My wife wanted me to mention that we had a baby boy five months ago and that he was born with no markings at all. This was something that we, mostly my wife, worried a lot about both before and during the pregnancy.
I know it's something that a lot of us worry about after dealing with a child with an H, so just thought we'd throw our two cents in. I know there are no hard and fast rules or statistics out there regarding this.
All the best.