Procedures in Family Practice The Fetal Non-Stress Test C. Richard Kirkwood, MD, and Sam Eggertsen, MD Seattle, Washington The non-stress test has become a widely accepted method of screening for fetal distress in high-risk pregnancies. The pro­ cedure is technically simple, noninvasive, and when reactive (negative), a highly reliable predictor of fetal well-being for up to one week. This paper outlines the indications, performance, interpretation, and limits of the non-stress test as a standard evaluative tool for use by family physicians. The use of the oxytocin challenge test as a Schifrin et al5 and Trierweiler et al6 were first to means of predicting fetal well-being in high-risk observe that during the baseline period (prior to obstetric conditions has been well established for the onset of uterine contractions), accelerations two decades. Serious problems with this proce­ of fetal heart rate accompanying fetal movement dure, including the potential for inducing labor, were associated with uniformly good outcomes in relative technical complexity, expense, and a sig­ the oxytocin challenge test. Subsequently, other nificant false-positive rate (24 to 48 percent),1 have studies7,8 have confirmed that fetal heart rate given impetus to the acceptance of the non-stress accelerations with fetal movement are associated test.2’3 This procedure employs continuous elec­ with good fetal tolerance of labor. However, since tronic fetal monitoring, but unlike the oxytocin the test measures only one parameter of fetal challenge test, does not employ deliberate stimu­ health, the neurocardiac axis as it is affected lation of uterine contractions with Pitocin. by chronic hypoxia, other untoward events may The non-stress test offers significant advantages occur to adversely affect the fetus that will not be over the oxytocin challenge test as a screening predicted by this test.9 tool, including time savings and applicability to the outpatient setting. When reactive (negative), it provides reliable reassurance of fetal well-being for up to one week.4 Interpretation of the test can be easily mastered by physicians. Indications All pregnancies at high risk for uteroplacental insufficiency are candidates for non-stress testing. Postdatism and uncertain dates are the most com­ From the Department of Family Medicine, School of Medi­ cine, University of Washington, Seattle, Washington. Re­ mon indications. For postdatism, testing normally quests for reprints should be addressed to Dr. C. Richard begins at the 42nd week. Other indications are Kirkwood, Department of Family Medicine, RF-30, School of Medicine, University of Washington, Seattle, WA 98195. class A diabetics at term, pre-eclampsia, chronic ® 1983 Appleton-Century-Crofts THE JOURNAL OF FAMILY PRACTICE, VOL. 17, NO. 2: 311-319, 1983 311 FETAL NON-STRESS TEST hypertension, suspected intrauterine growth re­ sure adequate technical quality of the recordings, tardation, poor maternal weight gain, and de­ to record blood pressure, and to note times on the creased fetal movement. There are virtually no recording. contraindications to the non-stress test. The test involves a period of continuous exter­ A reactive test is in general an indication of fetal nal ultrasonic fetal monitoring. In small hospitals well-being, and if the pregnancy continues, the only a single monitor, often used for a variety of non-stress test can be repeated in one week, al­ monitoring functions in addition to the non-stress though twice weekly may be preferable.10 A non- testing, may be available. Cooperative lending reactive test should be repeated, preferably the agreements between institutions may solve bottle­ same day, and if reactive on repeat, the results necks and prevent undue delay in instituting provide reassurance of fetal well-being equal to an the procedure. A monitor capable of ultrasonic originally reactive test. If the results remain non- beat-to-beat fetal heart rate analysis (eg, Hewlett- reactive, an immediate oxytocin challenge test Packard #8040A) is desirable. should be scheduled and management decisions The monitoring room should be pleasant and made. relaxed and provide a reasonably quiet environ­ ment. The patient assumes a position compatible with placement of the external ultrasonic trans­ ducer on the abdomen (Figure 1). The semi- Fowler position is most convenient for the assist­ Procedure ant, but the left lateral Sims’ position is usually Outpatients are usually tested in specially adequate and more comfortable. The transducer is equipped monitoring rooms adjacent to the deliv­ attached to the monitor, and the recording equip­ ery area. Tests are scheduled in advance, and a ment is calibrated and checked for proper func­ minimum of one hour is allotted per procedure. tioning. The transducer is then moved on the Trained nursing personnel must be present to en- abdomen until a loud, consistent fetal heart rate 312 THE JOURNAL OF FAMILY PRACTICE, VOL. 