Birth control works by preventing pregnancy. If you are already pregnant, birth control is of no use.

The birth control pill decreases the risk of pregnancy. That is what it is intended to do.

You can take a pregnancy test any time you like. Birth control does not affect the accuracy of a pregnancy test.

Prenatal vitamins are to make sure you have enough vitamins and minerals to support a pregnancy. Birth control is to prevent pregnancy. They have different purposes. Birth control does not support a pregnancy, and prenatal vitamins do not prevent pregnancy.

With a pregnancy test.