Oxytocin challenge test ALLAN TAN
B. P.
JANE Washington
WEINGOLD,
M.D.
S. DEJESUS,
O’KEIFFE,
M.D. B.A.
0. c.
This study reviews the indications, interpretation, and practical application of the oxytocin challenge test (XT) in 154 patients undergoing 375 tests. It emphasizes aspects of technique which may make the “challenge” nonphysiologic and the stress, therefore, nonqwmta$able. Thirty-four positive or suspicious tests were obtained in 22 patients. These results are correlated with clinical complications of pregnancy; antepartum indices of fetal well-being (estriol, ultrasonic serial cephalometry, and the presence of meconium on amniocentesis); and subsequent intrapartum fetal heart rate response. Unsatisfactory (47 in 23 patients), false-positive, and false-negative tests are reviewed in detail. Since false-positive tests (47.9 per cent) are common whereas false-negative tests are rare (2.8 per cent), we conclude that the negative test is a reliuble indication in high-risk pregnancies. Positive tests add to our data on the fetus and alert us to the need for a totally monitored labor.
DURING LABOR, late deceleration of the fetal heart rate is associated with signs of fetal distress (uteroplacental insufficiency) such as acidosis, low Apgar scores at birth, and, rarely, intrapartum fetal death. The recognition of this pattern serves as one of the bases for clinical fetal monitoring in parturition. In 1966 Hammacher’ suggested that, in late pregnancy, the response of the fetal heart rate to oxytocin-induced contractions would be a valuable method of predicting the capability of the fetus to withstand the stress of labor. Ray and associates’ outlined the oxytocin challenge test (OCT) procedure and defined a positive test as a uniform deceleration of the fetal heart rate which reflects the wave form of the uterine contraction with onset at or beyond the acme of a contraction and occurring repetitively. They also extended the applicability of the procedure by describing its role in determining both the necessity of and the mode of delivery in an at-risk pregnancy. The present study reviews our own experience with the OCT, stressing its indications, technique, limita-
tions, and intrapartum
correlation monitoring,
with other antepartum and perinatal outcome.
tests,
Matettaland method Oxytocin challenge tests were performed on 154 patients during a 2 year period from July 1, 1972, through June 30, 1974. Indications for the procedure included hypertensive disease in pregnancy, postdatism, diabetes, intrauterine growth retardation, previous late fetal death, previous fetal distress in labor, elderly primigravidity, and a group of apparently normal patients with low 24 hour urinary estriol excretion patterns. Multiple indications existed in more than one third of this group. A total of 375 tests were performed on these 154 patients. The high ratio of tests/patients is explained by the fact that the induction of labor in the majority of patients previously evaluated by an OCT was conducted under test conditions and was recorded as a repeat procedure. More than half of the patients (83/154) had three or more tests performed (Table I). When only a single test was performed either it was positive, and the pregnancy was terminated at the time of or soon after the procedure, or it was negative, late in pregnancy, and was followed by the spontaneous onset of labor. The OCT was conducted with the patient in a 30” semi-Fowler’s position. A slight left lateral tilt was obtained by a foam wedge under the right buttock in an attempt to reduce the incidence of and impact of
From the Departments af Obstetrics and Gynecology, the George Washington Universiby School of Medicine and Health Sciences, and the New York Medical College-Metropolitan Hospital Center. Presented by invitation at the Ninety-eighth Annual Meeting of the American Gynecological Society, Coronado, California, April 9-12, 1975. Reprint requestc: George Washington Universi~ Medical Center, Department of Obstetrics and Gynecology, 2150 Pennsylvania Avenue N.W., Washington D.C. 20037. 466
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supine hypotension. Maternal blood pressure was monitored every 10 minutes before and during the OCT. Patients who were not scheduled for induction were evaluated postprandially since fetal activity appears reduced at this time.2 Monitoring of uterine activity and the fetal heart rate was accomplished with a Corometrics Model number FMS-1OlA fetal monitor. Uterine contractions were assessed by an external tocograph. Initially the fetal heart rate was evaluated via phonocardiogram and subsequently with Doppler ultrasound. Baseline recording continued for a period of 10 to 15 minutes to evaluate the presence of sufficient spontaneous uterine activity to meet the requisites of a uterine stress. The fetal heart rate was also assessed for its baseline rate, the presence of variability, and the occurrence of any periodic deceleration. Marked irregularity in the fetal heart rhythms before the onset of labor, without relationship to contractions, has not been associated with an unfavorable outcome.3 An infusion of 5 per cent dextrose in water was begun via a 2 1 gauge butterfly needle on the dorsum of the hand. Oxytocin was administered by a piggy-back infusion and delivered by pump with a starting dose of 0.5 mu. per minute. This was increased incrementally at 15 minute intervals, with contractions usually apparent at 5 mu. per minute. A maximum dosage of 20 mu. per minute was set in the attempt to avoid hypertonus. At this level the infusion was continued for an additional 30 minutes, in the absence of contractions, before a failed test was concluded. No medication other than oxytocin was utilized. Several patients displayed significant anxiety, particularly at the initial procedure, but sedatives and/or tranquilizing agents were withheld to avoid obtunding fetal response. A positive test was defined as persistent late deceleration of greater than 5 beats per minute from the previous baseline. This narrow limit was set so as to eliminate a false-negative factor in interpretation. Suspicious tests included inconsistent or transient late deceleration, fixed or nonvariable baseline, bradycardia. tachycardia, or “atypical” variable deceleration. The difficulty in classifying tracings obtained by external cardiotachometry is considerable and unquestionably plays a role in the discrepant incidence and predictive values reported. F?SSlh
There were 23 positive tests in 14 patients and 11 suspicious tests in eight patients. Negative tests were recorded 294 times in 100 patients. In 23 patients we were unable to obtain a recordable tracing; in 15
Table
I. Oxytocin
Single test Two testi Three or more Total
Table
challenge
tests
II. Oxytocin
challenge
Indication Hypertensive disease Post-datism Diabetes Growth retardation* Poor obstetric history Total *Without
467
test: frequency Patients
T’ests
27 44 83 154
27 88 --260 :175
test: postive I
testing
incidenc~~ 6168 1131 3127 Pi18 -- 2125 14/154
hypertension.
