A membrane sweep, sometimes called “stripping the membranes,” is a manual technique offered late in pregnancy, usually after 39 weeks, to encourage the natural start of labor and potentially avoid medical induction. The goal is to stimulate the body’s natural processes that lead to contractions and cervical change.
The procedure is performed during a standard vaginal examination. The provider inserts gloved fingers through the cervix and uses a circular motion to gently separate the amniotic sac from the lower wall of the uterus. This action gives the procedure its name and is generally quick, though some patients find it uncomfortable.
This physical separation triggers a local release of natural hormones called prostaglandins. Prostaglandins are used in medical induction because they help the cervix soften, thin out (efface), and begin to open (dilate). By stimulating this release, the sweep attempts to kickstart the physiological cascade leading to labor.
Dilation Criteria and Cervical Readiness
Some degree of dilation is required for a membrane sweep, but it is not the only factor. The cervix must be open enough for the provider to insert a finger and physically access the membranes to perform the sweeping motion. A minimum of 1 to 2 centimeters of dilation is often necessary for this access, but the overall readiness of the cervix is a more important consideration.
The comprehensive assessment tool used by care providers to determine if a cervix is favorable for a sweep or for induction is the Bishop Score. This scoring system evaluates five different parameters of the cervix and the baby’s position, with dilation being only one component. The other factors include effacement (thinning), consistency (soft or firm), position (anterior or posterior), and the baby’s station in the pelvis.
A higher Bishop Score indicates a greater likelihood that a sweep will be successful in promoting labor. A score greater than 7 is generally considered a “ripe” or favorable cervix, meaning the tissue is already preparing for labor. If the cervix is determined to be hard and closed, or “unfavorable,” a membrane sweep is often not possible or beneficial. The overall Bishop Score is the primary guide to cervical readiness.
Efficacy, Side Effects, and Next Steps
A membrane sweep is a method of encouraging labor that works for some but is not guaranteed to initiate contractions immediately. Research suggests that undergoing a sweep makes spontaneous labor within 48 hours more likely compared to having no intervention. For instance, without a sweep, approximately 6 out of 10 people might go into labor, but with a sweep, that number increases to just over 7 out of 10.
The procedure is generally considered safe, but patients should expect some common side effects immediately afterward. It is normal to experience mild cramping, similar to menstrual discomfort, which can sometimes be confused with the very early stages of contractions.
Light vaginal spotting or bleeding is also a frequent and expected side effect, as the cervix is highly vascular and the stimulation can cause minor vessel rupture.
The care provider will clearly distinguish these minor, expected side effects from reasons to seek immediate medical attention, such as heavy bleeding or the premature rupture of membranes. If the initial sweep is unsuccessful, the procedure may be offered again, often a week later, provided the cervix remains accessible.
If labor does not begin after one or more sweeps, the next step in the process involves discussing formal medical induction options with the care team, which typically use medication or other techniques to achieve delivery.