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FETAL SURVEILLANCE-UPDATE MAURICE L. DRUZIN, M.D. Department of Obstetrics and Gynecology The New York Hospital-Cornell Medical Center New York, New York
THE 20 YEARS BETWEEN 1968 and 1988 have been marked
by rapid advances in obstetrical technology. These advances have allowed noninvasive fetal evaluation, and an important advance in fetal evaluation has been real time ultrasonography. Antepartum fetal heart rate testing, which uses elements of continuous fetal heart rate monitoring to determine fetal condition, has been the standard method of evaluation. In the antepartum period, the commonly used fetal evaluation techniques of continuous fetal heart rate monitoring have been the contraction stress test' and the nonstress test.2-4 The contraction stress test, previously called the oxytocin challenge test, imposes a physiologic stress upon the fetus by means of uterine contractions, which are known to decrease intervillous blood flow.5,6 These tests were developed to indicate uteroplacental insufficiency, and therefore to predict a fetus that would not be able to tolerate contractions in labor. This test has proved highly reliable in the prediction of the fetus at risk but has the disadvantage of having a substantial false abnormal rate. The nonstress test evaluates the fetal heart rate response to fetal movement. By combining maternal perception of fetal movement with objective evaluation of fetal heart rate response to this movement, an assessment of fetal condition can be made that integrates many complex physiological indices. Fetal heart rate response to fetal movement requires an intact peripheral nervous system, central nervous system, autonomic nervous system, and responsive cardiovascular system.3,4 INDICATIONS FOR ANTEPARTUM FETAL HEART RATE TESTING
Indications for antepartum fetal heart rate testing include any condition, maternal or fetal, that may subject the fetus to increased perinatal mortality or morbidity. Maternal conditions include diabetes mellitus, hypertension, anemia, hemaglobinopathies, heart disease, pulmonary disease, collagen vascular disease, and any other medical or surgical condition that may impact on Address for reprint requests: 525 East 68th Street, Room M-036, New York, N.Y. 10021
Bull. N.Y. Acad. Med.
247 FETAL FETAL SURVEILLANCE SURVEILLANCE247
the fetus. Obstetrical indications for antepartum fetal heart rate testing include suspected intrauterine growth retardation, previous stillbirth, perception of decreased fetal movement, premature labor and premature rupture of the membranes, multiple gestation, and any other condition associated with increased perinatal loss. GESTATIONAL AGE AT WHICH ANTEPARTUM TESTING SHOULD BE INSTITUTED As a general rule, antepartum fetal heart rate testing should be instituted when decisions about intervention can be made on detection of abnormal testing. Conventional wisdom would have antepartum testing begin at a point in gestation when intervention in the form of delivery would allow reasonable neonatal survival.7,8 However, early antepartum testing may be of benefit in detecting a fetus at increased risk and allowing for intervention other than delivery to be instituted.9
CONTRAINDICATIONS TO ANTEPARTUM TESTING
There are no contraindications to nonstress testing. Relatively simple to perform, it has the advantage over contraction stress testing of more rapid testing sequence, no contraindications, and no intravenous oxytocin infusion. Contraction stress testing is contraindicated in the presence of premature labor, premature multiple gestation, incompetent cervix, previous vertical uterine incision, placenta previa, premature rupture of amniotic membranes, polyhydramnios, and third trimester bleeding. CLINICAL ASPECTS OF NONSTRESS TESTING
The nonstress test is performed using an external system to monitor fetal movement, uterine contractions, fetal heart rate. Uterine activity is obtained with a tocodynamometer strapped to the abdomen in conjunction with manual palpation of the uterus by the examiner. This method will register the frequency and relative duration but not the actual strength of the contractions. The patient is given an "event marker" with which she can register perceived fetal movements on the strip chart. Thus, patient and examiner both record fetal movements. The fetal heart rate can be derived from ultrasonic, phonocardiogram, or abdominal wall electrocardiogram signals. Ultrasound will provide an adequate fetal heart rate tracing in as many as 95% of the cases, while the success rate of the other two methods has been somewhat lower. A nonstress test is reactive in the presence of two fetal heart rate accelerations greater than 15 beats per minute, lasting at least 15 seconds during a 20 Vol. 66, No. 3, May-June 1990
248
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ML. DRUZIN M.L. DRUZIN
minute period. Accelerations in the absence of perceived fetal movement are counted, as it has been shown that approximately 20% of fetal movement is not perceived but can be demonstrated by real time ultrasound. The test is nonreactive when it fails to meet the above criteria in two consecutive 20 minute periods. Fetal bradycardia is defined as a decrease from the baseline heart rate of at least 40 beats per minute or as a baseline of 90 beats per minute or less, lasting at least 60 seconds. CLINICAL ASPECTS OF THE CONTRACTION STRESS TEST
