No sign of any teenage pregnancies at Hogwarts yet. All I can report from the fourth book is that they have faced the grueling task of choosing a member of the opposite sex to take to the Hogwarts Christmas ball. I think Harry feels, alongside many fourteen year olds, that he'd rather face a flame throwing dragon than ask a girl to the ball. All in all he might get his first kiss by the age of 21, we wait with baited breath.