A common worry of pregnant women is whether there will be pain when the baby exits the vagina.

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The Vagina and Human Reproduction

The vagina plays an important role in human reproduction, though it's certainly not the only star of the show. While the vagina is involved in the beginning of the process -- by giving the penis a place to release sperm -- and it's certainly involved in how a baby is delivered naturally from a woman's body, the rest of the tasks fall to other organs surrounding the vagina: the ovaries, fallopian tubes, uterus and cervix.

A woman's eggs are stored in her ovaries, and each month, the ovaries release an egg that makes its way through the fallopian tubes. The uterus begins preparing itself to house a growing fetus by accumulating a lining on the walls. If the egg remains unfertilized, it is expelled, along with that uterine lining, through the cervix and then out through vagina as a menstrual period.

But let's say a woman has sexual intercourse during the time in which she is fertile, and semen makes its way from the vagina into the cervix. The sperm swim through the cervix and into the fallopian tubes; once the egg is fertilized, it makes its way into the uterus for approximately nine months of development.

Childbirth begins when the uterus starts contracting, which signals to the cervix that it must begin dilating. In other words, women aren't waiting for their vagina to stretch during hours of childbirth -- the vaginal muscles are ready at any time to expand. Once the cervix is dilated -- or, expanded far enough -- is when the baby can move through the cervix and into the vagina. Because the vagina is that last step on the baby's journey, it's often referred to as the birth canal.

It is possible, though not common, for a woman to experience vaginal tearing during childbirth. Tears are more likely to occur when a woman is having her first vaginal birth, or if she's having a vaginal birth after previously tearing. Episiotomies and bigger-than-average babies are also risk factors. There are various degrees of tearing -- nicks at the top of the vaginal canal may require stitches and cause pain for several days, while tears in vaginal muscles and perineal muscles are much more serious.

For centuries, the vagina was viewed primarily as a reproductive organ. On the next page, we'll consider the role it plays in sexual pleasure as well.