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Obstetrics & Gynecology 2000;96:539-542
© 2000 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Membrane Sweeping in Conjunction With Labor Induction

L. C. FOONG, MD, K. VANAJA, MRACOG, G. TAN, MBBS and S. CHUA, PhD

From the Department of Obstetrics & Gynaecology, National University Hospital, Singapore.

Address reprint requests to: L. C. Foong, MD National University Hospital, Singapore Department of Obstetrics and Gynaecology 5 Lower Kent Ridge Road 119074 Singapore E-mail: obgflc{at}leonis.nus.edu.sg


   Abstract
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Abstract
Materials and Methods
 Results
 Discussion
 References
 
Objective: To determine whether cervical membrane sweeping (stripping) during induction of labor is beneficial.

Methods: We compared outcomes of labor after induction in pregnant women at term in a randomized trial. Women were assigned to having their membranes swept or not during induction. Outcome measures included duration of labor, maximum dose of oxytocin used, induction-labor interval, and mode of delivery.

Results: We recruited 130 nulliparas (64 sweep, 66 non-sweep) and 118 multiparas (60 sweep, 58 nonsweep). Among nulliparas who received intravaginal prostaglandin (PG) E2 and oxytocin, those who had simultaneous sweeping had significantly shorter mean (± standard error of mean) induction-labor interval (13.6 ± 1.4 versus 17.3 ± 1.2 hours, P = .048), lower mean maximum dose of oxytocin (6.8 ± 0.8 versus 10.35 ± 1.1 mU/minute, P = .01), and increased normal delivery rates (vaginal delivery 83.3% versus 58.2%, P = .01). Sweeping also had a favorable effect on nulliparas who received oxytocin alone (mean induction-labor interval 5.8 ± 3.1 versus 11.2 ± 3.6 hours, P = .04; mean maximum dose 8.8 ± 1.3 versus 16.3 ± 1.9 mU/min, P = .01). Those differences were limited to women with unfavorable cervices. There were no differences in any outcome measures in multiparous women.

Conclusion: Sweeping of the membranes during induction of labor had a beneficial effect on labor and delivery, which appeared to be limited to nulliparas with unfavorable cervices who needed cervical priming with PGE2.

Antenatal outpatient sweeping (or stripping) of membranes off the lower segment in pregnant women at term reduces the need for labor induction for post-term delivery when used alone1,2 or with vaginal prostaglandin (PG).3 Sweeping has been used since the 19th century,4 and although its exact mechanism is not fully understood, it is believed to stimulate the onset of spontaneous labor by increasing endogenous PG.5,6 It has few major adverse effects and does not appear to increase maternal and neonatal morbidity compared with normal delivery,1 unlike more established formal methods of induction that use PG or oxytocin. Therefore, it is often more acceptable to women who desire a more conservative approach to inducing post-term delivery.

Sweeping is believed to release endogenous PG,5 which ripens the cervix, leading to onset of labor through initiation of a self-perpetuating prostaglandin cascade.7 In theory, it should augment induction of labor, particularly when women have unfavorable cervices, because of the ripening effects of PG release and the synergistic uterotonic action of oxytocin.8 We did a systematic search using PubMed, MEDLINE, PreMEDLINE, HealthSTAR, and publisher-supplied citations from 1966 to January 2000. Search terms included "membrane," "sweeping," "stripping," "labor," and "induction." Although we found many reports on sweeping for induction or cervical ripening, we found none on whether sweeping concurrent with induction of labor affected induction outcome. The current study assessed the efficacy and value of sweeping membranes during formal induction of labor.


   Materials and Methods
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Abstract
 Materials and Methods
Results
 Discussion
 References
 
A randomized trial was done to compare outcomes of labor after induction at term. Women at term (38–42 weeks) were recruited upon admission for induction of labor. They were matched for parity and induction method, and each was assigned to membrane sweeping or not, during induction according to a computer-generated list of random binary numbers. The list was kept concealed and only the next number was displayed upon each allocation. Separate randomization lists were used depending on whether they were nulliparas or multiparas and whether oxytocin or PGE2 was used for the induction. None of the women had membrane sweeping before admission for induction of labor. In women randomly assigned to sweeping (study patients) the membranes were separated from the cervix and lower part of the uterus as far as possible with a finger inserted in the cervical os during vaginal examinations normally done during induction. Women randomly assigned to no sweeping (controls) had only gentle vaginal examinations to determine Bishop scores as scheduled. Indications for induction and demographic details of subject population are given in Table 1Go. All eligible women we approached for enrollment agreed to participate.


