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During the first stage of labor, the contractions of the uterus will cause the cervix to efface and dilate.

Effacement refers to the shortening and thinning of the cervix. This is expressed as a percentage, from 0% (long and thick) to 100% (completely thinned out).

Dilation, or dilatation, refers to the opening of the cervix. This is expressed in centimeters, 0 (closed) to 10 (complete dilation).

Station is another term used to indicate the progress of labor, and it refers to the position of the baby’s “presenting part” in relation to the ischial spines in the pelvis. A zero station means the presenting part (usually the baby’s head) is level with the spines. A minus number refers to the number of centimeters the baby’s head is above the spines, and a plus number refers to the number of centimeters the baby’s head is below the spines. The head is usually considered to be engaged when it reaches the level of the ischial spines.

Your progress in labor is determined by vaginal examinations, which measure the effacement and dilation of the cervix and the station of the baby. Your physician, nurse midwife, and labor and delivery nurse will perform your examinations, helping you assess your progress in labor.
The first stage of labor is divided into three phases: early, active, and transition.

Early Phase

The early phase of labor extends from the onset of labor until the cervix is dilated approximately four centimeters. During this phase, the contractions are regular, every 5–10 minutes, and they usually last for about 30–45 seconds. They are usually of mild to moderate intensity.

The contractions result in the effacement of the cervix and dilation up to four centimeters. This process usually takes about six to twelve hours.

If you think you may be in labor, it is best to avoid eating solid foods. The intake of water, clear liquids, or ice chips is encouraged.

Generally, your labor will progress more rapidly and you will be more comfortable if you continue light activities such as walking.

During this phase, you may want to begin practicing the relaxation techniques you learned during your pregnancy. You may also wish to practice the breathing patterns during your contractions when other efforts are no longer effective. Your coach will help you by timing your contractions and by providing you with physical comfort and emotional support.

Active Phase

The active phase is when the cervix becomes four centimeters dilated, and contractions usually increase in intensity and become somewhat longer, lasting 45–60 seconds. The contractions then remain regular, usually two to five minutes apart.

During this stage, the cervix dilates at the rate of approximately one centimeter per hour for first pregnancies. For subsequent pregnancies, the process usually occurs more rapidly unless the baby is larger in size or is in an unusual position.

It is common to experience nausea or vomiting and trembling of the legs during the active phases. Your coach will continue to support you physically and emotionally.

Transition Phase

During the transition phase, the cervix goes from approximately eight centimeters dilation to complete dilation. It is the shortest but most intense part of labor. Contractions are usually every two to three minutes; they last 60–90 seconds and are very intense. As complete dilation approaches, you may develop pressure sensations in the rectum and an urge to push.

Nausea, vomiting, chills, tremors, difficulty in maintaining relaxation, and discouragement are also common during this phase. Your coach will continue with physical and emotional comfort measures.
You should not begin pushing down with the abdominal muscles until you are told to do so, since it could result in the tearing of the cervix.