patients of this group repeat tests (one or more) were also failures. Twenty-six unsatisfactory procedures were ascribed to inadequate contractions (a ceiling on oxytocin dosage was employed); 11 to tracing defects (secondary to obesity, polyhydramnios, maternal or fetal movement, and borborygmi); six to supine hypotension; and four to patient request (anxiety or discomfort due to fixed positioning over time). Review of the major clinical indications for the OCT, and the frequency of positive tests, revealed an approximate 10 per cent incidence in each classification with the exception of post-datism (Table II). The latter category was predominantly without medical complication and associated with a low perinatal risk. The correlation of a positive OCT with other antepartum indices of fetal well-being is more variable (Table III). A low or falling estriol was present in 44 patients, six of whom had a positive OCT. Seventeen of these patients had no clinical abnormality and only one had a positive test. When abnormal estriol excretion was associated with an obstetric complication (27 patients), five positive tests (18.4 per cent) were recorded. Cessation or deceleration of fetal biparietal diameter growth as measured by serial ultrasonograph>, in eight patients was associated with three positive tests. The finding of meconium on amniocentesis before labor was associated with two positive OCT in five patients. The fetal heart rate in subsequent labor was monitored in 131 patients previously screened by OCT. Tracings were complete (onset to vaginal delivery or cesarean section) in 20 of 22 patients with positive or suspicious tests. In the remaining two patients,
466
Weingold, DeJesus, and O’Keiffe
Table III. correlation
Oxytocin
challenge
test: antepartum
Table
V. Oxytocin
Low estriol only All low estriol Positive ultrasound Meconium on amniocentesis
17 44 8 5
1 6 3 2
No.
Negative test (109 patients) Postive test (14 patients) Suspicious test (8 patients) Total *No intrapartum
challenge
test: intrapartum
Abnormal fetal heart rate (%)
Negative test (109) Positive test (14) Suspicious test (8)
test: end results Perinatal deaths *
Positive tests
Patients
Table IV. Oxytocin correlation
challenge
11.0 71.4 37.5
Late decel. only ( %I
2.8 57.1 12.5
monitoring was begun as soon after admission in labor as possible. Thirty-seven cesarean sections were performed (28.3 per cent); none electively. Some period of fetal heart rate tracing was available for each of these patients. Those with prior cesarean sections were eliminated from the study group and are still considered to be an unsafe group for the OCT. The incidence of late deceleration and all other abnormal fetal heart rate patterns related directly to the presence of negative, suspicious, and positive OCT before labor (Table IV). Of the group with negative tests, three patients had late deceleration and nine more had other types of abnormal tracings (early or variable deceleration, loss of beat-to-beat variability, tachycardia, or bradycardia). The OCT appeared to be false negative in only one of those patients with late deceleration. The second patient had injudicious oxytocin administration with hypertonus and the third had a terminal abruptio placentae. Those patients who had suspicious OCT8 subsequently showed one late deceleration pattern and two other heart rate abnormalities. Of the 14 patients with a positive OCT, eight had late deceleration during labor while two patients had other abnormalities. The false-positive rate of the OCT in this study (42.9 per cent) was higher than generally anticipated and may be related to the “closeness” of the tracing evaluation of late deceleration (5 beats per minute drop). There were five perinatal deaths with an over-all uncorrected mortality rate of 32.5/1,000 (Table V).
1 3 1 5
Rate
9.2/ 1,000 214.3/1,000 12511,000 32.511,OOO
deaths.
There was one death in the negative OCT cohort. A 2,060 gram neonate died 2 days after birth following labor not associated with late deceleration. There was one death in the suspicious group, an antepartum death at 34 weeks in a patient with Class C diabetes, 3 days after the test. Estriol levels had been low and the last value obtained 2 days before death was 5.8 mg. per 24 hours. There were three deaths in the positive OCT group. Two antepartum deaths occurred, one at 3 1 weeks in a hypertensive patient and one at 33 weeks in a Class E diabetic patient. Both occurred within 5 days of the positive test. The third was a neonatal death which occurred 4 days after the birth of an 1,845 gram neonate and was ascribed to disseminated intravascular coagulation. There were no intrapartum deaths in the study group, which is probably related to the high frequency of monitoring during labor more than to the predictability of the OCT. Significantly, there were only nine neonates (6.9 per cent) with Apgar scores of 6 or less at 5 minutes. This also suggests the important role of labor monitoring in this group of high-risk patients.
Comment The relative advantages and disadvantages of the OCT have been stressed in a number of recent presentations and publications. 4-7 The procedure is simple to perform but does require a trained perinatal nurse or technician and a physician able to promptly interpret the heart rate tracings. These personnel requirements make the procedure expensive in manpower terms but also provide safeguards against the occasional severe fetal reaction to stress. Position change and oxygen administration following discontinuation of the infusion have generally been promptly effective in restoring normal fetal status. One emergency cesarean section was performed in our series and an additional case has been reported.6 Premature labor did not occur in our study but has been reported by Cooper and associates6 who also noted five instances of uterine hypertonus. Generally all uterine activity subsides to
V&me Number
1% 5
pretest levels within 60 to 90 minutes. One of the outstanding advantages of the OCT is that it can be performed and interpreted instantaneously and repeated at any time. Further, it is performed by the obstetrician who is also aware of the clinical problem. Similarly, and quite importantly, it is relevant to the upcoming clinical events: labor and delivery. On the negative side, in addition to the expense of personnel mentioned above, there is additional cost of equipment and time. Most available fetal monitoring equipment has or can be converted to an external mode. Since we firmly believe that intrapartum monitoring is essential in high-risk pregnancy management, equipment should be available. The time factor is important because the procedure averages 90 minutes and may take considerably longer. This may inconvenience a busy obstetric service unless an ambulatory testing area adjacent to the labor suite is available. Of greater concern is the lingering question as to the physiologic or nonphysiologic nature of the stress induced by the procedure. We have already alluded to the problem of supine hypotension and the necessity for frequent monitoring of maternal blood pressure. Clearly, late deceleration due to hypoperfusion might produce a false positive OCT. An additional problem and an inherent difficulty with external contraction monitoring is the inability to measure the degree of “stress” applied to the fetoplacental unit. A negative OCT with maximum intrauterine pressures of only 15 mm. Hg may have less significance than a test in which pressures are recorded at 35 mm. Hg. Conversely, unrecognized elevations in baseline uterine tone are not measurable by external tocography and may produce false-positive test results. Cooper and associate@ attempted to meet these difficulties by performing transabdominal monitoring between 32 and 44 weeks of pregnancy in 89 high-risk patients. His group introduced a No. 18.5 silicone rubber catheter through a 17-guage Touhey needle for quantifiable uterine pressure recording. Nevertheless, five instances of hypertonus were noted, one requiring emergency cesarean section. Despite meticulous attention to asepsis and ultrasonic placental localization, we are still concerned about an invasive methodology in early or mid thirdtrimester patients. The risk of hypertonus may also be reduced by limiting the procedure to the first 10 minutes of acceptable contractions. The concept of a shortened OCT has been questioned: however, as likely to result in an increase in false-positive tests, particularly in the premature. The smaller fetus may respond, initially and transiently, to hypoxia produced by uterine con-