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  		Table 1. Characteristics of Subjects
 
Induction methods followed the protocol of the National University Hospital, Singapore. Nulliparas with unfavorable cervices (Bishop scores less than 5) had 3 mg PGE2 inserted to the posterior fornix with an additional 3-mg pessary inserted 6 hours later if there were no significant contractions and the cervix was dilated less than 3 cm. Another vaginal examination was done after 6 more hours. If a cervix was favorable during any examination, the membranes were ruptured and oxytocin infusion given, according to a set regimen, titrated against response to achieve 4 to 5 contractions every 10 minutes. The infusion comprised half-hourly increases in 2.5 mU/minute steps from a minimum of 2.5 mU/minute to a maximum of 40 mU/minute. If contractions occurred spontaneously, oxytocin was withheld unless progress was abnormal. Without contractions, oxytocin was given 3 hours after membrane rupture if there was insufficient progress. The same protocol was followed for multiparas except that the concentration of oxytocin was halved. Vaginal examinations were done at 3-hour intervals unless there were clinical indications to the contrary.

Outcome measures included duration of labor, maximum dose of oxytocin, interval between start of induction and onset of labor (induction-labor interval), and mode of delivery. The start of induction was defined as the time of insertion of the first prostaglandin pessary for women who needed priming and the time at which artificial rupture of membranes was done for those who did not. The onset of labor was defined as the onset of regular painful contractions more than once every 3 minutes that required analgesia. Student t test was used for analysis of parametric data, Mann-Whitney U test for nonparametric data, and Fisher exact test for analysis of delivery results and indications for induction. P < .05 in any test was considered statistically significant.


   Results
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Abstract
 Materials and Methods
 Results
Discussion
 References
 
We recruited 130 nulliparas (64 sweep, 66 nonsweep) and 118 multiparas (60 sweep, 58 nonsweep). Among nulliparas, 103 needed PGE2 (48 sweep, 55 nonsweep) and 27 (16 and 11, respectively) had their membranes ruptured and were given oxytocin at first examination. For multiparas, 62 needed PGE2 (27 and 35, respectively) and 56 had membranes ruptured and oxytocin (33 and 23, respectively). There were no significant differences between groups (Table 1Go). The mean (± standard error of the mean [SEM]) number of sweeps among nulliparas who had their membranes swept (priming) was 2.3 ± 0.1, nulliparas (artificial rupture of membranes + oxytocin) 1.1 ± 0.1, multiparas (priming) 2.2 ± 0.1, multiparas (artificial rupture of membranes + oxytocin) 1.1 ± 0.03.

Among nulliparas who needed initial cervical priming with intravaginal PG, those who had membrane sweeping had a shorter mean (±SEM) induction-labor interval (13.6 ± 1.4 versus 17.3 ± 1.2 hours, P = .048, Figure 1Go) and required less oxytocin (mean maximum dose 6.8 ± 0.8 versus 10.35 ± 1.1 mU/minute, P = .01, Figure 2Go) than those who were not swept. Swept women also had a significantly greater likelihood of better delivery outcome (vaginal delivery 40 of 48 [83.3%] versus 32 of 55 [58.2%] and cesarean delivery three of 48 [6.3%] versus 12 of 55 [21.8%], P = .01, Table 2Go). Nulliparas who needed only artificial rupture of membranes and oxytocin also had favorable outcomes if swept (mean induction-labor interval 5.8 ± 3.1 versus 11.2 ± 3.6 hours, P = .04; mean maximum dose 8.8 ± 1.3 versus 16.3 ± 1.9 mU/minute, P = .01). However, when results were analyzed according to Bishop scores, the differences persisted only in those with unfavorable cervices (Bishop scores under 5) (induction-labor interval 13.9 ± 1.4 versus 17.3 ± 1.2 hours, P = .039 and mean maximum dose of oxytocin 6.3 ± 0.9 versus 10.4 ± 1.2, P = .01). Data were tested for normality with the Kolmogorov-Smirnov test. The data on induction-labor interval were normally distributed, whereas the maximum dose of oxytocin was nonparametric. Student t test was used for analysis of the former and Mann-Whitney U test for the latter. There were no significant differences between groups in duration of labor. There were no significant differences in complications of labor, in meconium staining of liquor, or admissions to the neonatal unit (Table 1Go). Indications for cesarean deliveries are summarized in Table 3Go. Sweeping made no difference in indications for cesarean. There were no significant differences in any outcome measures in multiparas.



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  		Figure 1. Effect of membrane sweeping on induction-labor interval in nulliparas who needed prostaglandin E2. Lines indicate mean value.

 


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  		Figure 2. Effect of membrane sweeping on dose of oxytocin used in nulliparas who needed prostaglandin E2. Lines indicate mean value.

 

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  		Table 2. Delivery Mode
 

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  		Table 3. Indications for Cesarean
 

   Discussion
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Abstract
 Materials and Methods
 Results
 Discussion
References
 
Although sweeping the membranes has fewer adverse effects and is arguably more acceptable to women, it has less predictable results than formal methods of induction. Many studies showed that fewer women eventually required induction for post-term delivery if cervical sweeping was done antenatally.1 The current study showed that sweeping during vaginal examinations for induction of labor benefitted induction and labor by shorter induction-labor intervals, less need for oxytocin, and increased likelihood of normal delivery, but those benefits were limited to nulliparas, particularly those with unfavorable cervices at the start of induction.

