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Fetal acceleration test
Fetal acceleration test EDWARD H. BISHOP, M.D. Chapel Hill. North Carolina Five hundred thirty-one fetal acceleration tests were performed on 112 normal subjects at various gestational ages ranging between 22 and 41 weeks. Analysis of the results nweafed that the frequency of nonreactive tests was directly related to gestational age. ranging from 56% in the 22· to 25-week group to 6% in the 38· to 41-week group. During the $111\e !*foG 9t9 fetal accalerallon tests were performed on 339 high-risk subjects. When these were ·divided intO Q1'0UPS by gestational age, the frequency of nonreactive tests did not differ signifrcantly from that in the nonnal group of subjects. These data suggest three possible conclusions: (1) that the high frequency of false positive results does not justify the performance or utilization of such t..s before 30 weeks' gestational age; (2) that nonreactivity is probably a function of gutallonal age rather than an indication of fetal jeopardy; (3) that the frequency of "false positive" tests among the normal population may invalidate reliance on such tests for management of subjects in a high-risk category. (AM. J. 0BSTET. GYNECOL. 141:905, 1981.)
N'ONSTRESS ANTEPARTUM fetal monitoring has become a widely accepted method for evaluation of fetal condition. The obstetrics literature is replete with reports attesting to the validity and usefulness of this procedure. Many investigators have suggested that this should be a primary testing method or preliminary screening procedure either preceding or possibly replacing the need for the performance of contraction stress tests or oxytocin challenge tests. When performed on a "high-risk" population, the frequency of abnormal results (nonreactive nonstress tests) has been reported to be between 5% and 10%. It has been reported that clinical application of these test results has apparently contributed to a reduction of antepartum stillbirth rates. Unfortunately, there is a paucity of information regarding the significance of this procedure in a normal population. Although Schifrin and associates1 reported their experience with a "low-risk" population, their study appears biased by two factors.
First, 10% of the low-risk patients in their study became high risk, and second, the results were made known to the responsible physician whose subsequent actions were inHuenced by the test results. Trimbos and Keirse~ performed cardiotocography on a series of normal patients. They did not specifically rely on accelerations re lated to fetal activity but, by their criteria. reported that 37% showed suspicious patterns and concluded that "dearly normal pregnancies do not invariably provide normal antepar;:um CTG's." Neither Schifrin nor Trimbos and Keirse controlled their results by gestational age. This study was undertaken as an attempt: to determine the frequency of reactive and nonreactive nonstress patterns in a normal population at various stages of gestational age. Additionally, the freqt.Iency of abnormal tests in the '·normal" group was compared to the frequency of abnormal test results in a high-risk population studied in an identical. manner during the same period.
Material and methods From The Department of Obstetrics and Gynecology, School of Medicine of the University of North Carolina at Chapel Hill. Prrsented at the Second Combined Annw.zl Meeting of the American Gynt!cological Society and American Associati£m of Obstetricians and Gynecologists, Montreal, Quebec, Canada, May 20-23, 1981. Reprint requests: Edward H. Bishop, M.D., Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, 214 MacNider Building 202H, Chapel Hill, North Carolina27514. 0002-9378/81/240905+05$00.50/0 © !981 The C. V. Mosby Co.
One hundred twenty-two apparently normal patients were randomly selected from the clinic population by a request to serve as volunteer subjects. \Vhenever any significant complication occurred during the prenatal period, the subject was eliminated from th<~ study. Additionally, subjects were included onlv if they experienced a normal labor and delivery, if the neonatal Apgar scores were in the expected normal range, and if the infant was considered normal by pediatric exami905
906 Bishop
Det:emher 1:,, 19kl Am.J Ob,t<>t. Cnte
60
Table I. Indications for fetal acceleration tests in subjects with high-risk pregnancies
50
lndicatitm
40
%
Chronic hypertension Suspected prolonged pregnancy Preeclampsia Maternal diabetes Suspected intrauterine growth retardation Other pregnancy hypertension Miscellaneous Total
30 20 10
~\'n.
74
63
4i 42 35 20 __Q§_ 339
4243
Fig. 1. Percentage of nonreactive fetal acceleration tests among high-risk patients at various gestational periods.
