Descent of the leading edge of the presenting part to the level of the ischial spines (0 station) is deined as engagement. A higher station at the onset of labor is signiicantly linked with subsequent dystocia (Friedman, 1965, 1976; Handa, 1993). Roshanfekr and associates (1999) analyzed fetal station in 803 nulliparas at term in active labor. At admission, the third with the fetal head at or below 0 station had a 5-percent cesarean delivery rate. This compared with a 14-percent rate for those with higher stations. The prognosis for dystocia, however, was not related to incrementally higher fetal head stations above the pelvic midplane (0 station). Importantly, 86 percent of nulliparous women without fetal head engagement at diagnosis of active labor delivered vaginally. These observations apply especially for parous women because the head typically descends later in labor.
Various labor factors have been implicated as causes of uterine dysfunction. As described, neuraxial analgesia can slow labor and has been associated with lengthening both first and second stages of labor and slowing the rate of fetal descent.
Chorioamnionitis is associated with prolonged labor, and some clinicians have suggested that this maternal intrapartum infection itself contributes to abnormal uterine activity. Satin and coworkers (I992) studied the efects of chorioamnionitis on oxytocin stimulation in 266 pregnancies. Infection diagnosed late in labor was found to be a marker of cesarean delivery performed for dystocia. Speciically, 40 percent of women developing chorioamnionitis after requiring oxytocin for dysfunctional labor later required cesarean delivery for dystocia. However, this was not a marker in women diagnosed as having chorioamnionitis early in labor. It is likely that uterine infection in this clinical setting is a consequence of dysfunctional, prolonged labor rather than a cause of dystocia.
Membrane rupture at term without spontaneous uterine contractions complicates approximately 8 percent of pregnancies. In the past, labor stimulation was initiated if contractions did not begin ater 6 to 12 hours. Practice-changing research included that of Hannah (1996) and Peleg (1999) and their associates, who enrolled a total of 5042 pregnancies with ruptured membranes in a randomized investigation. They measured the efects of induction versus expectant management and also compared induction using intravenous oxytocin with that using prostaglandin E2 gel. There were approximately 1200 pregnancies in each of the four study arms. They concluded that labor induction with intravenous oxytocin was preferred management. This was based on signiicantly fewer intrapartum and postpartum infections in women whose labor was induced. There were no signiicant differences in cesarean delivery rates. Subsequent analysis by Hannah and coworkers (2000) indicated higher rates of adverse outcomes when expectant management at home was compared with in-hospital observation. Mozurkewich and associates (2009) reported lower rates of chorioamnionitis, metritis, and neonatal intensive care unit admissions for women with term ruptured membranes whose labors were induced compared with those managed expectantly. At Parkland Hospital, labor is induced soon ater admission when ruptured membranes are confirmed at term. In those with hypotonic contractions or with advanced cervical dilation, oxytocin is selected to lower potential hyperstimulation risk. In those with an unfavorable cervix and no or few contraction, prostaglandin E\ (misoprostol) is chosen to promote cervical ripening and contractions. he beneit of prophylactic antibiotics in women with ruptured membranes before labor at term is unclear (Passos, 2012). However, in those with membranes ruptured longer than 18 hours, antibiotics are instituted for group B streptococcal infection prophylaxis (Chap. 64, p. 1221).