Confused about ultrasound dating

[bouncingblob]

We had an early ultrasound recently at 7 weeks 5 days (based on LMP).

However all that could be seen was a gestational sack and yolk sac, and it was dated around 5 weeks 4 days.

This is where the confusion starts. We know that 5 weeks 4 days is pretty much spot on for the actual age of the foetus as I was tracking ovulation, which would be around that time ago. But we also know that how long you're pregnant is dated by your LMP - in which case we're closer to 8 weeks.

Should we be worried about this? We're due to go back in 2 weeks for another scan. But we can't figure out whether the development is behind where it should be. If it's based on LMP, it is. If it's based on conception, it isn't. Help please!

Mine kept being dated behind a bit, so i had a few early scans privately..all had different due dates. On the 12 week scan it seemed to have a growth spurt and was then where i thought. Think in the early weeks it is all a bit of guess work.

LMP is used because it’s the fixed point that most women can clearly identify. But if you ovulate late in your cycle or have a longer cycle (as it sounds like you do), then it’s definitely more accurate to go by ovulation date if you know it. Many women don’t track ovulation (and the ability to do so accurately is quite recent) so they’d have to use LMP. I think everything sounds just right for you and you’ve got nothing to worry about.

Thanks, I know I did ovulate later in this cycle than in previous months of tracking (although only about 3-4 days late). It took a long time to get a strong positive pregnancy test as well, it was still just a faint line even a few days passed my missed period. Though I tested a few days before the ultrasound and it's a very strong red line now! It's all just very confusing in relation to the timing and then you worry about miscarriage and empty sacs and all that sort of thing

Going through the same right now. Went to an ultrasound at what should be 8 weeks but I measured 1-2 weeks behind and no heartbeat. I have another scan on Wednesday to check for growth.

Wishing you the best of luck! X

Did you see a fetal pole or heartbeat? I think we're panicking because there was nothing other than the G sac and yolk sac. The tech thought there MIGHT be the beginnings of a fetal pole but it was so small they couldn't be sure.

Hi everyone. I had this, measured 2 weeks behind at a private scan, went to NHS and was still 2 weeks behind (6 as opposed to 8) but there was a HB. unfortunately at a scan two weeks later there was no growth, and no heartbeat.

I also reached out for stories and heard both good and bad outcomes - I really hope yours are good outcomes x

@bouncingblob We only saw a very small fetal pole and there was blood flow to the baby but no heartbeat seen. Tech said it might be too small to see it.

It can be confusing, can’t it, and everything’s so tense at this early stage. Remember that the medical measurements add 2 weeks to the actual conception date (this is what measuring by LMP does in theory, but of course ovulation isn’t always day 14!). Can you share the actual dates of your ovulation?

Yes, I was testing positive around 21st-23rd December. That was a little later than normal according to the tracker. I know as well that the ovulation strips don't necessarily predict the day of ovulation but it can be 24-48 hours after that so I may have actually ovulated as late as 25th-26th December.

The date of when you ovulated will correspond to the actual age of the baby. Dating by LMP is what tends to be done until the 12w scan - and then that date is taken as your real due date - but can be very inaccurate for women with long / irregular cycles. One of my friends got pregnant while she was breastfeeding and her cycles hadn’t come back properly, she would have been 4 months by LMP but was actually only 7 weeks! I have PCOS and irregular cycles and ovulate late - I have always dated my pregnancies in my mind by my date of ovulation and this has tracked my scans much better than LMP. X

The day after ovulation day (1dpo) is classed as exactly two weeks pregnant. So as you know your ovulation day, work forwards from that, how far were you at your scan yesterday?

LMP dating only works for those who have a classic 28 day cycle and ovulate on day 14. If you ovulate later in your cycle (and SO many women do), then you go to your first scan and get all worried because you’re ’dated behind,’ but you’re not behind!

Work it out like I explained above and let us know what it is 😊

And when did you have the scan dating 5+4?

Based on that (2 weeks being 1 DPO) I would have been 7 weeks on the date of the scan but I dated 5 weeks 4 days.

Ok, that makes sense. 1 week 3 days is closer then than the 2 weeks you thought you were out initially, which is a bit better.

At such an early stage it’s just mm they’re measuring, and that can make all the difference. From a quick look online it seems you might expect to see a fetal pole between 5.5-6.5 weeks.

You’ve probably seen various stories on here of people measuring behind without explanation, either for a bit at the start or throughout their pregnancy, and things being fine. Or it could be you actually ovulated a bit later than you thought, even though you were testing. I guess late implantation might be a factor too? But then it could be a sign of an embryo developing very slowly, and the pregnancy unlikely to be successful.

I’m afraid there’s probably nothing for it but to wait for the next scan, and figure out how to look after yourself as much as possible between now and then. Good luck x