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A membrane sweep is a labor stimulation technique used by midwives and obstetricians after 38 weeks of pregnancy. The outer membrane of the amniotic sac is manually separated from the cervix, often beginning labor within two days. It is usually the first step in labor stimulation before medications are used to induce labor. Stimulating the cervix this way releases prostaglandins, a lipid messenger molecule responsible for the contraction and relaxation of the smooth uterine muscle during labor.
An exam of the cervix is done before the membrane sweep. If a cervix is unripe, or has not begun to soften and efface, progressive labor is less likely to start after the procedure. A cervix that is still high and firm would indicate that the membrane sweep should be delayed.
After the cervix is determined to be in a favorable state for labor stimulation, the doctor will begin to insert one finger into the cervix. If the cervix is soft but still tightly closed, it may take a minute or two of gentle manipulation for the cervix to dilate enough to allow the finger to enter. Once the doctor is able to insert his finger through the neck of the cervix and into the uterus, he will use his finger to separate the amniotic sac containing the baby from the uterus wall.
A membrane sweep may initially cause some uterine irritability, resulting in irregular contractions. These contractions will not cause any dilation or effacement of the cervix. The contractions should eventually become regular and effective, signaling that labor is beginning.
The mucus plug will likely be dislodged during the membrane sweep. It is often bloody, but this is to be expected as the cervix dilates and softens. Cramping and intermittent spotting may begin after the procedure. Regular labor contractions should begin within 48 hours.
If the membrane sweep has not stimulated labor contractions, the procedure may be repeated. Stripping the membrane may be done two or three times before labor begins. This labor stimulating technique occasionally does not produce any favorable results, and a drug-induced labor may be recommended for the overdue mother.
Complications from the membrane sweep include an infection risk and a possible early rupture of the amniotic sac. If an expectant mother tests positive for group B strep (GBS), it is unlikely that the membrane will be stripped to begin labor. Infection may result when microbes travel from the vagina and cervix into the uterus when the cervix is manipulated. The amniotic membrane sac may be accidentally ruptured during the membrane sweep. If the amniotic sac ruptures, the mother will likely be admitted into the hospital for delivery because it is not safe for pregnancy to continue with a ruptured amniotic sac for more than 24 hours.