Oxytocin challenge test
469
tractions with subsequent tracing data returning to normal baseline activity. There appears to be general agreement as to our listed indications for the OCT expressed in all recent report?, 4-8 and also as to the need for repeat tests at about weekly intervals. There is also concurrence with our view that the risk of the procedure, although minimal, makes its application academic before that time in pregnancy when the chance of extrallterine survival is realistic (30 to 32 weeks?). The lack of correlation between estriof level>+ and a positive OCT in our study is disappointing. Kubli and associates9 have suggested that placental function may be divided into two components--“nutritive” and “respiratory.” In the normal patient estriol excretion patterns relate closely to fetal growth and size. In growth retardation, a “nutritive” failure, there is a correlation between the degree of deceleration of fetal growth and the decreased level of estriol excreted. This can be expressed as an estriol index with a prt-dictive value useful for clinical diagnosislO A particular advantage of the OCT is its use in chronic fetal distress (IUGR, hypertension) when abnormally low urinary estriol levels are unusually difficult to interpret. In this clinical situation, the OCT may represent an external method for evaluating the “respiratory” function of the placenta. Uterine contractions, whether sponianeous or oxytocin induced, result in decreased intervillous space blood flow. If the oxygen available in this space is inadequate (a low reserve), placental “respiratl.)ry” insufficiency is expressed as late deceleration of the fetal heart rate. Whether the frequency of late deceleration is influenced by the nature of stimulus or stress (spontaneous contraction or oxytocin induced) is uncertain under the conditions of the test. We have previously noted”-and Schiffrin12 has confirmed--an increased frequency of late deceleration pattern5 in oxytocininduced labors vs. spontaneous uterine activit!‘. The number of patients evaluated in the six previously published reports on the OCT2s *+ tatal 439. There were 12 perinatal deaths described (seven antepartum, five neonatal) for an uncorrected nlortality rate of 27.3/ 1,000. The figure reported in our study of an additional 154 patients is 32.5/1,000. We believe that it is highly significant that no intrapartutn death has been described in any patient whose labor tollowed an OCT, positive or negative. Intensive manitoring and aggressive management of labor proceded by a positive OCT is apparent in all published repc)rts. The ultimate significance of a positive test is still uncertain in our view because of the presence of a significant number of false-positive tests. Nevertheless, the majority of fetuses with a positive OCT will not
470
Weingold, DeJesus, and O’Keiffe
tolerate labor without evidence of uteroplacental insufficiency. Since it is not possible to assess the degree of hypoxia from an abnormal fetal heart rate response, the presence of a positive test should indicate, with few exceptions, the need for delivery without delay. If all of subsequent labor can be monitored (and this can be assured only by induction of labor under OCT conditions) an attempt at vaginal delivery is warranted.
Cesarean section should be immediately available and will be utilized with high frequency. A negative OCT appears to be a generally reliable indicator of fetal well-being in a high-risk pregnancy. The low false-negative rate permits avoidance of premature termination of pregnancy which might be otherwise indicated by clinical signs or by chronically low or falling estriol values.
REFERENCES
1. Hammacher, K.: In Elert, R., and Hates, K. A., editors: Die Prophylaxe Friihkindlicher Hernschsden, Stuttgart, Georg Theime Verlag, p. 120. 2. Ray, M., Freeman, R. K., Pine, S., and Hesselgesser, R.: Clinical experience with the oxytocin challenge test, AM. J. OBSTET. GYNECOL. 114: 1, 1972. 3. Bishop, E. H.: Ultrasonic fetal monitoring, Clin. Obstet. Gynecol. 11: 1154, 1968. 4. Boyd, I. E., Chamberlain, G. V. P., and Ferguson, I. L. C.: The oxytocin stress test and the isoxsuprine placental transfe; test in the management of suspected Placental insufficiencv. I. Obstet. Gvnaecol. Br. Commonw. 81: 120, 1974. ” _ 5. Ewing, D. E., Farina, J. R., and Otterson, N. W.: Clinical application of the oxytocin challenge test, Obstet. Gynecol. 43: 563, 1974. 6. Cooper, J. M., Soffronoff, E. C., and Bolognese, R. J.: Oxytocin challenge test in monitoring high risk pregnancies, Obstet. Gynecol. 45: 27, 1975.
Discussion H. BISHOP, Chapel Hill, North Carolina. The availability of a simple, safe, and reliable test of placental respiratory reserve would be an invaluable addition to the armanentarium of the obstetrician. The OCT may eventually become such a tool but problems still exist with respect to both utilization and evaluation. Paramount among the problems is lack of standardization. Although many individuals have developed standards for their own institution, there is far from universal agreement. Among the questions remaining unanswered are (!) How extensive deceleration is necessary for a diagnosis of late deceleration? Dr. Weingold has chosen “5 beats per minute from the previous baseline.” We not only agree with the author that his high false positive rate may be related to the ‘*closeness” but that, particularly with external monitoring, it is impossible to interpret such a minor change. (2) How frequently should decelerations occur to indicate significant reaction to distress? (3) What is the prognostic relationship between deceleration and lack of baseline variability? (4) What should be the initial rate of administration of oxytocin, how often, and at what increments should this rate be increased? Among the published reports, the initial rate of administration has varied from 0.5 to 2.5 mu. per minute. (5) What constitutes an adequate uterine contraction? What increase of intra-amniotic pressure is significant in causing decreased intervillous blood flow? DR.
EDWARD
7. Christie, G. B., and Cudmore, D. W.: The oxytocin challenge test, AM. 1. OBSTET. GYNECOL. 118: 327, 1974. 8. Spurred, B.: Stressed cardiotocography in late pregnancy, 1. Obstet. Gvnaecol. Br. Commonw. 78: 894. 1971. 9. I&&i, F. W., Kaeser, O., and Henselmann, M.: in Pecile, A., and Finzi, C., editors: The Feto-placental Unit, Amsterdam, 1969, Excerpta Medica Foundation, p. 323. 10. Low, J. A., Galbraith, R. S., and Boston, R. W.: Maternal urinary estrogen patterns in intrauterine growth retardation, dbstet. Gynecol. 42: 325, 1974. 11. Weinnold. A. B.. Feit. A.. O’Sullivan. M. 1.. and Stone. M. L.: Fztal heart rate &I&se in the’pre&tic hyPertensive patient during spontaneous and oxytocin induced labor, J. Reprod. Med. 5: 35, 1970. 12. Schiffrin, B.: Fetal heart rate patterns following epidural anaesthesia and oxytocin infusion during lahour, J. Obstet. Gynaecol. Br. Commonw. 79: 332, 1972.
