What is the length of the birth canal?

The birth canal or vagina is 4 to 7 inches long. Vagina length varies from woman to woman, and the vagina expands in length and width during sex, according to Women's Health Magazine. During childbirth, it stretches to let the baby through, but regains its normal size later.

The birth canal is between the vulva and the cervix. It normally produces a clear or white discharge that keeps it moist, says Women's Health. This, however, changes during ovulation into clear, stretchy cervical mucus that signifies ovulation, the time a woman can get pregnant. Any other type of discharge is the sign of a possible infection.