Not sure what you are meaning. I believe it's your guess?
My guess is the answer to melove's question is same percentage as non-pornstars and it highly depends on the region. Quick google search gave me detailled statistic tables.
Roughly like this: More developed regions worldwide 9%, EU 13%, NA 10%.
Please keep in mind I'm not in the biz. If there is some insider knowledge behind your question, then you can probably ignore my answer.
Anyway, my question was a little bit different. If an usual couple at home is not on birth control and wants some fun then I expect they will use a rubber in the majority of cases.
But in porn you don't see rubbers. And I read a surprising number of professional porn girls are not on birth control at all. Sounds brave to me in case it's true.
Someone with some insider knowledge here?