if my girlfriend is about to get on birth control, how long do we have to wait to have sex? also if i ejaculate in her while she is on birth control can she still get pregnant?

If a girl gets the shot, starts taking the pill, or starts using the patch or the ring within five days of the start of her period (the first day of bleeding), protection begins immediately. If she starts taking it at any other time during her menstrual cycle, protection begins one week later. Partners can use a backup method — like the latex or female condom — while they are waiting for protection to begin.

Used correctly and consistently, hormonal methods like the pill, the patch, the ring, and the shot are up to 99.7 percent effective against pregnancy. That’s why most men choose not to withdraw the penis before ejaculation while their partners are protected by hormonal methods. But remember, they offer no protection against sexually transmitted infections — only latex and female condoms reduce the risk of infection as well as pregnancy.

Hope this information helps!