Contraction stress testing is performed while the patient is in the semiFowler's position to avoid the supine-hypotensive syndrome. A baseline period of 10-15 minutes is used to assess fetal heart rate characteristics and the possibility of periodic changes. Blood pressure should be monitored every 10 minutes to identify supine hypotension that might provoke an abnormal contraction stress test. Uterine activity is evaluated for spontaneous contractions. If recurrent late decelerations occur with spontaneous contractions, the test is positive whatever the frequency of uterine contractions. In patients having fewer than three spontaneous contractions in 10 minutes in which no decelerations are noted, stimulation of the nipple by the patient is used to obviate the need for intravenous oxytocin. This procedure has resulted in a qualifying contraction stress test in over 70% of cases. The test is considered qualifying in the presence of three contractions in 10 minutes, felt by the patient or the observer, lasting 40 seconds and equal in intensity. The negative (or normal) contraction stress test is defined as one in which no late decelerations occur during a 10-minute period in which three contractions are recorded. A test is considered positive (or abnormal) when late decelerations occur following each contraction during a 10-minute period. The term equivocal is reserved for the test in which neither a positive nor a negative 10-minute window is obtained. CLINICAL INTERPRETATION OF ANTEPARTUM TESTING
There is some controversy as to whether a contraction stress or a nonstress test should be the primary modality for testing. This controversy has persisted and the literature supports both sides of the coin. 10,1 1 One incontestible point is that, regardless of type of testing, patients who undergo some type of testing have an improved outcome over patients who do not in situations Bull. N.Y. Acad. Med.
FETAL SURVEILLANCE FETALSURVELLANC
249 24
where antepartum evaluation is indicated. 10,12,13 One of the misunderstood aspects of antepartum fetal heart rate testing is the idea that in nonstress testing reactivity of the fetal heart rate is the only criterion that predicts fetal condition. Other characteristics of the nonstress test are equally important, particularly evidence of uterine activity and periodic and nonperiodic changes of the fetal heart rate in the form of decelerations. 14-16 Similarly, with the contraction stress test, other aspects of heart rate such as reactivity have not been considered in interpretation. The combination of a nonreactive nonstress test/negative contraction stress test has been shown to have a higher fetal death rate compared to the reactive nonstress test alone. 17 This combination is now considered "equivocal" and not "normal," and requires retesting within 24 hours (Figure 1). The combination of the tests therefore should look at all aspects of fetal heart rate, including: baseline heart rate; reactivity; periodic decelerations, including late decelerations and variable decelerations; and nonperiodic decelerations, specifically bradycardia. FETAL BRADYCARDIA AND VARIABLE DECELERATIONS
Fetal bradycardia during antepartum testing predicts a fetus at risk for fetal distress during labor and also the risk of intrauterine growth retardation. A very high incidence of fetal distress during labor in patients who were delivered following detection of fetal bradycardia during antepartum testing was noted in one study, 16 an observation supported by a subsequent study by the same authors18 in which a high incidence of fetal distress during labor was again noted. In two other related articles,13,14 the authors demonstrated a 25% fetal death rate in patients who showed fetal bradycardia during antepartum fetal heart rate testing and who subsequently were not delivered but were managed without delivery and with repeat testing (Table I). That perinatal mortality in both these studies was confined to the antepartum period illustrates the importance of bradycardia as an indicator of risk for fetal demise. The incidence of small for gestational age fetuses with evidence of intrauterine growth retardation was high in all these studies. In our study of 121 patients18 the outcome of fetal bradycardia did not differ among three different gestational age groups (Table II). Twenty six cases of nonreactive nonstress tests with positive contraction stress tests were observed during the same period as the bradycardia series. The nonreactive nonstress test with positive contraction stress test has been reported to be associated with the highest perinatal mortality. 10, 19 The inciVol. 66, No. 3, May-June 1990
250
M. L. DRUZIN
Fig. 1. Antepartum fetal heart heart monitoring protocol at The New York Hospital
dence of intrapartum complications as well as fetal outcome were similar in both groups, emphasizing the predictive reliability of bradycardia for perinatal outcome. Variable decelerations during antepartum fetal heart rate testing, particularly in the post dates population, have also been shown to predict subsequent complications in both in labor and in the neonatal period.20,21 FACTORS THAT MAY INFLUENCE ANTEPARTUM FETAL HEART RATE TESTING
Numerous external stimuli have been used in an attempt to decrease the time required for a test and to decrease the incidence of false abnormal Bull. N.Y. Acad. Med.
