What is the earliest you can be dated from a scan?

[Star82]

Good morning girls!

I have an early dating scan booked today as I have no real idea of my dates. LMP was July 12th and I tested positive on October 7th.
Does anyone know how to work out how pregnant I could be if October 7th was, for arguments sake, the earliest I could have tested positive?
I'm a little worried that the sac could potentially be too small to date. Can this be the case? Obviously could also be further along but concerned it could end up being a waste of money if I am at the lower end of the scale.
Can anyone shed any light on this? Thanks.

Morning. My maths was never any good so can't help with dates... But scanning they can do from as early as 6 weeks and get a heartbeat. I had one done at 6 weeks in my last pg, so know that's possible. We saw the heartbeat but unfortuantly ended in MC a week or so later. I'm 38 weeks pg now and wanted a reassurance scan done this time... They advised me to wait til 7 weeks as although can be done earlier, by 7 weeks you're more likely to see the heartbeat and the foetal pole. I can imagine if you go too early and don't see what you'd hoped for, it is likely tocause sone distress, even if everythings ok and you just got scanned too early. Good luck! HTH.

Actually, even with bad maths, if your LMP was July 12th, you should have been due on roughly one month later, if you're regular.... So august 12th approx. So looks like you could be as much as nearly 11 weeks!!! I think a scan will be absolutely fine by now x

If October 7th was taken as the day you forst tested positive, so approximately 4 weeks pregnant, that would make you due around 16th July.
I've had early scans with my pregnancies but they have never put a proper due date estimate on until the 12 week scan, they said they cannot be close enough earlier on, although they say roughly 6 weeks/7 weeks etc depending on the size.
Hope all goes well.

Thanks excitedmummy. I don't think i'm as far along as that as i did a test in august which was negative and also one very early september. I would be hazarding a guess that conception possibly would have took place mid september but it's just so hard to know.
Thanks littlemiss also for taking the time to reply.

How dark was the line when you tested?

If it was faint (almost have to squint to see it) on 7th October, you might only be 10 days past ovulation, which would make you 19 days past ovulation today - 4w5d.

You can sometimes see a gestational sac at 4w5d (it would be about 5mm or something crazy!) but it would be too small to date accurately. Ideally you'd need to be about 6 weeks to get better accuracy. Having said that, from about 5w3d or so when the sac is a bit bigger and you can maybe see a yolk sac so dating is a little more reliable.

Of course if the line was quite dark then so long as the pregnancy is fine, the dating should be accurate.

Good luck!!

Thanks sparklies. It was strong on the 7th and then said 2-3 weeks (so 4-5 weeks) on sunday 3 days later. It said the same this morning.
They couldn't really see anything apart from what they thought could be an early sac. I'm to go back in a few weeks free of charge for another look. I've still got another digital test so will test next week to check hormones still up and it's then just a case of being patient and waiting for the next scan.

If the CB digital is accurate (which it isn't hugely.. apparently the least accurate reading is the 2-3 weeks one!) then on the 7th you'd be at 14-21 days past ovulation. Which would put you at 22-29 days past ovulation for the scan. That translates to 5w1d to 6w1d.

Was it an internal or an external scan? External you wouldn't expect to see a lot!

Internal you can sometimes see just a sac even at 6 weeks and everything is fine.. early ultrasounds are +/- 5 days of accuracy. So everything could well be looking good - just harder to date. The most accurate date comes from measuring the baby which is usually only visible from 6-7 weeks, 6 at the earliest.

For what it's worth, my HCG levels were really high (above average for triplets.. there's only one in there!) and that CB digital said 2-3 weeks when I was 5w1d.. really it should have said 3 weeks+ at that point especially with my high levels! So don't worry too much there.

Glad you can go back for free - hurray! Fingers crossed for you. I know only too well how tough it is at the start.

Thanks so much Sparklies. That has really helped.

I've really been giving myself a headache trying to work out how many days following conception you would need to be to test positive, so you've helped so much with that. If i had to be say 5.5-6 weeks yesterday, i'd be a little concerned at the scan not showing anything.

It was an external although they offered internal but she said they may not be able to tell me much more with that. I decided to opt for another external one than have the internal one.

This morning it has changed to 3+ weeks on the last test i had. Last sunday it changed from being 1-2 to 2-3 on sunday so for arguments sake, say the tests are accurate, it would make me 5 weeks today.

Its seems mad that it wouldn't pick up on hormones from all 3 babies. These things are good that are being developed but it goes to show they can be more hassle than its worth.
We were only really interested in a due date as we can only holiday in June due to DH's work. No time off apart from then. Was hoping i'd be due early on so we could maybe get a little UK break in for the kids but it's looking unlikely now. Will maybe have to take them away on my own somewhere before or after with Dsis or other friend/family.

Thanks anyway. Much appreciated!!!

Sounds like your HCG is going up fine so everything sounds good!

Yes, with an external you'd be lucky to even see a sac! Externals before 8 weeks are usually a waste of time.. internal is the way to go, although yes, before 5w6d you don't usually get an accurate date either.

Those tests aren't actually licensed in the US.. not 100% sure of the reasons why but I think it's because they're just not accurate enough and they could scare women when nothing is wrong.

Yes, June doesn't look like an ideal time to have a holiday for you right now! Oh dear. We're planning on moving house in July so I was relieved we scraped in due in May.. if we'd been unlucky that cycle we'd have had to postpone TTC for months I think!

Hope everything goes well :-)