cord knots or prolapse, maternal seizures including eclampsia and epilepsy, application of a fetal scalp electrode, impending birth, or maternal Valsalva maneuver. In one example, Ambia and colleagues (2017) described prolonged decelerations lasting 2 to 10 minutes following an eclamptic seizure.
he placenta is efective in resuscitating the fetus if the original insult does not recur immediately. Occasionally, such self-limited prolonged decelerations are followed by loss of beat-to-beat variability, baseline tachycardia, and even a period of late decelerations, all of which resolve as the fetus recovers. Freeman and colleagues (2003) emphasize that the fetus may die during prolonged decelerations. hus, management of prolonged decelerations can be extremely tenuous. Management of isolated prolonged decelerations is based on bedside clinical judgment, which inevitably will sometimes be imperfect given the unpredictability of these decelerations.
Decelerations are virtually ubiquitous during the second stage of labor. In one study, only 1.4 percent of more than 7000 deliveries lacked decelerations during second-stage labor (Melchior, 1985). Both cord and fetal head compressions have been implicated as causes of decelerations and baseline bradycardia in this stage. Profound, prolonged fetal heart rate deceleration in the 10 minutes preceding vaginal delivery has been described (Boehm, 1975). And, similar prolonged second-stage decelerations were associated with a stillbirth and neonatal death (Herbert, 1981). hese experiences attest to the unpredictability of the fetal heart rate during second-stage labor.
Spong and associates (1998) analyzed the characteristics of second-stage variable fetal heart rate decelerations in 250 deliveries. hey found that as the total number of decelerations <70 bpm increased, the 5-minute Apgar score decreased. Of other patterns in second-stage labor, Picquard and coworkers (1988) reported that loss of beat-to-beat variability and baseline fetal heart rate < 90 bpm predicted fetal acidemia. Krebs and associates (1981) also found that persistent or progressive baseline bradycardia or baseline tachycardia was associated with lower Apgar scores. Gull and colleagues (1996) observed that abrupt fetal heart rate deceleration to < 100 bpm associated with loss of beat-to-beat variability for 4 minutes or longer was predictive of fetal acidemia. Thus, abnormal baseline heart rate-either bradycardia or tachycardia, absent beat-tobeat variability, or both-in the presence of deep second-stage decelerations is associated with a greater risk for fetal compromise (Fig.
With this approach, women with low-risk pregnancies are monitored for a short time on admission for labor. In one study, 3752 low-risk women in spontaneous labor at admission were randomly assigned either to auscultation of the fetal heart or to 20 minutes of electronic fetal monitoring (Mires, 2001). Use of admission electronic fetal monitoring did not improve neonatal outcome. Moreover, its use resulted in a greater number of interventions, including operative delivery. A similar study echoed these neonatal outcomes (Impey, 2003). More than half of the women enrolled in these studies eventually required continuous monitoring. A review by Devane and associates (2017) found that admission fetal monitoring programs for low-risk pregnancy are associated with a higher risk for cesarean delivery. Somewhat related, with the increasing rate of scheduled cesarean deliveries in the United States, clinicians and hospitals must decide whether fetal monitoring is required before the procedure in low-risk women.