchal and measure too small for them to do the scan i.e. less than 10 or so weeks they will rearrange for the right dates. rememeber that dating by scan is not so accurate incredibally early in gestation which is why it is usually done at around 12 weeks, so your dates my well get changed at your next scan.

Either way, congratulations!

My scan at 8 weeks was private and done just for reassurrance (although they did their best to help date me better). I'm still getting the NHS dating & nuchal scan at 12 weeks.

I would rearrange the scan TBH.