Can the linea nigra be a first sign of pregnancy?

Di

Took a test Saturday and it was negative. In my third cycle after stopping BC. First two were 22 and 23 days. Today is day 29 w no period. Breasts have been extra sensitive and heavy feeling. And today I noticed this line. Pardon my stretch marks and not thin tummy but I’m no stranger to stretch marks and I’ve never seen anything like this. I thought maybe ink from a pant seam had rubbed off. Or maybe a vein, but this is more black and so straight versus my one spider vein for comprising that is very squiggly and blue.

Ironically my Mom, who is newly battling stage 4 lung cancer, asked me today how TTC was going. I told her I doubted anything bc we only had intercourse once this cycle with everything going on. Told her my boobs did hurt though so thought maybe my period was coming. She randomly asked me if I had a line on my stomach and I showed her what I found this morning. She’s convinced I’m pregnant! I’m glad she’s excited but hearing this line comes much later for most women. I know it can occur without pregnancy but would it really come out of no where after 34 years? She said back in her day this was one of the first signs to look for. Has anyone experienced this as a first sign? I’m going to retest tomorrow but am debating if I should call my obgyn for a blood test if it keeps coming up negative.