that one acceleration was just as reliable as two in predicting healthy fetal status. Although a normal number and amplitude of accelerations seems to reflect fetal well-being, their absence does 60 not invariably predict fetal compromise. Indeed, some investigators have reported 90-percent or higher false-positive rates (Devoe, 1986). Because healthy fetuses may not move for periods of up to 75 minutes, some have considered that a longer duration of nonstress testing might increase the positive-predictive value of an abnormal, that is, nonreactive, test (Brown, 1981). In this scheme, either the test became reactive during a period up to 80 minutes or the test remained nonreactive for 120 minutes, which indicated that the fetus was very ill.
Not only do deinitions of normal nonstress test results difer, but the reproducibility ofinterpretations is problematic (Hage, 1985). Thus, although nons tress testing is popular, the reliability of test interpretation needs improvement.
Based on the foregoing, an abnormal nons tress test is not always ominous and can be seen with a sleeping fetus. Also, an abnormal test can revert to normal as the fetal condition changes, such as the example shown in
Figure 17-7. Importantly, a normal nonstress test can become abnormal if the fetal condition deteriorates.
There are abnormal patterns that reliably forecast severe fetal jeopardy (Fig. 17-8). Devoe and coworkers (1985) concluded that nonstress tests that were nonreactive for 90 minutes were almost invariably-93 percent-associated with significant perinatal pathology. Hammacher and coworkers (1968) described tracings with what they termed a silent oscillatoy pattern that he considered dangerous. his pattern consisted of a fetal heart rate baseline that oscillated less than 5 bpm and presumably indicated absent acceleration and beat-to-beat variability.
Visser and associates (1980) described a terminal cardiotocoram, which included: (1) baseline oscillation ofless than 5 bpm, (2) absent accelerations, and (3) late decelerations with spontaneous uterine contractions. hese results were similar to experiences from Parkland Hospital in which absence of accelerations during an 80-minute recording period in 27 fetuses was associated consistently with evidence of uteroplacental pathology (Leveno, 1983). he latter included fetal-growth restriction in 75ipercent, oligohydramnios in 80 percent, fetal acidemia in 40 percent, meconium in 30 percent, and placental infarction in 93 percent.
FIGURE 17-7 Two antepartum fetal heart rate (FHR) tracings in a 28-week pregnant woman with diabetic ketoacidosis. A. FHR tracing (upper panel) and accompanying contraction tracing (second panen. Tracing, obtained during maternal and fetal acidemia, shows absence of accelerations, diminished variability, and late decelerations with weak spontaneous contractions. B. Fetal heart rate tracing shows return of normal accelerations and variability of the fetal heart rate following correction of maternal acidemia.
Set originally rather arbitrarily at 7 days, the interval between tests appears to have been shortened as experience evolved with nonstress testing. According to the American College of Obstetricians and Gynecologists (2016), more frequent testing is advocated by some investigators for women with postterm pregnancy, multifetal gestation, pregestational diabetes, fetalgrowth restriction, or pregnancy hypertension. In these circumstances, some investigators perform twice-weekly tests, with additional testing completed for maternal or fetal deterioration regardless of the time elapsed since the last test. Others perform nonstress tests daily or even more frequently, such as with severe preeclampsia remote from term.