Cervical dilation is the process by which the cervix opens, measured from zero to ten centimeters, allowing the baby to pass through the birth canal. During pregnancy, the cervix is closed, but uterine contractions facilitate its softening and widening as labor begins. This process is divided into stages, starting with the slow, latent phase of early dilation. It culminates in the active phase, where dilation progresses more quickly toward the full ten centimeters required for delivery.
When Lack of Dilation Becomes a Medical Concern
When cervical dilation slows or stops during the active phase of labor, healthcare providers may diagnose a condition known as labor dystocia, or “Failure to Progress.” This diagnosis is not applied to the early, latent phase, which can naturally be long and unpredictable. The active phase of labor is considered to begin when the cervix has dilated to six centimeters, the point where progression is expected to accelerate.
A diagnosis of labor arrest is reserved for circumstances where labor has stalled despite adequate uterine activity. Modern guidelines suggest that a Cesarean delivery for arrested labor should only be considered when the birthing person is at six centimeters dilation or more, has ruptured membranes, and shows no cervical change after four hours of strong contractions. If contractions are not strong enough, the time limit for no cervical change is extended to at least six hours while receiving medication to strengthen them.
Factors That Prevent Cervical Dilation
The failure of the cervix to dilate during the active phase of labor is often categorized by problems related to three main factors: the power, the passage, and the passenger. The “power” refers to the uterine contractions, which may be too weak, too short, or poorly coordinated to apply the pressure needed to open the cervix. For effective cervical dilation and fetal descent, contractions must generate adequate pressure and frequency.
The “passenger” refers to the fetus, where issues with size or positioning can impede progress. A baby that is too large (macrosomia) or one presenting in an unfavorable position, such as shoulder or brow first, may physically obstruct descent and prevent dilation.
The third factor, the “passage,” involves the mother’s pelvis and soft tissues, which must be adequate to accommodate the baby. If the maternal pelvis is too small or its shape is not conducive to the baby’s passage, a condition known as cephalopelvic disproportion, labor will stall mechanically.
Medical Strategies to Encourage Labor Progression
When dilation stalls, medical teams employ various strategies to encourage the progression of labor before resorting to surgical delivery. One common intervention is the use of synthetic oxytocin, often administered intravenously (Pitocin), which mimics the body’s natural hormone to stimulate contractions. This medication is carefully titrated to increase the frequency and intensity of uterine contractions, aiming for an optimal pattern that facilitates further dilation.
Another method is an amniotomy, which involves a healthcare provider artificially rupturing the amniotic sac, or “breaking the water,” using a small, sterile hook. Releasing the amniotic fluid can cause the baby’s head to move down and press more firmly against the cervix, often increasing the strength of contractions and speeding up labor.
Supportive measures are also routinely used, including encouraging the birthing person to change positions, such as walking, squatting, or lying on a different side. Changing positions can sometimes help shift the baby into a more favorable position, resolving the underlying issue of labor dystocia.
The Necessary Role of Cesarean Delivery
If the lack of dilation persists despite medical augmentation efforts, or if complications arise, a Cesarean section (C-section) becomes a necessary intervention. Failure to progress is a leading reason for C-sections, especially for first-time mothers. Prolonged labor increases the risks of infection for both the mother and the baby, and can lead to severe maternal fatigue. A stalled labor can also result in fetal distress, indicated by an abnormal heart rate. When these risks outweigh the benefits of continued vaginal delivery, the C-section is performed to safely remove the baby, serving as the definitive resolution to labor arrest.