60 50
40
% 30 20 10 22- 24- 26- 28- 30- 32- 34- 36- 38- 40- 42~
~
v
~
~
~
~
n
~
~
~
WEEKS Fig. 2. Percentage of nonreactive fetal acceleration tests among suspected high-risk subjects at various gestational periods.
nation while in the newborn nursery. Any exception to these conditions warranted elimination from the study group. By utilization of these standards, 10 subjects were excluded from the normal group. All test procedures were performed by one trained technician. In the majority of instances, the heart rate was recorded by phonocardiography although occasionally, when this was either unsatisfactory or unavailable, Doppler ultrasonography was used. After a preliminary observation period used to determine proper function of the equipment, the subjects were tested for a maximum of 30 minutes. However, if the test was obviously favorable in a shorter period of time, it was terminated earlier but never before completion of a 15-minute test period. Fetal activity was observed by either the mother or the technician and manually recorded on the record.ln the absence of adequate fetal activity, an attempt was made to "awaken'' or stimulate the fetus which, when successful, was followed by the standard test procedures. All test results were interpreted after discharge of the mother and the
infant from the hospital. The results were read blindly by a single observer without knowledge of gestational age, obstetric status, and normality or abnormality. The test r-esults were not made known to the attending physician and were not used for clinical management. Tracings were classified as reactive only when there were five or more episodes of fetal activity within the 30-minute test period combined with an acceleration of the fetal heart rate by at least I0 bpm synchronous with more than half of the episodes of fetal movement. Failure to attain either of these criter-ia (fewer than five episodes of fetal activity or acceleration with less than 50o/c of fetal movements) resulted in classification as nonreactive.
Results and comment Five hundred thirty-one tests ranging in number from one to 17 for each patient, were performed on 112 normal subjects. The frequency of nonreactive tests at varying gestational periods is illustrated in Fig. 1. It may be concluded from these data that fetal nonstress test results are invalid before attainment of 30 weeks' gestational age based on the observation that 42% of the tests in this period were nonreactive in spite of an eventual normal outcome. Parenthetically, these observations will seldom be clinically important because of the fact that indications for delivery before 30 weeks are unusual. From 30 and 41 weeks' gestational age, approximately 6% of the tests were classified as nonreactive. This observation indicates only that unfavorable test results can and do occur in normal pregnancies with a normal neonatal outcome. It strongly supports the suggestions made by others that reactive or favorable tests may be supportive of a good prognosis while unfavorable tests are only an indication for further evaluation by other investigative methods. These findings also suggest that fetal activity and the response of fetal heart rate to such activity may be a function of gestational age, fetal development, and fetal maturity rather than solely a function of fetal condition. During the same period 919 fetal acceleration tests were performed on 339 high-risk subjects. The tech-
Fetal acceleration test
Volume !41 "'umber R
nique and the protocol used \Vere exactly the same as for the normal subjects except that the results were made available to the attending physician requesting performance of the test. For the purposes of this study. however, the interpretation of results was made blindly as for the normal subjects, i.e., only after delivery and without knowledge of the indications, course of pregnancy, and outcome. The indications for performance of these tests are listed in Table I. The test results for the abnormal group controlled by gestational age are illustrated in Fig. 2. It is of interest that for each gestational age group (except for the postdate group) there was no significant difference in test results between the normal group and the abnormal group CFig. 3). The possibility must be conceded that in this abnormal group other circumstances (alone or combined with the test results) resulted in early termination of pregnancy and that these subjects did not have the opportunity for later examinations (with either normal or abnormal test results). It also must be considered that many of the alleged high-risk conditions were only suspected and that many of the subjects actuallv may have been normal. However, when analysis was confined only to those patients known to have documented obstetric complications jeopardizing fetal and neonatal survival (chronic hypertension, insulindependent maternal diabetes, moderate to severe preeclampsia, and pregnancy prolonged up to or beyond 42 weeks supported by a pediatric diagnosis of postmaturity). with the exception of the postdate group. the frequency of abnormal results did not differ significantly from that of eithet· the normal group or the entire ""high-risk" group (Fig. 4). The following conclusions were drawn: I. The frequencv of nonreactive fetal acceleration tests among apparentlv normal subjects is related to gestational age. 2. Interpretation of fetal acceleration tests should be related to gestational age. 3. The frequency of nonreactive test results prior to 30 weeks is sufficiently high that this test has little value or validity at early gestational ages. 4. There was no significant difference between the test resuits of normai and high-risk subjects for each gestational age between 30 and 42 weeks. 5. In a prolonged pregnancy, a nonreactive test appears to have serious implications and is probably of prediciivt' value.
