Fetal movements commonly produce heart rate decelerations. Timor-Tritsch and associates (1978) reported this during nonstress testing in half to two thirds of tracings, depending on the vigor of the fetal motion. This high incidence of decelerations inevitably makes interpretation of their signiicance problematic. Indeed, Meis and coworkers (1986) reported that variable fetal
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FIGURE 17-8 Nonreactive nonstress test (left side of tracing) followed by contraction stress test showing mild, late decelerations (right side of tracing). Cesarean delivery was performed, and the severely acidemic fetus could not be resuscitated.
heart rate decelerations during nonstress tests were not a sign of fetal compromise. he American College of Obstetricians and Gynecologists (2016) has concluded that variable decelerations, if nonrepetitive and brief-less than 30 seconds-do not indicate fetal compromise or the need for obstetrical intervention. In contrast, repetitive variable decelerations-at least three in 20 minutes-even if mild, have been associated with a greater risk of cesarean delivery for fetal distress. Decelerations lasting 1 minute or longer have been reported to have an even worse prognosis (Bourgeois, 1984; Druzin, 1981; Pazos, 1982).
Hoskins and associates (1991) attempted to reine interpretation of testing that shows variable decelerations by adding sonographic estimation of amnionic luid volume. The incidence of cesarean delivery for intrapartum fetal distress progressively rose concurrently with the severity of variable decelerations and decline of amnionic luid volume. Severe variable decelerations during a nonstress test plus an amnionic luid index (AFI) ;5 em resulted in a 75-percent cesarean delivery rate. Fetal distress in labor, however, also frequently developed in those pregnancies with variable decelerations but with normal amounts of amnionic luid. Similar results were reported by Grubb and Paul (1992).
Smith and associates (1987) performed a detailed analysis of the causes of fetal death within 7 days of normal nons tress tests. The most common indication for testing was postterm pregnancy. he mean interval between testing and death was 4 days, with a range of 1 to 7 days. he single most common autopsy inding was meconium aspiration, oten associated with some type of umbilical cord abnormality. They concluded that an acute asphyxial insult had provoked fetal gasping. hey also concluded that nonstress testing was inadequate to preclude such an acute asphyxial event and that other biophysical characteristics might be beneicial. Importantly, assessment of amnionic luid volume was considered valuable. Other ascribed frequent causes of fetal death included intrauterine infection, abnormal cord position, malformations, and placental abruption.
Loud external sounds have been used to startle the fetus and thereby provoke heart rate acceleration-an acoustic stimulation nonstress test. A commercially available acoustic stimulator is positioned on the maternal abdomen, and a stimulus of 1 to 2 seconds is applied (Eller, 1995). his may be repeated up to three times for up to 3 seconds (American College of Obstetricians and Gynecologists, 2016). A positive response is deined as the rapid appearance of a qualiYing acceleration following stimulation (Devoe, 2008). In a randomized trial of 113 women undergoing nonstress testing, vibroacoustic stimulation shortened the average time of testing from 24 to 15 minutes (Perez-Delboy, 2002). Similar results were reported by Turitz and coworkers (2012). Laventhal and colleagues (2003) reported that fetal tachyarrhythmia could be provoked with vibroacoustic stimulation.