I always have exams on my birthday (June 7th) although on my 18th, it was technically in half term, because of the Golden Jubilee, and it was the day we beat Argentina!
This year I've got my steeplechase on it.
For GCSEs I had Maths and French, and got A* for both, and for AS levels I had M1, and got 100%, so I was pretty chuffed, but don't think it was just cos it was my birthday!