--
6() ..-
NORMAL o---o HIGH RISK
~~~ .A\
40~
907
\
% 30
a.., 20
, ,/:)
10 22- 24- 2623 25 27
42· 43
Fig. 3. Comparison of percentage of nonreactive fetal accelcration tests among normal or suspected high-risk subjects.
-NORMAL SUSPECTED HIGH RISK o---o HIGH RISK
15
%10
5
3031
32~,3
34~5
3637
3839
4041
4243
WEEKS
Fig. 4. Percentage of abnormal fetal acceleration tests by gestational age related to obstetric status.
6. ReactiYe tests may be valuable as supportive evidence or as an encouraging exercise, but nonreacti\·e tests probably are of little clinical significance. 7. Unfavorable (nonreactive) test results should not be used alone for management of high-risk situations. It is apparent from these data that the results obtained from performance of fetal acceleration tests are related to gestational age and that interpretation of results must include consideration of this relationship. Except in the postdate group, there were no significant differences in results in the normal group and the high-risk group. This suggests that nonreactive tests should not be used alone, unsupported by other evaluation, for the managernent of high-risk situatiom. However. the results of this study in no wav negate the reported Yalue of reactive results.
REFERENCES
J ., et al.: Routine fetal heart rate monitoring in the antepartum period, Obstet. Gynecol. 54:21, 1979.
I. Schifrin, B. S., Faye, G., Amato,
2. Trimbos, J B., and Keirse, M. J N.C.: Significance of antepartum cardiotocography in normal pregnancy. Br . .J. Obstet. Gynaecol. 85:907, 1978.
908
Bishop ,\m.
Editors' note: This manuscript was revised after these
discussions were presented. Discussion DR.JOHNT. QUEENAN, Washington, D.C. In the last 3 years, more than 15 articles have appeared in the literature describing variations on the theme of the nonstress test. The criteria for a favorable or so-called "reactive test" depend upon demonstrating fetal heart rate acceleration generally in response to fetal mm:ement. The minimum criterion for accelerations in some studies is greater than 10 bpm, and in others it is greater than 15 bpm. Some authors require the accelerations to last more than 15 seconds: others do not specify any duration. Some authors permit stimulation of the fetus when the test is nonreactive, and others do not. Some investigators study the fetus for 10 minutes: others. up to 30 minutes. This wide variation of standards for a nonstress test provides so many permutations and combinations that it is almost impossible to compare one series with another. Dr. Bishop's presentation today has shown that fetal reactivity is a function of advancing gestational age. He has shown that this phenomenon pertains in both normal and high-risk pregnancies. Indeed, any attempt to evaluate fetal reactivity prior to 30 weeks' gestation would have very misleading results. In his study he has adapted criteria different from others in the literature. Dr. Bishop requires that fetal heart rate accelerations only be greater than I 0 bpm with no duration of acceleration specified. He requires that there be five accelerations in 30 minutes and additionally that 50% of them must be associated with fetal movement. This does not correspond to the criteria in studies that have prm·ed the efficacy of the nonstress test in decreasing the perinatal mortality rate in large series: therefore, it becomes \·ery difficult to compare his data with those of other studies. Dr. Bishop found that the number of nonreactive tests in the control group was the same as that in the high-risk pregnancy group. The incidence of nonreactive studies was approximately 69{, in both groups. Several authors have shown that the nonstress test is very efficacious in decreasing perinatal mortality in high-risk pregnancies. The findings of the nonstress test are a clinical correlation. Several thousand deliveries are necessary to prove its efficacy. The fact that the rate of nonreactive tests in the control population was similar to that in the high-risk population by no means invalidates the test. If more strict criteria for fetal heart rate accelerations were used, the number of false positive tests would be even higher. The nonstress test is used as a first line of defense in the high-risk pregnancy. The clinician does not act on the nonstress test alone but on other factors such as the clinical course, biochemical monitoring, the oxytocin challenge test, fetal movements, and fetal breathing.
