Port Wine Stain Birthmarks

My now 7 year old was born with two Port Wine Stain birthmarks. A tiny one on her forehead and another that spans her entire left hand. Over the years they have faded considerably. The one on her face is completely gone. The one on her hand only slightly visible. My question is this:
Am I more likely to have another child with a port wine stain birthmarks or is it all up to chance?