Can a docter tell wether you were on or off your pill?

If I told my doctor I had been following my birth control some what faithfully (with the expection of doubling up acouple of times) could he know if that were true? Wether I was on the pill or not, if I missed a pill (OR NOT) and/or when I took my last pill? Basically could my doctor tell that the cause of the pregnancy was the fact that I stopped taking my pills (even if i dont tell him I stopped)?