BACKGROUND: Routine sweeping or “stripping” of the membranes beginning at 38 to 40 weeks’ gestation is an effective method of reducing the risk of a postdate and post-term pregnancy, as well as the need for more formal induction of labor. However, sweeping has not been shown to decrease the rate of cesarean delivery. This study is the first clinical trial of the effectiveness of membrane sweeping in conjunction with formal induction of labor.
POPULATION STUDIED: Nulliparous (N=130) and multiparous (N=118) women at term (38 to 42 weeks) were recruited into the study if they were admitted for induction of labor and had not had pre-admission sweeping performed. Indications for induction of labor included hypertension, intrauterine growth restriction, post-term, gestational diabetes, and oligohydramnios.
STUDY DESIGN AND VALIDITY: Pairs of eligible women were matched for parity and method of induction, and each was assigned to membrane sweeping or gentle cervical examination to determine Bishop score before induction. Sweeping involved separating the membranes from the lower uterine segment as far as possible with a finger inserted into the internal os. Induction protocols included the use of 3 mg vaginal prostaglandin (PGE2) pessary for women with unfavorable cervices (Bishop score <5) and rupture of membranes at any point when the cervix was favorable. PGE2 was repeated every 6 hours if needed. Oxytocin was started if there were insufficient uterine contractions within 3 hours after rupture of membranes. The oxytocin protocol called for increases of 2.5 mU per minute every half hour to a maximum of 40 mU per minute to achieve 4 to 5 contractions every 10 minutes. Vaginal examinations were routinely done every 3 hours.
OUTCOMES MEASURED: Induction-to-delivery interval, total duration of labor, maximum dose of oxytocin used during induction, and mode of delivery were the primary maternal outcomes reported. The authors also reported meconium-stained amniotic fluid and admission to the neonatal unit but did not report any other patient-based outcomes, such as pain or satisfaction.
RESULTS: No differences in any outcome measures were found for multiparous women. Nulliparous women assigned to the membrane sweeping group who required cervical ripening with prostaglandins had shorter induction-to-delivery intervals (13.6 vs 17.3 hours, P=.043), required less oxytocin, were more likely to have a spontaneous vaginal delivery (83.3% vs 58.2%, P=.01; number needed to treat [NNT]=4) and were less likely to require a cesarean delivery (6.3% vs 21.8%, P=.01; NNT=7). Nulliparas who had induction with artificial rupture of the membranes plus oxytocin also appeared to have shorter induction-to-delivery intervals and to require lower maximum doses of oxytocin. When these results were analyzed according to Bishop score, however, significant differences persisted only for nulliparous women who had scores of less than 5. There were no significant differences in other outcome measures.
Clinicians should offer membrane sweeping to nulliparous women with Bishop scores less than 5 who require induction of labor. The NNTs to avoid cesarean delivery (7) or operative vaginal delivery (4) are favorable, and the procedure carries little risk to the woman aside from discomfort. There does not appear to be an additional benefit of membrane sweeping in nulliparas with favorable cervices or in multiparous women regardless of their cervical examination results.