I am a guy so obviously periods aren't my expertise...

But I have been dating this girl for over 4 months now and she has yet to have had a single period while we were dating. I talked to her about it and she says its normal for her and she generally only has around 4 periods a year. I didn't want to pry too much into something as personal as her period but I had a couple questions about it so I figured I would ask them here.

First...Is this a common traight? I've never heard of it before. I've always thought most women, even if they didn't have a by the calender schedule still had semi monthly periods.

And second...Would something like this make it more or less difficult to become pregnant?