Cervix - Anatomy & Function
The function of the cervix is to allow flow of menstrual blood from the uterus into the vagina, and direct the sperms into the uterus during intercourse.
The opening of the cervical canal is normally very narrow. However under the influence of the body hormones and the pressure from the fetal head, this opening widens to about 4 inches (10 cm.) during labor, to allow the birth of a baby.
If the opening is loose, as observed in some women, it can lead to miscarriages during pregnancy.