During the first stage of labor, the cervix dilates (opens) from 0 to 10 centimeters (cm). This stage has an early, or latent, phase, an active phase, and a transitional phase. The latent phase usually lasts the longest and is the least intense phase of labor. This phase is characterized by dilatation (opening) of the cervix to 3–4 cm along with the thinning out of the cervix (effacement). It can take place over a period of days without being noticed or over a period of two to six hours with distinctive contractions. Most women are relatively comfortable during the latent phase, and walking around is encouraged, since it naturally stimulates the process.
With the initiation of labor, the muscular wall of the uterus begins to contract causing the cervix to open (dilatation) and thin out (efface). For a first-time mother the cervix must completely efface before dilatation continues. Effacement is reported in percentages as 50 percent or 100 percent, which is completely thinned out. The amniotic sac may or may not break during labor, and the birth attendant may rupture the bag with an amnio-hook, which looks a little like a large crochet hook. There is no pain involved with the breaking the bag of waters, although the contractions may intensify. During a contraction, the infant experiences pressure that pushes it against the cervix to assist with the dilatation. During this first phase, a woman's contractions typically increase in frequency and duration. Periodic vaginal exams are performed by the physician or nurse to determine progress. As pain and discomfort increase, however, the woman may be tempted to request pain medication. The administration of pain medication or anesthetics should be delayed until the active phase of labor begins, at which point the medication will not act to slow down or stop the labor.
The active phase of labor is usually shorter than the first, lasting an average of two to four hours. The contractions are more intense and accomplishing more in less time. They may be three to four minutes apart lasting 40–60 seconds even though the pattern may not be regular. During the active phase, dilatation continues to 7 cm. Relaxing between contractions is essential for coping because these contractions are more intense. Breathing exercises learned in childbirth classes can help the woman cope with the discomfort experienced during this phase. Pain medication offered at this point consists of either a short-term medication, such as Nubain or Stadol, or long-term such as epidural anesthesia.
The transitional phase continues dilation 7–10 cm. It is the most exhausting and demanding phase of labor. The contractions become very strong, are two to three minutes apart, and last 60–90 seconds. It may feel as if the contractions never stop, and there is no time to relax between them. Dilatation of the final 3 cm to 10 cm takes, on average, 15 minutes to an hour. Strong rectal pressure, with or without an urge to push or move the bowels, may cause the woman to grunt involuntarily. If it is a natural labor and delivery, the laboring woman at this phase becomes very inwardly focused and can lose control. It is important to breathe with her through contractions as this keeps her attention on what she needs to do.