A second problem is the potential of fetal danger by initiation of an unusual stress from an unexpected reaction of the myometrium to exogenous oxytocin. During the past 6 months this has occurred on at least three occasions in our department. A typical example is shown in Fig. 1, representing a challenge test on an insulin-dependent diabetic patient. Administration of oxytocin was begun at 1 mu. per minute and, after approximately 10 minutes at this rate, a tetanic contraction occurred. This was associated with a long period of bradycardia, which cannot be favorable for the fetus. Schifrin and his co-workers reported nine instances of “excessive uterine activity” (although not defined) in a series of 93 tests resulting in seven instances of transient bradycardia. Cudmore reported nine instances of uterine hypertonia in a series of 60 OCT’s. Four of these were associated with late decelerations. In this latter series, the oxytocin infusion was initiated at 5 mu. per minute, a rate we consider as excessive, and this rate may have been responsible for the number of complications. A final problem is concerned with utilization of results as determinants for management. Opinions in the literature vary from one extreme, advising that a positive OCT be ignored as an unreliable test, to the other extreme, advising that these fetuses with a positive OCT should be delivered at once. The author evidently experienced the same dilemma. Although he states, “The presence of a positive test should indicate
Volume 123 Number 5
Oxytocin
challenge
test
471
Fig, 1. An example of potential fetal danger in the test.
. . the need for delivery without delay,” he cites two antepartum deaths which occurred within 5 days of a positive test. I suspect either there were unstated reasons for these delays or possibly the author’s conclusion was determined only after analysis of the entire series. DR. EDWARD J. QUILLIGAN, Los Angeles, California. Roger Freeman has recently looked at our statistics again in something over 500 patients, and we would agree with the author that there is a fairly high rate of false-positive tests. In our experience, it is not quite as high as his; it is about 25 per cent. And also, I would caution, there are some falsenegative tests. In our own series, we have had three false-negative tests. So, like any other laboratory test, it is not perfect, but when it is negative, I think it can give the obstetrician a large degree of reassurance that perhaps he can wait for one week with good assurance the fetus will not die within that week. We also have the problem of hyperstimulation which, I would agree, is a real problem. In the initial series, our incidence of hyperstimulation was 6 per cent. When Dr. Freeman described the technique that we were using originally, we were increasing the dose of oxytocin every 10 minutes. That is too rapid an increase even when you start it at very low levels. Subsequently, we have modified our technique so we increase the oxytocin only every 15 to 20 minutes. This has reduced our incidence of hyperstimulation from 6 per cent down to something less than 2 per cent. DR. CHARLES E. FLOWERS, JR., Birmingham, Alabama. I rise to support Dr. Weingold’s presentation concerning the OCT. We have performed about 1,000 such tests, utilizing the technique and guidelines of interpretation of Dr. Roger Freeman. We feel this is a most valuable test for an obstetrician. The negative
OCT is allowing us to follow diabetic subjects and patients with severe hypertensive diseases closer to term or to the point that a reasonable L/S ratio ensures the absence of respiratory distress syndrome. This test is also allowing us to treat postdatism without creating iatrogenic errors. We have also found that in some patients who have a positive OCT labor may be successfully induced provided that the Bishop score is favorable, the patient labors on her side, receives continuous oxygen, and is monitored cautiously by internal monitoring. I commend the OCT and the use of the L/S ratio as a combination which has placed obstetrics in the most secure scientific place it has ever had. DR. NICHOLAS S. ASSALI, Los Angeles, California. I have the impression when I listen to these presentations on the OCT that clinicians tend to place the major emphasis when the test is positive or negative on the maternal side of the placental circulation; they neglect to think that the placenta has two sides. As a matter of fact, the fetal side could be just as implicated in fetal distress as the maternal side. There could be .L lot of disturbances on the fetal side which could account for the abnormalities in the estriol excretion because estrio1 precursors come from the fetus. Therefore, it should not be surprising to see disagreements lietween the estriol test and the OCT. So I think it is very important to remember that the placenta has two sides and two independent circulations; fetal distress should not always be attributed to disturbance in the maternal side, it could equally occur with more damaging effects when the problem is on the fetal side of the placenta. DR. WILLIAM N. SPELLACY, Gainesville, Florida. One of the problems in screening large antepartum populations with the OCT is the time and expense required to perform the test. I was interested in the lack of
472
Weingold, DeJesus, and O’Keiffe
correlation between the estriol results and the OCT results and I would like Dr. Weingold to comment on this. We have been studying serum human placental lactogen levels in patients who are also having the OCT and we find a good correlation between the results. A low serum HPL value helps select a population which will have a high frequency of positive OCT results. This simple blood screening test might decrease the need for some OCT studies. DR. WEINGOLD (Closing). I neglected to mention that all patients induced in this study were, of course, evaluated by the Bishop score before labor was induced. I agree that calling a late deceleration at 5 beats per minute is a narrow limit. We use a 3X magnification lens and try to read it as closely as we can. I think from our point of view, in evaluating this procedure, it was important to call as many positives as we could in the beginning before we defined what the limits of readability were. There is no question about the fact that there are a number of difficult readings because of the ultrasound tracing. Many of these patients that we perhaps discard as unreadable might be read by others. But, on the other hand, I think we are calling some positives that are probably overcalled. We do not believe that the procedure should be utilized in patients with prior cesarean section since we do have concern over its safety. We have not had the specific problem of hypertonus, but I think that is because we have noted, in a previous study, the sensitivity of the uterus in the hypertensive patients to what are generally physiologic levels of oxytocin. I think it is extremely important to start at minimal doses and to increment slowly. And as Dr. Quilligan suggests, at 20 mu. or more, observing the interval between contractions may be appropriate. We also put a finite cutoff point on the oxytocin dosage. The question of termination of pregnancy after a positive test is a difficult one. Both of our antepartum fetal deaths with a positive test were significantly premature, 31 and 33 weeks, with negative L/S ratios. I
think we are still on the horns of a dilemma there as to whether, with a negative L/S ratio and positive OCT, one moves to termination. My current feeling would be negative. The patient should be hospitalized, repetitively stress tested, and monitored by daily estriols while awaiting maturity. This, of course, is the group where, at least by Liggins’ recommendation, you would be least likely to use corticosteroids to induce pulmonary maturation because of the hypertensive background. I think, Dr. Quilligan, in answer to the problem of hyperstimulation, I would only stress the importance of a reasonable baseline observation period to look for spontaneous activity. Many of these patients in the high-risk situation have motile, very active, uteri and are contracting with enough frequency to give you some data to look at without adding oxytocin. I have to acknowledge that I received a letter from Dr. Flowers’ department asking me for some advice on the OCT. The letter indicated that Dr. Flowers’ service had done 1,000 tests in the past 6 months or so. I felt rather subdued by the volume of the work being done there. Dr. Assali, I think the question on the fetal side is a very appropriate one. If this test has a unique application, it is in the intrauterine growth-retarded fetus where you have chronically low estriols, and you have difficulty in using this endocrine index as a measurement of fetal status. In this group, the OCT may give some measurement of the respiratory reserve and separate out the fetus that is having an intrinsic problem. Finally, we do not measure HPL, and I think it is a very excellent idea to have a screening tool to sort out those patients who would require the OCT. It is a time-consuming procedure. Certainly, if estriol falls after the OCT becomes positive, which is what Dr. Freeman indicates to be true, estriol cannot be utilized as a screening tool which, in a sense, we did in our study. Measurement of HPL may be an important contribution there.
