For labor induction, artificial rupture of the membranessometimes called surgical induction-can be used and always implies a commitment to delivery. The main disadvantage of amniotomy used alone for labor induction is the unpredictable and occasionally long interval until labor onset. hat said, in a randomized trial, Bakos and Backstrom (1987) found that amniotomy alone or combined with oxytocin was superior to oxytocin alone. Mercer and colleagues (1995) randomly assigned 209 women undergoing oxytocin induction to either early amniotomy at 1 to 2 cm or late amniotomy at 5 cm. Early amniotomy was associated with a 4-hour reduction in labor duration. With early amniotomy, however, the incidence of chorioamnionitis was elevated.
For labor augmentation, amniotomy is commonly performed when labor is abnormally slow. Rouse and associates (1994) found that amniotomy with oxytocin augmentation for arrested active-phase labor shortened the time to delivery by 44 minutes compared with that of oxytocin alone. Although amniotomy did not alter the delivery route, one drawback was that it significantly increased the incidence of chorioamnionitis.
Regardless of the indication, amniotomy is associated with a risk of cord prolapse. To minimize this risk, disengagement of the fetal head during amniotomy is avoided. Toward this goal, fundal or suprapubic pressure or both may be helpful. Some clinicians prefer to rupture membranes during a contraction. If the vertex is not well applied to the lower uterine segment, aNo effect on overall rate; cesarean delivery for fetal distress significantly increased. blncreased mild and moderate umbilical cord compression patterns.
NA = not assessed.
a gradual egress of amnionic fluid can sometimes be accomplished by several membrane punctures with a 26-gauge needle held with a ring forceps and with direct visualization using a vaginal speculum. In many of these, however, membranes tear and luid is lost rapidly. Because of the risk of cord prolapse or rarely abruption, the fetal heart rate is assessed before and immediately after amniotomy.
Labor induction by membrane "stripping" is a frequent practice. Several studies have suggested that membrane stripping is safe and lowers the incidence of postterm pregnancy without consistently raising the incidence of ruptured membranes, infection, or bleeding. Authors of one large metaanalysis found that membrane stripping reduced the number of women remaining undelivered after 41 weeks without elevating the infection risk. They concluded that eight women would need to undergo membrane stripping to avoid one labor induction. Downsides are discomfort and associated bleeding (Boulvain, 2005).
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