White birth mark?

Lindsey • 24 years old married to my best friend. I lost one baby and I'm pregnant now! :)
Does anyone else's babies have a white birth mark. I noticed it on my daughters belly when she was 3 weeks old. It's a little whiter than her skin. She's two months now and it hasn't gone away. She has her next doctors appointment in a few days and Im going to ask her doctor.