Birthmark?

Iv

I’ve notice this stain on my baby skin when she was born I just thought it was peach fuz but now that she’s growing I notice that it shows more . I mean I don’t mind if it’s a birthmark that color or size I’m just worried that it may grow bigger and darker . I don’t have a dr appt for her until next month to ask her pediatrician. Does any other mommy’s notice anything similar with their babies ??