The first stage of labor involves cervical dilation, where the cervix opens from closed to ten centimeters to allow the baby to pass through. While this progression is generally continuous, the final stages can present a mechanical challenge. This is where the concept of a cervical lip becomes relevant, representing a temporary hurdle before the pushing phase of labor.
Defining a Cervical Lip
A cervical lip is a small, remaining rim of cervical tissue that has not yet fully dilated. It is the last portion of the cervix that needs to be drawn up and over the baby’s presenting part, usually the head. This tissue feels like a thin crescent or a palpable edge upon vaginal examination and is often observed when dilation reaches 9 to 9.5 centimeters.
The anterior lip, positioned toward the mother’s pubic bone, is the most frequent location for the remaining tissue. The posterior section of the cervix usually thins and retracts first, making a posterior lip less common.
Why the Cervical Lip Forms
The formation of a cervical lip results from mechanical forces, specifically how the baby’s head interacts with the cervix and the pelvis. Dilation occurs when the strong muscle fibers of the upper uterus contract, pulling the softer cervical tissue upward and around the baby’s head.
A lip forms when this retraction is uneven, often because the baby’s head is not pressing uniformly on the cervix. For example, a baby in an occiput posterior position (head toward the mother’s back) creates an asymmetrical pressure gradient. This malpositioning causes dilation to happen elliptically rather than in a perfect circle, leaving a small edge of the cervix unretracted.
How a Cervical Lip Affects Labor
The presence of a cervical lip can slow or stall labor right before full dilation. When a provider detects this tissue, the laboring person is asked to resist the urge to push, even if the sensation is strong. Pushing before the cervix is fully retracted can trap the lip between the baby’s head and the pelvic bone, leading to swelling and potential trauma. Pushing against the lip can also cause intense, localized pain, often described as a sharp sensation above the pubic bone.
Interventions to Resolve the Cervical Lip
Resolving a cervical lip focuses on encouraging the final piece of tissue to retract fully. Positional changes are one of the most effective methods used. Encouraging movement, such as side-lying, hands-and-knees, or leaning forward, can help shift the baby’s position slightly. This shift redistributes pressure on the cervix, allowing the lip to be pulled up during subsequent contractions.
Care providers may recommend “laboring down,” which involves waiting for the lip to resolve on its own with continued contractions. If the lip is persistent or the laboring person has a difficult-to-resist urge to push, a manual reduction may be attempted. This procedure involves the provider inserting fingers during a contraction and gently pushing the rim of tissue up and over the baby’s head.
Manual reduction is often a quick way to achieve full dilation. If the lip is significantly swollen, supportive measures like applying ice or encouraging a different position may be used to reduce the swelling before attempting manual reduction.