Decernbt·r ! ~). 19K 1 J. Obstet. (;ynt-cnl
Fetal sleep cycles and glucose le\·els affect the nonstress test and must be taken into accol!nt whcu the nonstress test is performed. The high false pm.itive rate is a disadvantage that the clinician must cope with. cl he benefit of the test-the low false negative rate-far outweighs this disadvantage. I would like to ask Dr. Bishop: ( 1) Why did you select these criteria? (2) What was the clinical correlation in terms of morbidity and mortality of the nonreactive nonstress tests? (3) Do you believe your findings would be different if you used more strict criteria to define accelerations? DR. MoRTIMER RoSEN, Cleveland, Ohio. I would like to compliment Dr. Bishop on the work he has presented and comment specifically on two points, the study of the normal population and the study of fetuses in utero prior to 30 weeks. We used similar noniroring techniques and instruments, but the speed of the paper is increased tenfold and the abdominal strain gauge is used at its highest setting, which enables us to determine more dearly the characteristics of the recording. Several investigators, including Dr. Sovolcon, assisted by Dr. Dierker and myself, studied fetuses between 20 and 30 weeks of gestational age. What we found in that population was that after ~0 weeks, when the fetus moves and the movement is more than l second in duration, 90'/f of the time there will be a cardimascular response, and in this normal population that response will be a fetal heart rate acceleration. In marked contrast, prior to 30 weeks of gestation and with e\·en more movement before the twenty-eighth week, half of the time there will he no discernible heart rate change when the fetus moves. Second, and an e\·en more interesting fact, is that before 28 weeks acceleration is not the normal fetal response. Rather there is a fetal heart rate deceleration in almost half of the responses. This would emphasize the second point Dr. Bishop made. If this test is to be used in the less mature fetus, new criteria for a normal nonstress test will have to be obtained. DR. CALVIN HOBEL, Torrance, California. We are now recognizing a difference between the sex of the fetus and maturation and the risk of morbidity and mortality. We are, in a sense. dealing with two populations of patients in the uterus, male and female ones. Dr. Bishop, did you look at the difference between the male fetus and the female fetus in terms of the incidence of nonreactivity? DR. RICHARD PAUL, Los Angeles, California. I noticed that 10 patients were eliminated from the normal group, and I wondered if you might comment on the findings of antepartum monitoring in that particular group of subjects who were dropped and apparently developed some abnormality. DR. BISHOP (Closing). First, Dr. Paul, as far as what happened to the group who were eliminated, there
Volume HI :\umber H
were only I 0 of them and I do not remember how many tests they had, but the numbers were not really significant. They were eliminated for the indications 1 mentioned before. By just looking at them casually there wa~ no particularly different pattern in the number or the frequencv of reactivity or nonreactivity in that group. Whenever one presents a paper the discussants alwavs send one home to do more work. Now I have to go back and look at sex to see if there is any difference. I cannot comment on Dr. Rosen's work except to be fascinated bv his findings. We have had no experience in this area. I share Dr. Queenan's feeling that it is regrettable that we have had no standards to go by. I do not know how many types of nons tress tests there are; I think he mentioned a large number, which is, indeed, a problem. We used the same standard during the entire study. We are not using this standard at the present time since we are using a shorter period of time. When I reread all of these tracings and used the other standards, our results did not change significantly. Occasionally when we used 15 as a standard, one or two were changed as to categorv. In generaL if I had done the analysis with
Fetal acceleration test 909
these other standards, I believe the result' would have been about the same. However, the alternate interpretive methods would not have been performed blindly. I knew which were normal and abnormal: therefore, I thought we should stay with the original ~tandards. However, I do not reallv think it make, 'en much difference. \Ve. too, were concerned about glucos<, levels, and none of these tests was clone after a period of maternal fasting because that does make a differeun', A recent report indicates that the I 0-minute test may not be long enough. Even the :W-minute test we use may not be long enough. Possibly we should use an hour or an hour and a half because or the time imervals of sleep and activity of the fetus. :Mavbe we han~ erred in using the shorter test rather than the longer one. I do not han~ am: inf(Jrmation on morbidity and mortality. In the high-risk group it appears that a number of the morbidities were predicted, hut there are so many other factors that I cannot :~he a direcr answer to that question. I do not have a follow-up for anv of ;he infants other than at the time or discharge from rhe nurser\.
