Second, even if a pregnant woman were to ovulate, sperm would have to get to that egg. But thanks to the mucus plug, sperm are blocked from reaching eggs in early pregnancy. (While this isnt the main purpose of the mucus plug, its bacteria- and infection-blocking properties work on sperm, too.)

What happens to sperm during pregnancy?

This means that semen from the male must be able to attain the ovule in the females oviduct. When a woman is pregnant however, a mucus plug is formed in the cervix, blocking the passage of sperm. This mechanism prevents semen from passing through the pregnant uterus, let alone allowing it to reach the oviduct.