greenkat

I had one last week - when I was 22 weeks. They do it as standard between 22 and 24 weeks at my hospital (as long as you want it of course).

They measure the cervix to see if it's short. If it is it can mean you go into labour prematurely as a result - before 33 weeks - so they'd say you're high risk and do more checks on you. Mine was apparently normal at 27mm.

It was minimally invasive - she said go behind the curtain and take my bottoms off then cover myself with the sheet provided. Then when I said I was ready she inserted the scanner thing, with a condom on, about an inch and didn't even touch me herself. - It was really quick too so not too bad.

xXDonnaXx

I've not had one either.
I go to see my midwife in 5 weeks, but that's just for antenatal.
I'd ask to see why they want to do it.

CamoQueen

I haven't had one in the second tri (my first ultrasound at 10 weeks was internal), though I hear it's the best way to measure the cervical length. I know at my ultrasound a week and a half ago they measured the cervical length along with everything else...

Honestly, I would say the more vigilant they are on checking for potential problems, the better!