N'ONSTRESS ANTEPARTUM fetal monitoring has become a widely accepted method for evaluation of fetal condition. The obstetrics literature is replete with reports attesting to the validity and usefulness of this procedure. Many investigators have suggested that this should be a primary testing method or preliminary screening procedure either preceding or possibly replacing the need for the performance of contraction stress tests or oxytocin challenge tests. When performed on a "high-risk" population, the frequency of abnormal results (nonreactive nonstress tests) has been reported to be between 5% and 10%. It has been reported that clinical application of these test results has apparently contributed to a reduction of antepartum stillbirth rates. Unfortunately, there is a paucity of information regarding the significance of this procedure in a normal population. Although Schifrin and associates1 reported their experience with a "low-risk" population, their study appears biased by two factors.
First, 10% of the low-risk patients in their study became high risk, and second, the results were made known to the responsible physician whose subsequent actions were inHuenced by the test results. Trimbos and Keirse~ performed cardiotocography on a series of normal patients. They did not specifically rely on accelerations re lated to fetal activity but, by their criteria. reported that 37% showed suspicious patterns and concluded that "dearly normal pregnancies do not invariably provide normal antepar;:um CTG's." Neither Schifrin nor Trimbos and Keirse controlled their results by gestational age. This study was undertaken as an attempt: to determine the frequency of reactive and nonreactive nonstress patterns in a normal population at various stages of gestational age. Additionally, the freqt.Iency of abnormal tests in the '·normal" group was compared to the frequency of abnormal test results in a high-risk population studied in an identical. manner during the same period.
Material and methods From The Department of Obstetrics and Gynecology, School of Medicine of the University of North Carolina at Chapel Hill. Prrsented at the Second Combined Annw.zl Meeting of the American Gynt!cological Society and American Associati£m of Obstetricians and Gynecologists, Montreal, Quebec, Canada, May 20-23, 1981. Reprint requests: Edward H. Bishop, M.D., Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, 214 MacNider Building 202H, Chapel Hill, North Carolina27514. 0002-9378/81/240905+05$00.50/0 © !981 The C. V. Mosby Co.
One hundred twenty-two apparently normal patients were randomly selected from the clinic population by a request to serve as volunteer subjects. \Vhenever any significant complication occurred during the prenatal period, the subject was eliminated from th<~ study. Additionally, subjects were included onlv if they experienced a normal labor and delivery, if the neonatal Apgar scores were in the expected normal range, and if the infant was considered normal by pediatric exami905
906 Bishop
Det:emher 1:,, 19kl Am.J Ob,t<>t. Cnte
60
Table I. Indications for fetal acceleration tests in subjects with high-risk pregnancies
50
lndicatitm
40
%
Chronic hypertension Suspected prolonged pregnancy Preeclampsia Maternal diabetes Suspected intrauterine growth retardation Other pregnancy hypertension Miscellaneous Total
30 20 10
~\'n.
74
63
4i 42 35 20 __Q§_ 339
4243
Fig. 1. Percentage of nonreactive fetal acceleration tests among high-risk patients at various gestational periods.
