Purple line.

It means absolutely nothing I promise

I had the line too when I was far along in my last pregnancy and never ended up dilating lol (baby turned breech so had to have a c section). I think it’s a myth!

You mean the dark like on your butt crack/lower back in a vertical line? When I was giving birth to my first I had a water birth, was 18 and obviously didn't know what I was doing but my body told me to push and before I did I asked my midwife if it was OK, she said she can see I am dilating, by that line on my butt.. I never really thought about it till I just read this, but I also never checked whether or not I had that line before I went into labour. If you're worried, please go and get checked. Best of luck