What does it mean to "strip membranes" in pregnancy?

Encourage Labor. Your doctor may strip the membranes if you are at or past your due date to encourage labor. If the cervix has started to dilate, the doctor can slip his or her finger between the cervix and the membranes with a sweeping circular motion going all around the cervix. This releases prostaglandins and may result in cramping or the onset of contractions.
Vigorous cervix exam. In the last couple of weeks of pregnancy when your cervix is dilated your doctor can sweep a finger in the space between the cervix and the amniotic membranes. This releases a chemical called prostaglandins which can stimulate contractions. Stripping the membranes is thought to help people go into labor sooner.
Induction method. While your doctor or midwife is checking your cervical dilation at the end of your pregnancy, they can sweep their finger in a circle to slightly loosen the bag of water from the top of the cervix. This "membrane stripping" can release a hormone called prostaglandin that may help to induce labor if your body is ready. Spotting and some cramping is common after this exam.