linea nigra any idea?

I just googled what does it mean to have dark line on belly like- from pelvic area to near belly button vertically, it’s called linea nigra,, but google says it appears only after 5 months during pregnancy. Why m getting it? I am just in week 4 🙆‍♀️ any comments or experience?

Sorry forgot to mention in original post that I am doing IVF and currently in two week wait so asking this question. Not intended to hurt anyone. Just curious to know if linea nigra is sign of pregnancy? My beta is still days away. Getting anxious.