60 50
40
% 30 20 10 22- 24- 26- 28- 30- 32- 34- 36- 38- 40- 42~
~
v
~
~
~
~
n
~
~
~
WEEKS Fig. 2. Percentage of nonreactive fetal acceleration tests among suspected high-risk subjects at various gestational periods.
nation while in the newborn nursery. Any exception to these conditions warranted elimination from the study group. By utilization of these standards, 10 subjects were excluded from the normal group. All test procedures were performed by one trained technician. In the majority of instances, the heart rate was recorded by phonocardiography although occasionally, when this was either unsatisfactory or unavailable, Doppler ultrasonography was used. After a preliminary observation period used to determine proper function of the equipment, the subjects were tested for a maximum of 30 minutes. However, if the test was obviously favorable in a shorter period of time, it was terminated earlier but never before completion of a 15-minute test period. Fetal activity was observed by either the mother or the technician and manually recorded on the record.ln the absence of adequate fetal activity, an attempt was made to "awaken'' or stimulate the fetus which, when successful, was followed by the standard test procedures. All test results were interpreted after discharge of the mother and the
infant from the hospital. The results were read blindly by a single observer without knowledge of gestational age, obstetric status, and normality or abnormality. The test r-esults were not made known to the attending physician and were not used for clinical management. Tracings were classified as reactive only when there were five or more episodes of fetal activity within the 30-minute test period combined with an acceleration of the fetal heart rate by at least I0 bpm synchronous with more than half of the episodes of fetal movement. Failure to attain either of these criter-ia (fewer than five episodes of fetal activity or acceleration with less than 50o/c of fetal movements) resulted in classification as nonreactive.
Results and comment Five hundred thirty-one tests ranging in number from one to 17 for each patient, were performed on 112 normal subjects. The frequency of nonreactive tests at varying gestational periods is illustrated in Fig. 1. It may be concluded from these data that fetal nonstress test results are invalid before attainment of 30 weeks' gestational age based on the observation that 42% of the tests in this period were nonreactive in spite of an eventual normal outcome. Parenthetically, these observations will seldom be clinically important because of the fact that indications for delivery before 30 weeks are unusual. From 30 and 41 weeks' gestational age, approximately 6% of the tests were classified as nonreactive. This observation indicates only that unfavorable test results can and do occur in normal pregnancies with a normal neonatal outcome. It strongly supports the suggestions made by others that reactive or favorable tests may be supportive of a good prognosis while unfavorable tests are only an indication for further evaluation by other investigative methods. These findings also suggest that fetal activity and the response of fetal heart rate to such activity may be a function of gestational age, fetal development, and fetal maturity rather than solely a function of fetal condition. During the same period 919 fetal acceleration tests were performed on 339 high-risk subjects. The tech-
Fetal acceleration test
Volume !41 "'umber R
nique and the protocol used \Vere exactly the same as for the normal subjects except that the results were made available to the attending physician requesting performance of the test. For the purposes of this study. however, the interpretation of results was made blindly as for the normal subjects, i.e., only after delivery and without knowledge of the indications, course of pregnancy, and outcome. The indications for performance of these tests are listed in Table I. The test results for the abnormal group controlled by gestational age are illustrated in Fig. 2. It is of interest that for each gestational age group (except for the postdate group) there was no significant difference in test results between the normal group and the abnormal group CFig. 3). The possibility must be conceded that in this abnormal group other circumstances (alone or combined with the test results) resulted in early termination of pregnancy and that these subjects did not have the opportunity for later examinations (with either normal or abnormal test results). It also must be considered that many of the alleged high-risk conditions were only suspected and that many of the subjects actuallv may have been normal. However, when analysis was confined only to those patients known to have documented obstetric complications jeopardizing fetal and neonatal survival (chronic hypertension, insulindependent maternal diabetes, moderate to severe preeclampsia, and pregnancy prolonged up to or beyond 42 weeks supported by a pediatric diagnosis of postmaturity). with the exception of the postdate group. the frequency of abnormal results did not differ significantly from that of eithet· the normal group or the entire ""high-risk" group (Fig. 4). The following conclusions were drawn: I. The frequencv of nonreactive fetal acceleration tests among apparentlv normal subjects is related to gestational age. 2. Interpretation of fetal acceleration tests should be related to gestational age. 3. The frequency of nonreactive test results prior to 30 weeks is sufficiently high that this test has little value or validity at early gestational ages. 4. There was no significant difference between the test resuits of normai and high-risk subjects for each gestational age between 30 and 42 weeks. 5. In a prolonged pregnancy, a nonreactive test appears to have serious implications and is probably of prediciivt' value.
