Basic Vocabulary:
Contraction- A contraction is the flexing of any muscle in the body. During labor, it specifically refers to the flexing and pulling of the musles in the uterus to dilate the cervix and push the baby out.
Uterus- Also called the womb, the uterus is a large bag of very powerful muscles, which holds the baby during pregnancy and pushes it out during birth.
Cervix- The word cervix literally means "neck." It is the neck that opens to the uterus and closes it off from the vagina. It remains closed during pregnancy, but during labor, the cervix dilates (or opens) wide enough to push a baby out.
How Labor Starts:
To prepare for labor, the cervix must ripen, efface, and begin to dilate. These generally occur in the final weeks or days of pregnancy, but may occur earlier or later in some women. When it ripens, the cervix becomes softer, preparing it for effacement, or flattening. As the cervix effaces, small amounts of tissue are shed, thinned, and flattened and the cervix changes its form. Effacement is measured by percentage. At 25% effacement, the cervix has lost a quarter of its thickness, and at 100%, it becomes a very thin membrane.
The signs of impending labor are different for every woman. The bag of waters, or amniotic sac, may break before labor begins, but this only occurs during about one in ten births (in spite of what sitcomsmight have you think). Some women experience "bloody show" or a discharge of blood and mucus before labor begins if their cervix is dilating or effacing rapidly, but others do not. In most cases, a baby becomes engaged, or drops lower into the pelvis, before the onset of labor, but this also does not always occur. The beginning of labor is completely unique for every situation.
Braxton-Hicks, or practice contractions, become more noticable and uncomfortable when labor is about to begin. These uterine exercises are not real labor, but they help to dilate the cervix before true labor occurs. Click herefor an explanation of the differences between practice and true labor contractions.
The Dilation of the Cervix
The dilation of the cervix generally occurs after the onset of true labor, owing to the pulling motions of uterine contractions. The uterus acts as a large bag of extremely powerful muscles, and the cervix, its generally-closed neck, is opened by the movement of contractions pulling its outer rims upward.
Dilation is the longest phase of labor, and may last anywhere from two hours to a few days. On average, a first-time mother will labor for fourteen or fifteen hours, and a mother who has given birth before will experience dilation for six or seven. For most women, the process of dilating the cervix becomes increasingly uncomfortable as the labor progresses, owing to the strain of uterine muscles as they struggle to open the cervix.
In general, the cervix becomes completely dilated at about ten centimeters, or roughly for inches. The muscles of the uterus are at this point working very hard to keep the cervix fully opened. A woman does not generally feel a need to push until her cervix has been fully dilated by the contractions of her uterus, and the baby can not usually fit through the opening of the cervix until it has been fully dilated.
Pushing
The contractions of the uterus that dilate the cervix during labor also carry muscle tissue to the top of the womb. At about the time that the cervix becomes fully dilated, this muscle tissue has collected and has formed a piston-like, strong mass that is capable of pushing the baby outward. The process of pushing the baby outward is much shorter than the amount of time required to dilate the cervix, and may take from half an hour to three hours or more.
The contractions of the uterus continue during the pushing phase of labor, but they serve a different purpose. Instead of acting to pull the cervix open, they work to push the baby out of the cervix and through the vagina. Some women experience pushing contractions as relieving or even enjoyable, but others find them to be as agonizing as dilation contractions, if not more so.
During the pushing stage, women who have not had epidurals generally feel a very strong urge to push, and may experience severe pain if they do not (or can not, for whatever reason) give in to this urge. The baby is generally delivered after a few dozen pushing contractions.
The Delivery of the Baby and Placenta
Crowning is the term applied to the moment when a baby's head begins to show through the vagina. This is an exciting moment for everyone involved because it is an exhilerating reminder that labor is almost over. Labor may take only a few more contractions before the baby is out. Sometimes, a baby's head may disappear in between contractions, but this does not mean that the work being done during pushing contraction was futile.
During an emergency, a doctor or midwife may use forceps or a vacuum extractor to pull the baby out, but a woman's body is generally fully capable of accomplishing this task without assistance. The baby generally comes out gently--for the baby, at least. Mild to moderate bruising or tearing of vaginal and perineal tissue are common during the final delivery stages, but they do not always occur and most women recover from these problems quickly.
After the baby is out, the placenta, the baby's food source attached to its belly by the umbilical cord, follows shortly after, but this may take up to forty-five minutes. Heavy bleeding will usually occur until the placenta is expelled, because it contains anticoagulants, or compounds that inhibit blood clotting.
Childbirth is a thrilling, yet terrifying experience for most expectant mothers, and it doesn't take a rocket scientist (or an obstetrican, or a midwife) to understand the basics of how it works. With a little additional knowledge, most mothers will find that they can enter labor with the confidence and sense of security they deserve.