17, NO. 2, 1983 FETAL NON-STRESS TEST Figure 2. Protocol for performing non-stress test is obtained. The mother is instructed in the use recommend stopping the test at this point, Brown of the external “ tocodynamometer” device to and Patrick11 have shown no increased morbidity permanently mark the fetal heart rate tracing or mortality in a large series (1,101 cases) for whenever she feels fetal movement. Some coach­ which a reactive pattern was obtained only after ing is usually necessary the first time a patient is 120 minutes of monitoring. A protocol for subse­ tested, since many women late in pregnancy may quent sequencing of tests is shown in Figure 2. ignore many fetal movements. Once a technically Maternal obesity, methyldopa, phenobarbital, satisfactory fetal heart rate baseline is established insulin, and recent amniocentesis have not been and the patient can demonstrate she can use the shown to affect non-stress test results.12 Phelan13 fetal movement indicator, the non-stress test is has demonstrated that fetal heart rate reactivity is started and conducted for 20 minutes. A physician diminished with chronic maternal smoking, al­ or technician is in attendance constantly to over­ though he failed to demonstrate whether this di­ see the testing, ensuring that the fetal heart rate minished reactivity was a direct function of the tracing is satisfactory and all fetal movements are smoking or related to the higher rate of intra­ noted. Fetal movement may decrease the intensity uterine growth retardation noted in the study of the ultrasonic signal, requiring repositioning or po) ulation. supporting the transducer by hand to maintain a continuous signal. If adequate fetal movements are noted in the first 20 minutes (defined as at least two fetal movements), the recording is terminated and inter­ Interpretation preted. If inadequate fetal movement has oc­ Several technical factors can invalidate a re­ curred, it can often be elicited by various maneu­ cording. Fetal heart rate monitoring should be vers, including giving fruit juice to raise blood continuous. Skipping is usually due to movement sugar levels, maternal activity, fundal pressure, or of the fetus and corrected by changing placement loud noise. It should be realized that the fetus of the transducer. In addition, the mother must be normally has sleep-wake cycles of up to 40 min­ attentive to fetal movement and capable of accu­ utes, and time may be the best way to elicit fetal rately noting it on the monitoring strip. movement. After such maneuvers, a second 20 An analysis of long-term (periodic) variability minutes of continuous monitoring is performed has classically been used to assess the non-stress using the same protocol. Although most authors test. Inclusion of beat-to-beat variability in the 313 the JOURNAL OF FAMILY PRACTICE, VOL. 17, NO. 2, 1983 FETAL NON-STRESS TEST — ISO----- _____ _ _ io n ___ ' ! A i 1 1 j U / ^ , 1 5 ° - /V> \ t -Vr, r \ V v 4 y K V'W r / '~ * - > V ra i V f v v v r - ' r ■ -- 1 j_o— 90--- 1 1 6 0 . ----- ”301------- Figure 3. Interpretation of reactive and nonreactive non-stress tests. (Top) Acceleration of fetal heart rate shown by arrows. (Bottom) Lack of reactivity and decelerations. FM shows fetal movement analysis of the test has also been suggested13"16 but tions, time period of test, amplitude of the accel­ is not yet widely accepted. eration, and duration of accelerations.4 A reactive A variety of criteria have been used to interpret test is generally accepted to be one with two to periodic variability, including number of accelera­ Continued on page 319 314 THE JOURNAL OF FAMILY PRACTICE, VOL. 17, NO. 2, 1983 FETAL NON-STRESS TEST Continued from page 314 pregnancies those fetuses that have a good proba­ three accelerations (of at least 15 beats per minute bility of favorable outcome with vaginal delivery. over 15 seconds) associated with fetal movement It has great utility, being less expensive and safer within a 40-minute observation period. Lack of than the oxytocin challenge test. The use and in­ accelerations with fetal movement or deceleration terpretation of this test can be easily mastered by constitutes a nonreactive (positive) test in which physicians. case an oxytocin challenge test is indicated. In­ termediate results, including some acceleration not meeting cutoff criteria, lack of fetal move­ ment, or poor beat-to-beat variability, are indica­ tors for repeat testing within 24 hours. Figure 3 shows examples of reactive and nonreactive non­ stress tests. In high-risk pregnancies with a reactive non­ References stress test, fetal morbidity should be anticipated in 1. Peck T: Physicians' subjectivity in evaluating oxy­ tocin challenge tests. Obstet Gynecol 56:13, 1980 the range of 2 to 3 percent.7 Nonreacting patterns 2. Richard F, Schifrin BS, Goupil I, et al: Non-stressed are predictive of morbidity in the range of 40 to 60 fetal heart rate monitoring in the antepartum period.