B. P.
JANE Washington
WEINGOLD,
M.D.
S. DEJESUS,
O’KEIFFE,
M.D. B.A.
0. c.
This study reviews the indications, interpretation, and practical application of the oxytocin challenge test (XT) in 154 patients undergoing 375 tests. It emphasizes aspects of technique which may make the “challenge” nonphysiologic and the stress, therefore, nonqwmta$able. Thirty-four positive or suspicious tests were obtained in 22 patients. These results are correlated with clinical complications of pregnancy; antepartum indices of fetal well-being (estriol, ultrasonic serial cephalometry, and the presence of meconium on amniocentesis); and subsequent intrapartum fetal heart rate response. Unsatisfactory (47 in 23 patients), false-positive, and false-negative tests are reviewed in detail. Since false-positive tests (47.9 per cent) are common whereas false-negative tests are rare (2.8 per cent), we conclude that the negative test is a reliuble indication in high-risk pregnancies. Positive tests add to our data on the fetus and alert us to the need for a totally monitored labor.
DURING LABOR, late deceleration of the fetal heart rate is associated with signs of fetal distress (uteroplacental insufficiency) such as acidosis, low Apgar scores at birth, and, rarely, intrapartum fetal death. The recognition of this pattern serves as one of the bases for clinical fetal monitoring in parturition. In 1966 Hammacher’ suggested that, in late pregnancy, the response of the fetal heart rate to oxytocin-induced contractions would be a valuable method of predicting the capability of the fetus to withstand the stress of labor. Ray and associates’ outlined the oxytocin challenge test (OCT) procedure and defined a positive test as a uniform deceleration of the fetal heart rate which reflects the wave form of the uterine contraction with onset at or beyond the acme of a contraction and occurring repetitively. They also extended the applicability of the procedure by describing its role in determining both the necessity of and the mode of delivery in an at-risk pregnancy. The present study reviews our own experience with the OCT, stressing its indications, technique, limita-
tions, and intrapartum
correlation monitoring,
with other antepartum and perinatal outcome.
tests,
Matettaland method Oxytocin challenge tests were performed on 154 patients during a 2 year period from July 1, 1972, through June 30, 1974. Indications for the procedure included hypertensive disease in pregnancy, postdatism, diabetes, intrauterine growth retardation, previous late fetal death, previous fetal distress in labor, elderly primigravidity, and a group of apparently normal patients with low 24 hour urinary estriol excretion patterns. Multiple indications existed in more than one third of this group. A total of 375 tests were performed on these 154 patients. The high ratio of tests/patients is explained by the fact that the induction of labor in the majority of patients previously evaluated by an OCT was conducted under test conditions and was recorded as a repeat procedure. More than half of the patients (83/154) had three or more tests performed (Table I). When only a single test was performed either it was positive, and the pregnancy was terminated at the time of or soon after the procedure, or it was negative, late in pregnancy, and was followed by the spontaneous onset of labor. The OCT was conducted with the patient in a 30” semi-Fowler’s position. A slight left lateral tilt was obtained by a foam wedge under the right buttock in an attempt to reduce the incidence of and impact of
From the Departments af Obstetrics and Gynecology, the George Washington Universiby School of Medicine and Health Sciences, and the New York Medical College-Metropolitan Hospital Center. Presented by invitation at the Ninety-eighth Annual Meeting of the American Gynecological Society, Coronado, California, April 9-12, 1975. Reprint requestc: George Washington Universi~ Medical Center, Department of Obstetrics and Gynecology, 2150 Pennsylvania Avenue N.W., Washington D.C. 20037. 466
Volume Number
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supine hypotension. Maternal blood pressure was monitored every 10 minutes before and during the OCT. Patients who were not scheduled for induction were evaluated postprandially since fetal activity appears reduced at this time.2 Monitoring of uterine activity and the fetal heart rate was accomplished with a Corometrics Model number FMS-1OlA fetal monitor. Uterine contractions were assessed by an external tocograph. Initially the fetal heart rate was evaluated via phonocardiogram and subsequently with Doppler ultrasound. Baseline recording continued for a period of 10 to 15 minutes to evaluate the presence of sufficient spontaneous uterine activity to meet the requisites of a uterine stress. The fetal heart rate was also assessed for its baseline rate, the presence of variability, and the occurrence of any periodic deceleration. Marked irregularity in the fetal heart rhythms before the onset of labor, without relationship to contractions, has not been associated with an unfavorable outcome.3 An infusion of 5 per cent dextrose in water was begun via a 2 1 gauge butterfly needle on the dorsum of the hand. Oxytocin was administered by a piggy-back infusion and delivered by pump with a starting dose of 0.5 mu. per minute. This was increased incrementally at 15 minute intervals, with contractions usually apparent at 5 mu. per minute. A maximum dosage of 20 mu. per minute was set in the attempt to avoid hypertonus. At this level the infusion was continued for an additional 30 minutes, in the absence of contractions, before a failed test was concluded. No medication other than oxytocin was utilized. Several patients displayed significant anxiety, particularly at the initial procedure, but sedatives and/or tranquilizing agents were withheld to avoid obtunding fetal response. A positive test was defined as persistent late deceleration of greater than 5 beats per minute from the previous baseline. This narrow limit was set so as to eliminate a false-negative factor in interpretation. Suspicious tests included inconsistent or transient late deceleration, fixed or nonvariable baseline, bradycardia. tachycardia, or “atypical” variable deceleration. The difficulty in classifying tracings obtained by external cardiotachometry is considerable and unquestionably plays a role in the discrepant incidence and predictive values reported. F?SSlh
There were 23 positive tests in 14 patients and 11 suspicious tests in eight patients. Negative tests were recorded 294 times in 100 patients. In 23 patients we were unable to obtain a recordable tracing; in 15
Table
I. Oxytocin
Single test Two testi Three or more Total
Table
challenge
tests
II. Oxytocin
challenge
Indication Hypertensive disease Post-datism Diabetes Growth retardation* Poor obstetric history Total *Without
467
test: frequency Patients
T’ests
27 44 83 154
27 88 --260 :175
test: postive I
testing
incidenc~~ 6168 1131 3127 Pi18 -- 2125 14/154
hypertension.