--
6() ..-
NORMAL o---o HIGH RISK
~~~ .A\
40~
907
\
% 30
a.., 20
, ,/:)
10 22- 24- 2623 25 27
42· 43
Fig. 3. Comparison of percentage of nonreactive fetal accelcration tests among normal or suspected high-risk subjects.
-NORMAL SUSPECTED HIGH RISK o---o HIGH RISK
15
%10
5
3031
32~,3
34~5
3637
3839
4041
4243
WEEKS
Fig. 4. Percentage of abnormal fetal acceleration tests by gestational age related to obstetric status.
6. ReactiYe tests may be valuable as supportive evidence or as an encouraging exercise, but nonreacti\·e tests probably are of little clinical significance. 7. Unfavorable (nonreactive) test results should not be used alone for management of high-risk situations. It is apparent from these data that the results obtained from performance of fetal acceleration tests are related to gestational age and that interpretation of results must include consideration of this relationship. Except in the postdate group, there were no significant differences in results in the normal group and the high-risk group. This suggests that nonreactive tests should not be used alone, unsupported by other evaluation, for the managernent of high-risk situatiom. However. the results of this study in no wav negate the reported Yalue of reactive results.
REFERENCES
J ., et al.: Routine fetal heart rate monitoring in the antepartum period, Obstet. Gynecol. 54:21, 1979.
I. Schifrin, B. S., Faye, G., Amato,
2. Trimbos, J B., and Keirse, M. J N.C.: Significance of antepartum cardiotocography in normal pregnancy. Br . .J. Obstet. Gynaecol. 85:907, 1978.
908
Bishop ,\m.
Editors' note: This manuscript was revised after these
discussions were presented. Discussion DR.JOHNT. QUEENAN, Washington, D.C. In the last 3 years, more than 15 articles have appeared in the literature describing variations on the theme of the nonstress test. The criteria for a favorable or so-called "reactive test" depend upon demonstrating fetal heart rate acceleration generally in response to fetal mm:ement. The minimum criterion for accelerations in some studies is greater than 10 bpm, and in others it is greater than 15 bpm. Some authors require the accelerations to last more than 15 seconds: others do not specify any duration. Some authors permit stimulation of the fetus when the test is nonreactive, and others do not. Some investigators study the fetus for 10 minutes: others. up to 30 minutes. This wide variation of standards for a nonstress test provides so many permutations and combinations that it is almost impossible to compare one series with another. Dr. Bishop's presentation today has shown that fetal reactivity is a function of advancing gestational age. He has shown that this phenomenon pertains in both normal and high-risk pregnancies. Indeed, any attempt to evaluate fetal reactivity prior to 30 weeks' gestation would have very misleading results. In his study he has adapted criteria different from others in the literature. Dr. Bishop requires that fetal heart rate accelerations only be greater than I 0 bpm with no duration of acceleration specified. He requires that there be five accelerations in 30 minutes and additionally that 50% of them must be associated with fetal movement. This does not correspond to the criteria in studies that have prm·ed the efficacy of the nonstress test in decreasing the perinatal mortality rate in large series: therefore, it becomes \·ery difficult to compare his data with those of other studies. Dr. Bishop found that the number of nonreactive tests in the control group was the same as that in the high-risk pregnancy group. The incidence of nonreactive studies was approximately 69{, in both groups. Several authors have shown that the nonstress test is very efficacious in decreasing perinatal mortality in high-risk pregnancies. The findings of the nonstress test are a clinical correlation. Several thousand deliveries are necessary to prove its efficacy. The fact that the rate of nonreactive tests in the control population was similar to that in the high-risk population by no means invalidates the test. If more strict criteria for fetal heart rate accelerations were used, the number of false positive tests would be even higher. The nonstress test is used as a first line of defense in the high-risk pregnancy. The clinician does not act on the nonstress test alone but on other factors such as the clinical course, biochemical monitoring, the oxytocin challenge test, fetal movements, and fetal breathing.
