Google it. Basically a purple line appears in your butt crack and extends upward the more dilated you are. I came across it on a YouTube video. I was checked last week and I was 0 cm dilated. This week (37) I did not get checked unfortunately. I have the line up most of my butt crack and it's super purple. I am not buying into it because I don't feel like I'm dilated. But have nothing to compare it to.  Maybe the line was always there - I don't spend a lot of time looking at my crack.   I took a picture of it since it's hard to see! 😂  anyone else feel like looking at theirs ? Let me know if it's true for you!