patients of this group repeat tests (one or more) were also failures. Twenty-six unsatisfactory procedures were ascribed to inadequate contractions (a ceiling on oxytocin dosage was employed); 11 to tracing defects (secondary to obesity, polyhydramnios, maternal or fetal movement, and borborygmi); six to supine hypotension; and four to patient request (anxiety or discomfort due to fixed positioning over time). Review of the major clinical indications for the OCT, and the frequency of positive tests, revealed an approximate 10 per cent incidence in each classification with the exception of post-datism (Table II). The latter category was predominantly without medical complication and associated with a low perinatal risk. The correlation of a positive OCT with other antepartum indices of fetal well-being is more variable (Table III). A low or falling estriol was present in 44 patients, six of whom had a positive OCT. Seventeen of these patients had no clinical abnormality and only one had a positive test. When abnormal estriol excretion was associated with an obstetric complication (27 patients), five positive tests (18.4 per cent) were recorded. Cessation or deceleration of fetal biparietal diameter growth as measured by serial ultrasonograph>, in eight patients was associated with three positive tests. The finding of meconium on amniocentesis before labor was associated with two positive OCT in five patients. The fetal heart rate in subsequent labor was monitored in 131 patients previously screened by OCT. Tracings were complete (onset to vaginal delivery or cesarean section) in 20 of 22 patients with positive or suspicious tests. In the remaining two patients,
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Table III. correlation
Oxytocin
challenge
test: antepartum
Table
V. Oxytocin
Low estriol only All low estriol Positive ultrasound Meconium on amniocentesis
17 44 8 5
1 6 3 2
No.
Negative test (109 patients) Postive test (14 patients) Suspicious test (8 patients) Total *No intrapartum
challenge
test: intrapartum
Abnormal fetal heart rate (%)
Negative test (109) Positive test (14) Suspicious test (8)
test: end results Perinatal deaths *
Positive tests
Patients
Table IV. Oxytocin correlation
challenge
11.0 71.4 37.5
Late decel. only ( %I
2.8 57.1 12.5
monitoring was begun as soon after admission in labor as possible. Thirty-seven cesarean sections were performed (28.3 per cent); none electively. Some period of fetal heart rate tracing was available for each of these patients. Those with prior cesarean sections were eliminated from the study group and are still considered to be an unsafe group for the OCT. The incidence of late deceleration and all other abnormal fetal heart rate patterns related directly to the presence of negative, suspicious, and positive OCT before labor (Table IV). Of the group with negative tests, three patients had late deceleration and nine more had other types of abnormal tracings (early or variable deceleration, loss of beat-to-beat variability, tachycardia, or bradycardia). The OCT appeared to be false negative in only one of those patients with late deceleration. The second patient had injudicious oxytocin administration with hypertonus and the third had a terminal abruptio placentae. Those patients who had suspicious OCT8 subsequently showed one late deceleration pattern and two other heart rate abnormalities. Of the 14 patients with a positive OCT, eight had late deceleration during labor while two patients had other abnormalities. The false-positive rate of the OCT in this study (42.9 per cent) was higher than generally anticipated and may be related to the “closeness” of the tracing evaluation of late deceleration (5 beats per minute drop). There were five perinatal deaths with an over-all uncorrected mortality rate of 32.5/1,000 (Table V).
1 3 1 5
Rate
9.2/ 1,000 214.3/1,000 12511,000 32.511,OOO
deaths.
There was one death in the negative OCT cohort. A 2,060 gram neonate died 2 days after birth following labor not associated with late deceleration. There was one death in the suspicious group, an antepartum death at 34 weeks in a patient with Class C diabetes, 3 days after the test. Estriol levels had been low and the last value obtained 2 days before death was 5.8 mg. per 24 hours. There were three deaths in the positive OCT group. Two antepartum deaths occurred, one at 3 1 weeks in a hypertensive patient and one at 33 weeks in a Class E diabetic patient. Both occurred within 5 days of the positive test. The third was a neonatal death which occurred 4 days after the birth of an 1,845 gram neonate and was ascribed to disseminated intravascular coagulation. There were no intrapartum deaths in the study group, which is probably related to the high frequency of monitoring during labor more than to the predictability of the OCT. Significantly, there were only nine neonates (6.9 per cent) with Apgar scores of 6 or less at 5 minutes. This also suggests the important role of labor monitoring in this group of high-risk patients.
Comment The relative advantages and disadvantages of the OCT have been stressed in a number of recent presentations and publications. 4-7 The procedure is simple to perform but does require a trained perinatal nurse or technician and a physician able to promptly interpret the heart rate tracings. These personnel requirements make the procedure expensive in manpower terms but also provide safeguards against the occasional severe fetal reaction to stress. Position change and oxygen administration following discontinuation of the infusion have generally been promptly effective in restoring normal fetal status. One emergency cesarean section was performed in our series and an additional case has been reported.6 Premature labor did not occur in our study but has been reported by Cooper and associates6 who also noted five instances of uterine hypertonus. Generally all uterine activity subsides to
V&me Number
1% 5
pretest levels within 60 to 90 minutes. One of the outstanding advantages of the OCT is that it can be performed and interpreted instantaneously and repeated at any time. Further, it is performed by the obstetrician who is also aware of the clinical problem. Similarly, and quite importantly, it is relevant to the upcoming clinical events: labor and delivery. On the negative side, in addition to the expense of personnel mentioned above, there is additional cost of equipment and time. Most available fetal monitoring equipment has or can be converted to an external mode. Since we firmly believe that intrapartum monitoring is essential in high-risk pregnancy management, equipment should be available. The time factor is important because the procedure averages 90 minutes and may take considerably longer. This may inconvenience a busy obstetric service unless an ambulatory testing area adjacent to the labor suite is available. Of greater concern is the lingering question as to the physiologic or nonphysiologic nature of the stress induced by the procedure. We have already alluded to the problem of supine hypotension and the necessity for frequent monitoring of maternal blood pressure. Clearly, late deceleration due to hypoperfusion might produce a false positive OCT. An additional problem and an inherent difficulty with external contraction monitoring is the inability to measure the degree of “stress” applied to the fetoplacental unit. A negative OCT with maximum intrauterine pressures of only 15 mm. Hg may have less significance than a test in which pressures are recorded at 35 mm. Hg. Conversely, unrecognized elevations in baseline uterine tone are not measurable by external tocography and may produce false-positive test results. Cooper and associate@ attempted to meet these difficulties by performing transabdominal monitoring between 32 and 44 weeks of pregnancy in 89 high-risk patients. His group introduced a No. 18.5 silicone rubber catheter through a 17-guage Touhey needle for quantifiable uterine pressure recording. Nevertheless, five instances of hypertonus were noted, one requiring emergency cesarean section. Despite meticulous attention to asepsis and ultrasonic placental localization, we are still concerned about an invasive methodology in early or mid thirdtrimester patients. The risk of hypertonus may also be reduced by limiting the procedure to the first 10 minutes of acceptable contractions. The concept of a shortened OCT has been questioned: however, as likely to result in an increase in false-positive tests, particularly in the premature. The smaller fetus may respond, initially and transiently, to hypoxia produced by uterine con-
