Because of the marginal benefits from induction with an unfavorable cervix, as just discussed, some clinicians prefer instead to implement a strategy of fetal testing beginning at 41 completed weeks. For example, in a Canadian study, 3407 women were randomly assigned at 41 or more weeks to induction or to fetal testing (Hannah, 1992). In the surveillance group, evaluation included: (1) counting fetal movements during a 2-hour period each day, (2) nons tress testing three times weekly, and (3) amnionic fluid volume assessment two to three times weekly, with pockets <3 em considered abnormal. Labor induction resulted in a small but signiicant reduction in the cesarean delivery rate compared with fetal testing-2e1 versus 24 percent, respectively. This diference was due to fewer procedures for fetal distress. here were only two stillbirths in the fetal testing group.
The !v1aternal-Fetal Medicine Network performed a randomized trial of induction versus fetal testing beginning at 41 weeks (Gardner, 1996). Fetal surveillance included nonstress testing and sonographic estimation of amnionic fluid volume performed twice weekly in 175 women. Perinatal outcomes were compared with those of 265 women also at 41 weeks randomly assigned to induction with or without cervical ripening. There were no perinatal deaths, and the cesarean delivery rate was not diferent between management groups. he results of this study could be used to support the validity of either management scheme.
In an analysis of 22 trials, Gulmezoglu and colleagues (2012) found that induction after 41 weeks rather than surveillance was associated with significantly fewer perinatal deaths and meconium aspiration syndrome cases and a lower cesarean delivery rate. In a review of two metaanalyses and a randomized study, similar conclusions were reached (Mozurkewich, 2009).
In most studies, labor induction at 42°/7 weeks has a higher cesarean delivery rate compared with spontaneous labor. From Parkland Hospital, Alexander and coworkers (2001) evaluated pregnancy outcomes in 638 such women in whom labor was induced and compared them with outcomes of 687 women with postterm pregnancies who had spontaneous labor. Cesarean delivery rates were signiicantly increased-19 versus 14 percent-in the induced group because of failure to progress. When these investigators corrected for risk factors, however, they concluded that intrinsic maternal factors, rather than the induction itself, led to the higher rate. These factors included nulliparity, an unfavorable cervix, and epidural analgesia.
A large study from Denmark by Zizzo and associates (20e17) is also instructive. In 2011e, the Danish national guidelines were changed from labor induction at 42°/7 weeks with no fetal sur veillance to labor induction at 41e/7 to 416/7 weeks with fetal surveillance beginning at 41°/7 weeks. They compared two 3-year epochs-one before and one ater 20 II-and the results are shown in Table 43-2. The rate of pregnancies that progressed past 42°/7 weeks decreased from 2.85 to 0.62 percent. Concu�rently, as expected, the induction rate rose signiicantly, and thiS was accompanied by a drop in the perinatal mortality rate-22 to 13 per 1000 births. The cesarean delivery rate was not changed. A similar before-and-ater observational study reported that induction at ::42 weeks was associated with a signiicantly lower cesarean delivery rate-15 versus 19.4 percent (Bleicher, 2017).
From the foregoing, evidence to substantiate interventionwhether induction or fetal testing-commencing at 41 versus 42 weeks is limited. Most evidence used to justiy intervention
TABLE 43-2. National Death Cohort Study of 102,1e67 Pregnancies that Reached 41e°/7 Weeks' Gestation