SURVEILLANCE FETAL SURVEILLANCE
FETAL
251 251
TABLE I. MANAGEMENT OF ANTEPARTUM FETAL BRADYCARDIA Druzin Druzin Dashow Bourgeois 1989 1981 1984 1984 (Ref. 14) (Ref. 18) (Ref. 16) (Ref. 15) Bradycardia 121/3046 12/800 8/476 24/1725 (1.5%) (4%) (2%) (1%) delivery expectant expectant delivery Management 74 (61%) 2 (25%) 5 (42%) 18 (75%) Cesarean section 76 (75%) 4 (100%) 8 (89%) 14 (58%) Fetal distress in labor 8 (7%) 3 (38%) 7 (58%) 3 (13%) Fetus small for gestational age 0 2 (25%) 3 (25%) 0 Antepartum Fetal death 25/1,000* 250/1,000 250/1,000 0 Perinatal mortality *8/1,000 when corrected for congenital anomalies
TABLE II. BRADYCARDIA OUTCOME BY GESTATIONAL AGE >42 weeks 40-42 weeks 36-40 weeks N=21 N=59 N=41 39/51 (76%) 15/19 (79%) 23/31 (74%) Abnormal fetal heart rate in labor 19 (32%) 10 (43%) 12 (29%) Cesarean section for fetal distress 0 3 (7%) 2 (3%) 5 minute APGAR
FETAL SURVEILLANCE-UPDATE MAURICE L. DRUZIN, M.D. Department of Obstetrics and Gynecology The New York Hospital-Cornell Medical Center New York, New York
THE 20 YEARS BETWEEN 1968 and 1988 have been marked
by rapid advances in obstetrical technology. These advances have allowed noninvasive fetal evaluation, and an important advance in fetal evaluation has been real time ultrasonography. Antepartum fetal heart rate testing, which uses elements of continuous fetal heart rate monitoring to determine fetal condition, has been the standard method of evaluation. In the antepartum period, the commonly used fetal evaluation techniques of continuous fetal heart rate monitoring have been the contraction stress test' and the nonstress test.2-4 The contraction stress test, previously called the oxytocin challenge test, imposes a physiologic stress upon the fetus by means of uterine contractions, which are known to decrease intervillous blood flow.5,6 These tests were developed to indicate uteroplacental insufficiency, and therefore to predict a fetus that would not be able to tolerate contractions in labor. This test has proved highly reliable in the prediction of the fetus at risk but has the disadvantage of having a substantial false abnormal rate. The nonstress test evaluates the fetal heart rate response to fetal movement. By combining maternal perception of fetal movement with objective evaluation of fetal heart rate response to this movement, an assessment of fetal condition can be made that integrates many complex physiological indices. Fetal heart rate response to fetal movement requires an intact peripheral nervous system, central nervous system, autonomic nervous system, and responsive cardiovascular system.3,4 INDICATIONS FOR ANTEPARTUM FETAL HEART RATE TESTING
Indications for antepartum fetal heart rate testing include any condition, maternal or fetal, that may subject the fetus to increased perinatal mortality or morbidity. Maternal conditions include diabetes mellitus, hypertension, anemia, hemaglobinopathies, heart disease, pulmonary disease, collagen vascular disease, and any other medical or surgical condition that may impact on Address for reprint requests: 525 East 68th Street, Room M-036, New York, N.Y. 10021
Bull. N.Y. Acad. Med.
