Can anyone explain to me how a dating scan can use size to date an early pregnancy and also give the size as a percentile?

[BellaBearisWideAwake]

Hi, I just had a dating scan where it was confirmed that I am 8+2, as far as I could make out because of the crown-rump length. And then on the report it has what I assume is a line representing the length on a percentile line, with a marker just below the median/50th percentile.

So I was wondering how they can do both? Does that make sense? It's just idle speculation really, not important at all.

Thanks in advance!

[SaorAlba]

Sorry, I can't help, but you raise a good point.

You are right, it is completely illogical.

I'll also be watching for answers with interest! I'm 8+6 today so just ahead of you, but I'm not getting a scan until 12 weeks :)

[BellaBearisWideAwake]

We'll wait and watch together!

I had a private scan as I recently had a mmc and I'm nervous as hell this time round.

[addictedisgettingexcited]

bella i want to know the answer too!

i was scanned and put on the middle line and told how far along i was (i'm now 30+3)

but according to my dates i should be 31+3 which would put me on a lower centile, but still a healthy pregnancy

i thionk they just like to put every one in the middle and hope for the best

[onimolap]

In the first 12-14 weeks, babies are forming up from the initial ball of dividing cells, developing spine, arms, legs etc. This growth is constant and therefore measuring it tells you how long the baby has been growing for, this confirming gestational age. The 50th centime is the standard human growth pattern.

Small deviations from it are disregarded (probably down to exact ovulation date and conception moment), and dating will continue from LMP. A big variation usually means your dates are wrong.

After about 14 weeks, growth is about getting bigger and stronger, not forming the body) and individual genetic growth pattern takes over and the range of normal growth becomes much more variable.

[BellaBearisWideAwake]

Thank you onimalop. I get the whole size = age thing before 12 weeks. Does that mean that the size combined with my LMP are consistent with 8+2, but that of all the 8+2 sizes recorded, this baby is at the 48th percentile?

[SaorAlba]

Bella Maybe you're 8+2 but conceived 30 minutes later than the average 8+2 (or had your scan 30 minutes earlier) so your baby is just ever so slightly smaller than the average?

Sorry to hear about your mmc, thinking lots of sticky thoughts for you this time around :)

[onimolap]

Bella: yes.

It's all based on a 28 day cycle and day 14 conception, that's why small variations are disregarded as they would mean no more than normal ranges for cycles. And given that normal pregnancy can vary from 38-42 weeks, it really doesn't make a difference.

[BellaBearisWideAwake]

thanks!

(yes,I know it doesn't matter at all! Just curious)

[nomoremagnolia]

[BellaBearisWideAwake]

thanks my lovely! 4 more weeks and then hopefully can come clean to the masses!

[robino]

Good question! I was pondering similar questions after I had two scans in the same day (same member of staff, same equipment; apparently there was a missing measurement so they asked if I wouldn't mind going back in a couple of hours later). Scan one put me at 12+0; second scan put me at 12+3. Doesn't particularly bother me but it put my midwife in a right tizz yesterday!

[MumNWLondon]

I think if the scan roughly agrees with your dates, they keep your dates and then you get a percentile which isn't 50th... or the scan doesn't agree at all in which case they give you a new EDD and its on the 50th percentile.

[BellaBearisWideAwake]

ooh, more answers! MuminNW, I think your suggestion makes sense

[BellaBearisWideAwake]

why can I not remember a poster's name between reading their comment and writing it in my reply??

[nomoremagnolia]

Everything crossed for the next 4 weeks for you xxx Looking forward to the official announcement :)

[nomoremagnolia]

How's things been these last two weeks? Hoping you're still well, I still have everything crossed for good news at the end of the month. xx

[BellaBearisWideAwake]

fancy a facebook chat?

[nomoremagnolia]

Looks like I missed you on fb sorry