Although some intervention is indicated for prolonged pregnancies, the method and timing of this are not unanimous. he decision focuses on whether labor induction is warranted or if expectant management with fetal surveillance is best. In a survey done more than 10 years ago, Cleary-Goldman and associates (2006) reported that 73 percent of members of the American College ofObstetricians and Gynecologists routinely induced women at 41 weeks. Most of the remainder performed twice weekly fetal testing until 42 weeks.
Although all obstetricians know what an "unfavorable cervix" is, the term unfortunately defies precise objective deinition. Thus, investigators have used difering criteria for studies of prolonged pregnancies. Harris and coworkers (1983) defin�d an unfavorable cervix by a Bishop score <7 and reported thiS m 92 percent of women at 42 weeks (Chap. 26, p. 505). Hannah and colleagues (1992) found that 40 percent of 3407 women with a 41-week pregnancy had an "undilated cervix." In a study of 800 women undergoing induction for postterm pregnancy at Parkland Hospital, Alexander and associates (2000b) reported that women in whom there was no cervical dilation had a twofold higher cesarean delivery rate fore" dystocia. " Yang and coworkers (2004) found that cervical length 53 em measured with transvaginal sonography was predictive of successful induction. In a similar study, Vankayalapati and associates (2008) found that cervical length 525 mm was predictive of spontaneous labor or successful induction.
Several investigators have evaluated prostaglandin E2 (PGE2) and E1 (PGE1) for induction in women with an unfavorable cervix and prolonged pregnancies. A study by the MaternalFetal Medicine Units Network (1994) found that PGE2 gel was not more efective than placebo. Alexander and associates (2000c) treated 393 women with a postterm pregnancy with PGE2, regardless of cervical "favorability," and reported that almost half of the 84 women with cervical dilatation of 2 to 4 em entered labor with PGE2 use alone. In another study, mifepristone was reported to increase uterine activity without uterotonic agents in women beyond 41 weeks (Fasset, 2008). Prostaglandins and other agents used for cervical ripening are discussed in Chapter 26 (p. 506).
Sweeping or stripping of the membranes to induce labor and thereby prevent postterm pregnancy was studied in 15 randomized trials during the 1990s. Boulvain and coworkers (2005) performed a metaanalysis of these and found that membrane stripping at 38 to 40 weeks lowered the frequency of postterm pregnancy. Although maternal and neonatal infection rates were not increased, this practice did not modiy the cesarean delivery rate. Since then, randomized trials by Wong (2002), Kashanian (2006), Hill (2008), and their coworkers found that sweeping membranes did notereduce the need to induce labor.
Drawbacks of membrane stripping included pain, vaginal bleeding, and irregular contractions without labor.
The station of the fetal head within the pelvis is another predictor of successful postterm pregnancy induction. Shin and colleagues (2004) studied 484 nulliparas who underwent induction after 41 weeks. The cesarean delivery rate was directly related to station. The rate was 6 percent if the vertex before induction was at -1 station; 20 percent at -2 station; 43 percent at -3 station; and 77 percent at -4 station.