247 FETAL FETAL SURVEILLANCE SURVEILLANCE247
the fetus. Obstetrical indications for antepartum fetal heart rate testing include suspected intrauterine growth retardation, previous stillbirth, perception of decreased fetal movement, premature labor and premature rupture of the membranes, multiple gestation, and any other condition associated with increased perinatal loss. GESTATIONAL AGE AT WHICH ANTEPARTUM TESTING SHOULD BE INSTITUTED As a general rule, antepartum fetal heart rate testing should be instituted when decisions about intervention can be made on detection of abnormal testing. Conventional wisdom would have antepartum testing begin at a point in gestation when intervention in the form of delivery would allow reasonable neonatal survival.7,8 However, early antepartum testing may be of benefit in detecting a fetus at increased risk and allowing for intervention other than delivery to be instituted.9
CONTRAINDICATIONS TO ANTEPARTUM TESTING
There are no contraindications to nonstress testing. Relatively simple to perform, it has the advantage over contraction stress testing of more rapid testing sequence, no contraindications, and no intravenous oxytocin infusion. Contraction stress testing is contraindicated in the presence of premature labor, premature multiple gestation, incompetent cervix, previous vertical uterine incision, placenta previa, premature rupture of amniotic membranes, polyhydramnios, and third trimester bleeding. CLINICAL ASPECTS OF NONSTRESS TESTING
The nonstress test is performed using an external system to monitor fetal movement, uterine contractions, fetal heart rate. Uterine activity is obtained with a tocodynamometer strapped to the abdomen in conjunction with manual palpation of the uterus by the examiner. This method will register the frequency and relative duration but not the actual strength of the contractions. The patient is given an "event marker" with which she can register perceived fetal movements on the strip chart. Thus, patient and examiner both record fetal movements. The fetal heart rate can be derived from ultrasonic, phonocardiogram, or abdominal wall electrocardiogram signals. Ultrasound will provide an adequate fetal heart rate tracing in as many as 95% of the cases, while the success rate of the other two methods has been somewhat lower. A nonstress test is reactive in the presence of two fetal heart rate accelerations greater than 15 beats per minute, lasting at least 15 seconds during a 20 Vol. 66, No. 3, May-June 1990
248
248
ML. DRUZIN M.L. DRUZIN
minute period. Accelerations in the absence of perceived fetal movement are counted, as it has been shown that approximately 20% of fetal movement is not perceived but can be demonstrated by real time ultrasound. The test is nonreactive when it fails to meet the above criteria in two consecutive 20 minute periods. Fetal bradycardia is defined as a decrease from the baseline heart rate of at least 40 beats per minute or as a baseline of 90 beats per minute or less, lasting at least 60 seconds. CLINICAL ASPECTS OF THE CONTRACTION STRESS TEST
Contraction stress testing is performed while the patient is in the semiFowler's position to avoid the supine-hypotensive syndrome. A baseline period of 10-15 minutes is used to assess fetal heart rate characteristics and the possibility of periodic changes. Blood pressure should be monitored every 10 minutes to identify supine hypotension that might provoke an abnormal contraction stress test. Uterine activity is evaluated for spontaneous contractions. If recurrent late decelerations occur with spontaneous contractions, the test is positive whatever the frequency of uterine contractions. In patients having fewer than three spontaneous contractions in 10 minutes in which no decelerations are noted, stimulation of the nipple by the patient is used to obviate the need for intravenous oxytocin. This procedure has resulted in a qualifying contraction stress test in over 70% of cases. The test is considered qualifying in the presence of three contractions in 10 minutes, felt by the patient or the observer, lasting 40 seconds and equal in intensity. The negative (or normal) contraction stress test is defined as one in which no late decelerations occur during a 10-minute period in which three contractions are recorded. A test is considered positive (or abnormal) when late decelerations occur following each contraction during a 10-minute period. The term equivocal is reserved for the test in which neither a positive nor a negative 10-minute window is obtained. CLINICAL INTERPRETATION OF ANTEPARTUM TESTING
There is some controversy as to whether a contraction stress or a nonstress test should be the primary modality for testing. This controversy has persisted and the literature supports both sides of the coin. 10,1 1 One incontestible point is that, regardless of type of testing, patients who undergo some type of testing have an improved outcome over patients who do not in situations Bull. N.Y. Acad. Med.
