Trying to work out scan dates: help!

[JimandPam]

Hi guys.

I'm sorry if I'm asking such an obviously stupid question!!

I recently found out I'm pregnant and due to pre existing health conditions (under control and medical team aware) I'm told I need an 8 week scan. Nearest hospital do this as a walk in so no appointment needed and I won't see the antenatal team until after the scan.

So I'm trying to work out when this will be. The first day of my last period was 22nd October, I THINK I ovulated around 1st November. So I believe I'm now 5+5 pregnant (?) and the 8 week scan should be 17th december(?)

The reason I'm confused as I've seen a few threads where people have gone for scans for 8 weeks saying it has been confirmed that although 8 weeks since period, the scan puts them at 6+2 (or something) as they ovulated on xx date.

So should I go for a scan 8 weeks post estimated ovulation? Will the baby be 8 weeks when I go or 6ish weeks?

Sorry, this is so new to me and I've got myself in such a muddle!! Help ladies!

Not sure if this is helpful but I’ve had a 7 week scan and a 9 week scan (due to previous MC). My 7 week scan was calculated from date of last period, I went went I was about 7 weeks 3 days and I was told I was measuring 6 weeks 5 days.
I then went for my next scan at 9 weeks on the day (still calculating from last period), and was told I was measuring 8 weeks 5 days.
I am now 9+3 and I’ve been given a next scan date of 20th Dec which is the 12 weeker.
Just to note the first scan was private, the second scan was NHS at the EPU. I haven’t seen Midwife yet for booking in. X

@HayleyHaystack thanks so much for reply and sorry to hear this hasn't been an easy journey for you. Sounds really positive so far for you this time though and I do hope this continues!!

It does help thanks but I guess I'm confused in the difference between 'measuring' date and pregnancy date? So at 7 weeks you were measuring 6 weeks. Did this then mean you were 6 weeks pregnancy and your due date changed? And is it usual to be measuring less than how many weeks pregnant you are (this seems to be the norm on other thread but I find the whole thing confusing!!)

Thank you so much for taking the time to reply!!

If your periods are regular, your cycles are usually the same length and they are 28 days long, go by your LMP date. So, go for the scan when LMP tells you it's 8 weeks.

There are lots of reasons the baby might measure smaller on the day - difficult to measure something so tiny, ovulated late, implantation took a bit longer - but there's no way of knowing that. I'd wait for the professionals to give you a steer once they've done the scan. If it's a bit smaller than expected, at least it's a baseline and the most important thing is that there is progression between one scan is the next, not the dates.

In my case, my cycles are anything between 33 and 43 days. This means I ovulate later than 14 days into my cycle, so LMP isn't very helpful for dating.

PS the final pregnancy date is given at the 12 week scan, based on the measurements. Until then it's all guess work.

If you go for a scan 8 weeks post ovulation, you will be 10 weeks pregnant. Go by lmp date, you may be a few days out but that's neither here nor there really. My lmp was 21st October but I know I ovulated 7/8 November. So although I am 5w6d by lmp, I know I'm really more like 5w2d. But for the sake of 4 days I'm not going to worry. I have a scan booked for next Sunday where I will be 7 weeks by lmp. But am expecting the baby to measure nearer 6w3d ish. Hope that makes sense?

My measurements were way off for two early scans. All was resolved at the 12 week. The early ones are just so small, the tiniest discrepancy throws the dates right off. You should go for your 8 week scan 8 weeks after your period.

If you’re certain when you ovulated, go 6 weeks after then as they’ll basically add 2 weeks on from there. If not, go on 17/12 and they’ll date you and tell you when to go back for nuchal test etc

Congratulations

Guys, I can't tell you how reassuring you have all been! My periods are very regular but usually 24 days so I think I'll stick with LMP as date.

I'm just so anxious about this first scan due to my other health issues that I'd hate to be turned away and told it was too early to tell if positioning was ok, heartbeat good etc.

I understand a little more now so thanks so much for unjumbling it all for me 😊

Good luck!

In case helpful, I'm currently 8+3. First time they saw 'something' and confirmed it's in the right place was roughly 4.5 weeks. At 6+5 there was a heartbeat. They'll make another appointment for you if they don't see enough. It's quite interesting seeing all the scan stuff, like another planet!

Hello @jimandpam well I thought they would have moved the due date but because it’s so early they kept it to 4th July. Basically they said it’s too hard to get the measurements bang on. I found it all very confusing. I guess at 12 weeks is when they will properly date it?

Scan dates should be calculated from lmp.

I’ve never inderstood why some hospitals change due dates from scans. The tiny mm they’re measuring means a week either side could be standard error. Stick with LMP unless it’s at least 2 weeks out, in which case date of lmp is likely wrong.