Cervical sweeping likely involves release of endogenous PG. Amnion sweeping is known to release many substances (prostaglandins PGF2{alpha} and endocervical phospholipase A2) that soften the cervix,9 which might explain in part why sweeping has a more significant affect on nulliparas with unfavorable cervices, who would benefit most from cervical softening. Prostaglandin F2{alpha} also augments oxytocin-induced contractions,8 which might increase the efficacy of oxytocin and endogenous oxytocin spurts that occur after sweeping10 and vaginal examination (Ferguson’s reflex). That might explain the reduced need for oxytocin in women who had their membranes swept. It has been shown that increased uterine activity and PGF2{alpha} release in response to sweeping occurs rapidly5 and lasts for at least 6 hours.11 Vaginal examinations in the current study were done at 6-hour intervals during PGE2 priming, so concurrent sweeping might have prolonged the endogenous response to sweeping during induction, shortening the induction-labor interval.

Besides the shortened induction-labor interval, we found that sweeping significantly increased vaginal delivery rates, lowered cesarean rates, and possibly caused a synergistic effect when membrane sweeping was simultaneous with administration of intravaginal PGE2. That finding is supported by Doany and Mc-Carty,3 who showed that women who had weekly outpatient membrane stripping and intravaginal PGE2 gel had a significantly shortened median time to delivery compared with either method alone or placebo. They did not report any improvement in vaginal delivery rates, which might have been because most women who had PGE2 gel and membrane sweeping only had single sweeps antenatally. The effect might be enhanced if the procedure is done immediately before onset of labor, as in the current study. McColgin et al6 showed that there was a significant increase in uterine contractile activity immediately after membrane sweeping, which would support that. The levels of plasma PG after membranes sweeping alone6 were approximately one tenth those achieved during active labor,8 which might sufficiently augment labor and improve delivery outcome. However, the numbers in all those studies are relatively small, and only a larger trial would achieve the appropriate power to confirm the differences.


   Footnotes
 
PII S0029-7844(00)00995-9

Received December 1, 1999. Received in revised form May 22, 2000. Accepted June 15, 2000.


   References
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Abstract
 Materials and Methods
 Results
 Discussion
 References
 
1. Boulvain M, Irion O, Marcoux S, Fraser W. Sweeping of the membranes to prevent post-term pregnancy and to induce labor: A systematic review. Br J Obstet Gynaecol 1999;106:481–5.[Medline]

2. Allott HA, Palmer RP. Sweeping the membranes: A valid procedure in stimulating the onset of labor? Br J Obstet Gynaecol 1993;100:898–903.[Medline]

3. Doany W, McCarty J. Outpatient management of the uncomplicated postdate pregnancy with intravaginal prostaglandin E2 gel and membrane stripping. J Matern Fetal Med 1997;6:71–8.[Medline]

4. Thiery M, Baines CJ, Kierse MJ. The development of methods for inducing labor. In: Chalmers I, Enkin MW, Kierse MJ, eds. Effective care in pregnancy and childbirth Oxford, England: Oxford University Press, 1989:969–80.

5. Mitchell MD, Flint AP, Bibby J, Brunt J, Arnold JM, Anderson ABM, et al. Rapid increases in plasma prostaglandin concentrations after vaginal examination and amniotomy. BMJ 1977;2: 1183–5.

6. McColgin PG, Bennett WA, Roach H, Cowan BD, Martin JN, Morrison JC. Parturitional factors associated with membrane sweeping. Am J Obstet Gynecol 1993;169:71–7.[Medline]

7. Chez RA. Cervical ripening. Clin Obstet Gynecol 1998;41:606–10.[Medline]

8. Fuchs AR. Prostaglandin F2 alpha and oxytocin interactions in ovarian and uterine function. J Steroid Biochem 1987;27:1073–80.[Medline]

9. Takahashi T, Marcus B, Scheerer RG, Katz M. A new model for objective assessment of cervical ripening: The effect of prostaglandin E2 and prelabor contractility. Am J Obstet Gynecol 1991;164: 1115–8.[Medline]

10. Chard T, Gibbens GL. Spurt release of oxytocin during surgical induction of labor in women. Am J Obstet Gynecol 1983;147:678–80.[Medline]

11. Manabe Y, Yoshimura S, Mori T, Aso T. Plasma levels of 1314-dihydro-15-keto prostaglandin estrogens and progesterone F2{alpha} during stretch-induced labor at term. Prostaglandins 1985;30:141–52.[Medline]




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P. C. Tan, R. Jacob, and S. Z. Omar
Membrane sweeping at initiation of formal labor induction: a randomized controlled trial.
Obstet. Gynecol., March 1, 2006; 107(3): 569 - 577.
[Abstract] [Full Text] [PDF]

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