I had sex with my partner on the first day of my cycle is there a chance i can be pregnant?

Very small: Day one of the menstrual cycle is when the lining begins to shed. This occurs when the body knows that no pregnancy has occurred. Very occasionally a woman can release an egg around this time. It's very difficult to become pregnant during the actual menstrual cycle.

Pregnant on period: All physicians, and mother nature herself, have to say that there is some chance that pregnancy could occur, but it is very, very small--probably less than 1 in 10, 000. Nature can sometimes find odd ways to make pregnancy occur even under the most unlikely of circumstances. But i wouldn't worry much about it.