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469
tractions with subsequent tracing data returning to normal baseline activity. There appears to be general agreement as to our listed indications for the OCT expressed in all recent report?, 4-8 and also as to the need for repeat tests at about weekly intervals. There is also concurrence with our view that the risk of the procedure, although minimal, makes its application academic before that time in pregnancy when the chance of extrallterine survival is realistic (30 to 32 weeks?). The lack of correlation between estriof level>+ and a positive OCT in our study is disappointing. Kubli and associates9 have suggested that placental function may be divided into two components--“nutritive” and “respiratory.” In the normal patient estriol excretion patterns relate closely to fetal growth and size. In growth retardation, a “nutritive” failure, there is a correlation between the degree of deceleration of fetal growth and the decreased level of estriol excreted. This can be expressed as an estriol index with a prt-dictive value useful for clinical diagnosislO A particular advantage of the OCT is its use in chronic fetal distress (IUGR, hypertension) when abnormally low urinary estriol levels are unusually difficult to interpret. In this clinical situation, the OCT may represent an external method for evaluating the “respiratory” function of the placenta. Uterine contractions, whether sponianeous or oxytocin induced, result in decreased intervillous space blood flow. If the oxygen available in this space is inadequate (a low reserve), placental “respiratl.)ry” insufficiency is expressed as late deceleration of the fetal heart rate. Whether the frequency of late deceleration is influenced by the nature of stimulus or stress (spontaneous contraction or oxytocin induced) is uncertain under the conditions of the test. We have previously noted”-and Schiffrin12 has confirmed--an increased frequency of late deceleration pattern5 in oxytocininduced labors vs. spontaneous uterine activit!‘. The number of patients evaluated in the six previously published reports on the OCT2s *+ tatal 439. There were 12 perinatal deaths described (seven antepartum, five neonatal) for an uncorrected nlortality rate of 27.3/ 1,000. The figure reported in our study of an additional 154 patients is 32.5/1,000. We believe that it is highly significant that no intrapartutn death has been described in any patient whose labor tollowed an OCT, positive or negative. Intensive manitoring and aggressive management of labor proceded by a positive OCT is apparent in all published repc)rts. The ultimate significance of a positive test is still uncertain in our view because of the presence of a significant number of false-positive tests. Nevertheless, the majority of fetuses with a positive OCT will not
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Weingold, DeJesus, and O’Keiffe
tolerate labor without evidence of uteroplacental insufficiency. Since it is not possible to assess the degree of hypoxia from an abnormal fetal heart rate response, the presence of a positive test should indicate, with few exceptions, the need for delivery without delay. If all of subsequent labor can be monitored (and this can be assured only by induction of labor under OCT conditions) an attempt at vaginal delivery is warranted.
Cesarean section should be immediately available and will be utilized with high frequency. A negative OCT appears to be a generally reliable indicator of fetal well-being in a high-risk pregnancy. The low false-negative rate permits avoidance of premature termination of pregnancy which might be otherwise indicated by clinical signs or by chronically low or falling estriol values.
REFERENCES
1. Hammacher, K.: In Elert, R., and Hates, K. A., editors: Die Prophylaxe Friihkindlicher Hernschsden, Stuttgart, Georg Theime Verlag, p. 120. 2. Ray, M., Freeman, R. K., Pine, S., and Hesselgesser, R.: Clinical experience with the oxytocin challenge test, AM. J. OBSTET. GYNECOL. 114: 1, 1972. 3. Bishop, E. H.: Ultrasonic fetal monitoring, Clin. Obstet. Gynecol. 11: 1154, 1968. 4. Boyd, I. E., Chamberlain, G. V. P., and Ferguson, I. L. C.: The oxytocin stress test and the isoxsuprine placental transfe; test in the management of suspected Placental insufficiencv. I. Obstet. Gvnaecol. Br. Commonw. 81: 120, 1974. ” _ 5. Ewing, D. E., Farina, J. R., and Otterson, N. W.: Clinical application of the oxytocin challenge test, Obstet. Gynecol. 43: 563, 1974. 6. Cooper, J. M., Soffronoff, E. C., and Bolognese, R. J.: Oxytocin challenge test in monitoring high risk pregnancies, Obstet. Gynecol. 45: 27, 1975.
Discussion H. BISHOP, Chapel Hill, North Carolina. The availability of a simple, safe, and reliable test of placental respiratory reserve would be an invaluable addition to the armanentarium of the obstetrician. The OCT may eventually become such a tool but problems still exist with respect to both utilization and evaluation. Paramount among the problems is lack of standardization. Although many individuals have developed standards for their own institution, there is far from universal agreement. Among the questions remaining unanswered are (!) How extensive deceleration is necessary for a diagnosis of late deceleration? Dr. Weingold has chosen “5 beats per minute from the previous baseline.” We not only agree with the author that his high false positive rate may be related to the ‘*closeness” but that, particularly with external monitoring, it is impossible to interpret such a minor change. (2) How frequently should decelerations occur to indicate significant reaction to distress? (3) What is the prognostic relationship between deceleration and lack of baseline variability? (4) What should be the initial rate of administration of oxytocin, how often, and at what increments should this rate be increased? Among the published reports, the initial rate of administration has varied from 0.5 to 2.5 mu. per minute. (5) What constitutes an adequate uterine contraction? What increase of intra-amniotic pressure is significant in causing decreased intervillous blood flow? DR.
EDWARD
7. Christie, G. B., and Cudmore, D. W.: The oxytocin challenge test, AM. 1. OBSTET. GYNECOL. 118: 327, 1974. 8. Spurred, B.: Stressed cardiotocography in late pregnancy, 1. Obstet. Gvnaecol. Br. Commonw. 78: 894. 1971. 9. I&&i, F. W., Kaeser, O., and Henselmann, M.: in Pecile, A., and Finzi, C., editors: The Feto-placental Unit, Amsterdam, 1969, Excerpta Medica Foundation, p. 323. 10. Low, J. A., Galbraith, R. S., and Boston, R. W.: Maternal urinary estrogen patterns in intrauterine growth retardation, dbstet. Gynecol. 42: 325, 1974. 11. Weinnold. A. B.. Feit. A.. O’Sullivan. M. 1.. and Stone. M. L.: Fztal heart rate &I&se in the’pre&tic hyPertensive patient during spontaneous and oxytocin induced labor, J. Reprod. Med. 5: 35, 1970. 12. Schiffrin, B.: Fetal heart rate patterns following epidural anaesthesia and oxytocin infusion during lahour, J. Obstet. Gynaecol. Br. Commonw. 79: 332, 1972.
