I was told they would only do them between 4 and 6 cms, then they said 'ooh but if you let us hook up this syntocin you can have one now'
It seems they may be a moveable feast. But they take up to 20 mins to take effect in any case, and that's if you can get the person to come put it in immediately.
I'm having an epidural for the conception next time and leaving it in till the little bugger starts school.