Decernbt·r ! ~). 19K 1 J. Obstet. (;ynt-cnl
Fetal sleep cycles and glucose le\·els affect the nonstress test and must be taken into accol!nt whcu the nonstress test is performed. The high false pm.itive rate is a disadvantage that the clinician must cope with. cl he benefit of the test-the low false negative rate-far outweighs this disadvantage. I would like to ask Dr. Bishop: ( 1) Why did you select these criteria? (2) What was the clinical correlation in terms of morbidity and mortality of the nonreactive nonstress tests? (3) Do you believe your findings would be different if you used more strict criteria to define accelerations? DR. MoRTIMER RoSEN, Cleveland, Ohio. I would like to compliment Dr. Bishop on the work he has presented and comment specifically on two points, the study of the normal population and the study of fetuses in utero prior to 30 weeks. We used similar noniroring techniques and instruments, but the speed of the paper is increased tenfold and the abdominal strain gauge is used at its highest setting, which enables us to determine more dearly the characteristics of the recording. Several investigators, including Dr. Sovolcon, assisted by Dr. Dierker and myself, studied fetuses between 20 and 30 weeks of gestational age. What we found in that population was that after ~0 weeks, when the fetus moves and the movement is more than l second in duration, 90'/f of the time there will be a cardimascular response, and in this normal population that response will be a fetal heart rate acceleration. In marked contrast, prior to 30 weeks of gestation and with e\·en more movement before the twenty-eighth week, half of the time there will he no discernible heart rate change when the fetus moves. Second, and an e\·en more interesting fact, is that before 28 weeks acceleration is not the normal fetal response. Rather there is a fetal heart rate deceleration in almost half of the responses. This would emphasize the second point Dr. Bishop made. If this test is to be used in the less mature fetus, new criteria for a normal nonstress test will have to be obtained. DR. CALVIN HOBEL, Torrance, California. We are now recognizing a difference between the sex of the fetus and maturation and the risk of morbidity and mortality. We are, in a sense. dealing with two populations of patients in the uterus, male and female ones. Dr. Bishop, did you look at the difference between the male fetus and the female fetus in terms of the incidence of nonreactivity? DR. RICHARD PAUL, Los Angeles, California. I noticed that 10 patients were eliminated from the normal group, and I wondered if you might comment on the findings of antepartum monitoring in that particular group of subjects who were dropped and apparently developed some abnormality. DR. BISHOP (Closing). First, Dr. Paul, as far as what happened to the group who were eliminated, there
Volume HI :\umber H
were only I 0 of them and I do not remember how many tests they had, but the numbers were not really significant. They were eliminated for the indications 1 mentioned before. By just looking at them casually there wa~ no particularly different pattern in the number or the frequencv of reactivity or nonreactivity in that group. Whenever one presents a paper the discussants alwavs send one home to do more work. Now I have to go back and look at sex to see if there is any difference. I cannot comment on Dr. Rosen's work except to be fascinated bv his findings. We have had no experience in this area. I share Dr. Queenan's feeling that it is regrettable that we have had no standards to go by. I do not know how many types of nons tress tests there are; I think he mentioned a large number, which is, indeed, a problem. We used the same standard during the entire study. We are not using this standard at the present time since we are using a shorter period of time. When I reread all of these tracings and used the other standards, our results did not change significantly. Occasionally when we used 15 as a standard, one or two were changed as to categorv. In generaL if I had done the analysis with
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these other standards, I believe the result' would have been about the same. However, the alternate interpretive methods would not have been performed blindly. I knew which were normal and abnormal: therefore, I thought we should stay with the original ~tandards. However, I do not reallv think it make, 'en much difference. \Ve. too, were concerned about glucos<, levels, and none of these tests was clone after a period of maternal fasting because that does make a differeun', A recent report indicates that the I 0-minute test may not be long enough. Even the :W-minute test we use may not be long enough. Possibly we should use an hour or an hour and a half because or the time imervals of sleep and activity of the fetus. :Mavbe we han~ erred in using the shorter test rather than the longer one. I do not han~ am: inf(Jrmation on morbidity and mortality. In the high-risk group it appears that a number of the morbidities were predicted, hut there are so many other factors that I cannot :~he a direcr answer to that question. I do not have a follow-up for anv of ;he infants other than at the time or discharge from rhe nurser\.