Sweeping Membranes—Any Drawbacks?
Abstract & Commentary
By John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert
Dr. Hobbins reports no financial relationship to this field of study.
Synopsis: Sweeping membranes may not accomplish its aim and could increase the chance of PROM.
Source: Hill MJ, et al. The effect of membranes sweeping on free labor rupture of membranes: a randomized controlled trial. Obstet Gynecol. 2008;111:1313-1319.
It has been common practice to "strip" or "sweep" membranes after 38 weeks to initiate spontaneous labor or, at least, to discourage patients from delivering after 42 weeks. Although the efficacy of this method has certainly not been overwhelmingly validated, studies have shown an increase in phospholipase A and prostaglandin F2 alpha, as well as an increase in uterine activity after membrane sweeping. An investigative group at Tripler Hospital in Honolulu noticed anecdotally that there appeared to be an increase in rupture of membranes prior to labor in patients having had their membranes swept. Therefore, they launched a study to see if there was such a relationship.
Hill et al1 randomized 300 patients with normal pregnancies who had reached 38 weeks to having their membranes swept (162) or not swept (138). The technique involved a 360 degree sweep of the membranes away from the lower uterine segment—if the cervix would admit a finger. If not, the cervix was "massaged." This was repeated weekly until the patient delivered. The control group had weekly visits but no sweeping. Those managing and delivering the patients were blinded as to which patients had what done.
Although there was a trend toward higher rate of pre-labor rupture of membranes in the swept group (12% vs 7%), it did not attain statistical significance (p = 0.19). However, if the cervix was dilated to more than 1 cm, there was a significant difference (9.1% vs 0%; p = 0.05) in membrane rupture before labor ensued.
It is of note that there were no differences between groups regarding the incidence of post term pregnancy, going 41 weeks or longer, spontaneous labor, or average gestational age at delivery.
Commentary
The authors concluded that if the patient was dilated to more than 1 cm (presumably, in those where the clinicians could "sweep" and not "massage"), there was an increase in premature rupture of the membranes. However, interestingly, the membranes sweeping maneuver did not accomplish in this small study what it was designed to do—patients in labor and/or preventing them from extending their pregnancies past 41 weeks.
A few years ago we set out to see if bacteria residing in the vagina were able to get a free ride upward through the cervix by uterine contractions occurring late in pregnancy ("in suck" theory). We recruited patients in late pregnancy to have extended transvaginal ultrasound investigations after a sterile echogenic material was inserted into their posterior fornices. The idea was that we could track the journey of the medium (and, therefore, bacteria) through the cervical canal. At the end of the observation period, one patient, who happened to be a nurse midwife, was scheduled to have her membranes stripped (our term), so we and she decided to see where the echogenic material would go after this procedure. Much to our surprise, we immediately could trace the ultrasound- opaque medium well up into the lower uterine segment—substantially further than the sweeping finger could reach.
In a few study patients we did note the presence of some contrast material in the upper cervical canal, but, obviously, if one is looking to catapult bacteria far up into the uterus, try membrane sweeping.
References
- Hill MJ, et al. The effect of membranes sweeping on free labor rupture of membranes: a randomized controlled trial. Obstet Gynecol. 2008;111: 1313-1319.
- McColgin SW, et al. Parturitional factors associated with membrane stripping. Am J Obstet Gynecol. 1993; 169:71-77.
- Keirse M, et al. Chronic stimulation of uterine prostaglandin synthesis during cervical ripening before the onset of labor. Prostaglandins. 1983;25:671-682.
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