It is possible that prolonged first-stage labor presages that with the second stage. Nelson and associates (20l3) studied the relationships between the lengths of the irst and second stages of labor in 12,523 nulliparas at term delivered at Parkland Hospital. The second stage signiicantly lengthened concomitantly with increasing irst-stage duration. The 95th percentile was 15.6 and 2.9 hours for the first and second stages, respectively. Women with first stages lasting longer than 15.6 hours (>95th percentile) had a 16-percent rate of second-stage labor lasting 3 hours (95th percentile). his compared with a 4.5-percent rate of prolonged second stages in women with irst-stage labors lasting <95th percentile.
With ull cervical dilation, most women cannot resist the urge to "bear down" or "push" each time the uterus contracts (Chap. 22, p. 438). he combined force created by contractions of the uterus and abdominal musculature propels the fetus downward. At times, force created by abdominal musculature is compromised suiciently to slow or even prevent spontaneous vaginal delivery. Heavy sedation or regional analgesia may reduce the reflex urge to push and may impair the ability to contract abdominal muscles efectively. In other instances, the inherent urge to push is overridden by the intense pain created by bearing down. Two approaches to second-stage pushing in women with epidural analgesia have yielded contradictory results. The irst advocates pushing forcefully with contractions ater complete dilation, regardless of the urge to push. With the second, analgesia inusion is stopped and pushing begins only ater the woman regains the sensory urge to bear down. Fraser and coworkers (2000) found that delayed pushing reduced diicult operative deliveries, whereas Manyonda and associates (1990) reported the opposite. Hansen and colleagues (2002) randomly assigned 252 women with epidural analgesia to one of the two approaches. No adverse maternal or neonatal outcomes were linked to delayed pushing despite signiicantly prolonging second-stage labor. Plunkett and coworkers (2003), in a similar study, confirmed these indings.
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. hese 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.