Dating question!

[Alicia870]

So according to my last period I am 14 weeks today.

Went for my first scan 3 weeks ago when I should have been 10 weeks but baby measured at 9. This was done by midwife who sent for scan with consultant which I had yesterday as she said they may need to change the due date.

So yesterday had the scan and crown to rump length measured baby at 12+6. Then he took the BPD measurement (length of head I think?) and baby measured 13+6. He said this is more accurate so I’m going with 14 weeks and keeping due date

Question is how common is this and why is the normal measurement they use showing up wrong then? Could my dates still be wrong? It’s probably not a big deal but would just be nice to know why this has happened and if it happens others too! Thanks

You can ovulate on days 10-16 so a week difference can be possible.

I don't really understand how they judge it as I was sure of the day I ovulated but they've dated me to 3 days before then, (so according to their due date I ovulated three days before I did ) which is fairly impossible.

My due date was changed at my first scan (brought forward by 5 days)
I've not been concerned by it or thought any more about it. I think it's just how much the baby has grown in the first 12 weeks really. No-one can absolutely pinpoint the date and time of fertilisation.

Hi guys totally get that but I’m just confused with why he’s not going with the crown rump measurement as that seems to be the main one they usually go with.

No-one on here can answer that for you, you'll have to ask your midwife about it.

My dates put me 4 days before I even had sex, it's only 4 days so not really that bothered. Only thing Im aware of is last baby was 7days late so if I go over again I get 10days before induction which is based on scan date but I know that's early so could be unnecessarily induced at 6days over.

Crown to rump length is less accurate because if baby isn't lying completely straight then the measurement can come up shorter where as their head circumference (BPD) won't really change whatever position they are in.