I think the focus on dilation is really more medicalised timeline stuff than anything else. If a woman is labouring you can see over time how her colour, mood, needs, introspection or otherwise, and so many other things change over time. With a known careprovider, your MW should know you well enough to see these changes occurring - or not - in you. The whole package is much more important than measuring dilation by VEs or other means. And a measurement of dilation tells us nothing other than how far you've dilated. It doesn't tell us about your emotional state, or how much longer you might be labouring. Some women take days to dilate fully others will make huge leaps in minutes. So measuring dilation doesn't help in either scenario really IMO. For me, measuring dilation or a VE to check on a baby's head position is an intervention best saved for maternal request, if she has a feeling something isn't right or it's agreed that it needs investigating. Otherwise I think the best way to judge dilation is that there's a baby coming out

The purple line which extends up between bum cheeks only happens in some women and there isn't any research into it that I've seen

There are some articles I think. This is one:
Hobbs L (1998). `Assessing cervical dilatation without VEs Watching the purple line', The Practising Midwife, 1, 11, 34-35.
These are about VEs and other ways to judge labour progression instead of them. Hope they're helpful
http://www.radmid.demon.co.uk/suehanson.htmhttp://www.radmid.demon.co.uk/guidelines.htm
In Midwifery Matters, Issue No. 81, Summer 1999
INVADERS OF PRIVACY Chris Warren
Checking your own dilation if you want to:
http://www.joyousbirth.info/articles...xlearning.html