FETAL SURVEILLANCE FETALSURVELLANC
249 24
where antepartum evaluation is indicated. 10,12,13 One of the misunderstood aspects of antepartum fetal heart rate testing is the idea that in nonstress testing reactivity of the fetal heart rate is the only criterion that predicts fetal condition. Other characteristics of the nonstress test are equally important, particularly evidence of uterine activity and periodic and nonperiodic changes of the fetal heart rate in the form of decelerations. 14-16 Similarly, with the contraction stress test, other aspects of heart rate such as reactivity have not been considered in interpretation. The combination of a nonreactive nonstress test/negative contraction stress test has been shown to have a higher fetal death rate compared to the reactive nonstress test alone. 17 This combination is now considered "equivocal" and not "normal," and requires retesting within 24 hours (Figure 1). The combination of the tests therefore should look at all aspects of fetal heart rate, including: baseline heart rate; reactivity; periodic decelerations, including late decelerations and variable decelerations; and nonperiodic decelerations, specifically bradycardia. FETAL BRADYCARDIA AND VARIABLE DECELERATIONS
Fetal bradycardia during antepartum testing predicts a fetus at risk for fetal distress during labor and also the risk of intrauterine growth retardation. A very high incidence of fetal distress during labor in patients who were delivered following detection of fetal bradycardia during antepartum testing was noted in one study, 16 an observation supported by a subsequent study by the same authors18 in which a high incidence of fetal distress during labor was again noted. In two other related articles,13,14 the authors demonstrated a 25% fetal death rate in patients who showed fetal bradycardia during antepartum fetal heart rate testing and who subsequently were not delivered but were managed without delivery and with repeat testing (Table I). That perinatal mortality in both these studies was confined to the antepartum period illustrates the importance of bradycardia as an indicator of risk for fetal demise. The incidence of small for gestational age fetuses with evidence of intrauterine growth retardation was high in all these studies. In our study of 121 patients18 the outcome of fetal bradycardia did not differ among three different gestational age groups (Table II). Twenty six cases of nonreactive nonstress tests with positive contraction stress tests were observed during the same period as the bradycardia series. The nonreactive nonstress test with positive contraction stress test has been reported to be associated with the highest perinatal mortality. 10, 19 The inciVol. 66, No. 3, May-June 1990
250
M. L. DRUZIN
Fig. 1. Antepartum fetal heart heart monitoring protocol at The New York Hospital
dence of intrapartum complications as well as fetal outcome were similar in both groups, emphasizing the predictive reliability of bradycardia for perinatal outcome. Variable decelerations during antepartum fetal heart rate testing, particularly in the post dates population, have also been shown to predict subsequent complications in both in labor and in the neonatal period.20,21 FACTORS THAT MAY INFLUENCE ANTEPARTUM FETAL HEART RATE TESTING
Numerous external stimuli have been used in an attempt to decrease the time required for a test and to decrease the incidence of false abnormal Bull. N.Y. Acad. Med.
SURVEILLANCE FETAL SURVEILLANCE
FETAL
251 251
TABLE I. MANAGEMENT OF ANTEPARTUM FETAL BRADYCARDIA Druzin Druzin Dashow Bourgeois 1989 1981 1984 1984 (Ref. 14) (Ref. 18) (Ref. 16) (Ref. 15) Bradycardia 121/3046 12/800 8/476 24/1725 (1.5%) (4%) (2%) (1%) delivery expectant expectant delivery Management 74 (61%) 2 (25%) 5 (42%) 18 (75%) Cesarean section 76 (75%) 4 (100%) 8 (89%) 14 (58%) Fetal distress in labor 8 (7%) 3 (38%) 7 (58%) 3 (13%) Fetus small for gestational age 0 2 (25%) 3 (25%) 0 Antepartum Fetal death 25/1,000* 250/1,000 250/1,000 0 Perinatal mortality *8/1,000 when corrected for congenital anomalies
TABLE II. BRADYCARDIA OUTCOME BY GESTATIONAL AGE >42 weeks 40-42 weeks 36-40 weeks N=21 N=59 N=41 39/51 (76%) 15/19 (79%) 23/31 (74%) Abnormal fetal heart rate in labor 19 (32%) 10 (43%) 12 (29%) Cesarean section for fetal distress 0 3 (7%) 2 (3%) 5 minute APGAR