A second problem is the potential of fetal danger by initiation of an unusual stress from an unexpected reaction of the myometrium to exogenous oxytocin. During the past 6 months this has occurred on at least three occasions in our department. A typical example is shown in Fig. 1, representing a challenge test on an insulin-dependent diabetic patient. Administration of oxytocin was begun at 1 mu. per minute and, after approximately 10 minutes at this rate, a tetanic contraction occurred. This was associated with a long period of bradycardia, which cannot be favorable for the fetus. Schifrin and his co-workers reported nine instances of “excessive uterine activity” (although not defined) in a series of 93 tests resulting in seven instances of transient bradycardia. Cudmore reported nine instances of uterine hypertonia in a series of 60 OCT’s. Four of these were associated with late decelerations. In this latter series, the oxytocin infusion was initiated at 5 mu. per minute, a rate we consider as excessive, and this rate may have been responsible for the number of complications. A final problem is concerned with utilization of results as determinants for management. Opinions in the literature vary from one extreme, advising that a positive OCT be ignored as an unreliable test, to the other extreme, advising that these fetuses with a positive OCT should be delivered at once. The author evidently experienced the same dilemma. Although he states, “The presence of a positive test should indicate
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471
Fig, 1. An example of potential fetal danger in the test.
. . the need for delivery without delay,” he cites two antepartum deaths which occurred within 5 days of a positive test. I suspect either there were unstated reasons for these delays or possibly the author’s conclusion was determined only after analysis of the entire series. DR. EDWARD J. QUILLIGAN, Los Angeles, California. Roger Freeman has recently looked at our statistics again in something over 500 patients, and we would agree with the author that there is a fairly high rate of false-positive tests. In our experience, it is not quite as high as his; it is about 25 per cent. And also, I would caution, there are some falsenegative tests. In our own series, we have had three false-negative tests. So, like any other laboratory test, it is not perfect, but when it is negative, I think it can give the obstetrician a large degree of reassurance that perhaps he can wait for one week with good assurance the fetus will not die within that week. We also have the problem of hyperstimulation which, I would agree, is a real problem. In the initial series, our incidence of hyperstimulation was 6 per cent. When Dr. Freeman described the technique that we were using originally, we were increasing the dose of oxytocin every 10 minutes. That is too rapid an increase even when you start it at very low levels. Subsequently, we have modified our technique so we increase the oxytocin only every 15 to 20 minutes. This has reduced our incidence of hyperstimulation from 6 per cent down to something less than 2 per cent. DR. CHARLES E. FLOWERS, JR., Birmingham, Alabama. I rise to support Dr. Weingold’s presentation concerning the OCT. We have performed about 1,000 such tests, utilizing the technique and guidelines of interpretation of Dr. Roger Freeman. We feel this is a most valuable test for an obstetrician. The negative
OCT is allowing us to follow diabetic subjects and patients with severe hypertensive diseases closer to term or to the point that a reasonable L/S ratio ensures the absence of respiratory distress syndrome. This test is also allowing us to treat postdatism without creating iatrogenic errors. We have also found that in some patients who have a positive OCT labor may be successfully induced provided that the Bishop score is favorable, the patient labors on her side, receives continuous oxygen, and is monitored cautiously by internal monitoring. I commend the OCT and the use of the L/S ratio as a combination which has placed obstetrics in the most secure scientific place it has ever had. DR. NICHOLAS S. ASSALI, Los Angeles, California. I have the impression when I listen to these presentations on the OCT that clinicians tend to place the major emphasis when the test is positive or negative on the maternal side of the placental circulation; they neglect to think that the placenta has two sides. As a matter of fact, the fetal side could be just as implicated in fetal distress as the maternal side. There could be .L lot of disturbances on the fetal side which could account for the abnormalities in the estriol excretion because estrio1 precursors come from the fetus. Therefore, it should not be surprising to see disagreements lietween the estriol test and the OCT. So I think it is very important to remember that the placenta has two sides and two independent circulations; fetal distress should not always be attributed to disturbance in the maternal side, it could equally occur with more damaging effects when the problem is on the fetal side of the placenta. DR. WILLIAM N. SPELLACY, Gainesville, Florida. One of the problems in screening large antepartum populations with the OCT is the time and expense required to perform the test. I was interested in the lack of
472
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correlation between the estriol results and the OCT results and I would like Dr. Weingold to comment on this. We have been studying serum human placental lactogen levels in patients who are also having the OCT and we find a good correlation between the results. A low serum HPL value helps select a population which will have a high frequency of positive OCT results. This simple blood screening test might decrease the need for some OCT studies. DR. WEINGOLD (Closing). I neglected to mention that all patients induced in this study were, of course, evaluated by the Bishop score before labor was induced. I agree that calling a late deceleration at 5 beats per minute is a narrow limit. We use a 3X magnification lens and try to read it as closely as we can. I think from our point of view, in evaluating this procedure, it was important to call as many positives as we could in the beginning before we defined what the limits of readability were. There is no question about the fact that there are a number of difficult readings because of the ultrasound tracing. Many of these patients that we perhaps discard as unreadable might be read by others. But, on the other hand, I think we are calling some positives that are probably overcalled. We do not believe that the procedure should be utilized in patients with prior cesarean section since we do have concern over its safety. We have not had the specific problem of hypertonus, but I think that is because we have noted, in a previous study, the sensitivity of the uterus in the hypertensive patients to what are generally physiologic levels of oxytocin. I think it is extremely important to start at minimal doses and to increment slowly. And as Dr. Quilligan suggests, at 20 mu. or more, observing the interval between contractions may be appropriate. We also put a finite cutoff point on the oxytocin dosage. The question of termination of pregnancy after a positive test is a difficult one. Both of our antepartum fetal deaths with a positive test were significantly premature, 31 and 33 weeks, with negative L/S ratios. I
think we are still on the horns of a dilemma there as to whether, with a negative L/S ratio and positive OCT, one moves to termination. My current feeling would be negative. The patient should be hospitalized, repetitively stress tested, and monitored by daily estriols while awaiting maturity. This, of course, is the group where, at least by Liggins’ recommendation, you would be least likely to use corticosteroids to induce pulmonary maturation because of the hypertensive background. I think, Dr. Quilligan, in answer to the problem of hyperstimulation, I would only stress the importance of a reasonable baseline observation period to look for spontaneous activity. Many of these patients in the high-risk situation have motile, very active, uteri and are contracting with enough frequency to give you some data to look at without adding oxytocin. I have to acknowledge that I received a letter from Dr. Flowers’ department asking me for some advice on the OCT. The letter indicated that Dr. Flowers’ service had done 1,000 tests in the past 6 months or so. I felt rather subdued by the volume of the work being done there. Dr. Assali, I think the question on the fetal side is a very appropriate one. If this test has a unique application, it is in the intrauterine growth-retarded fetus where you have chronically low estriols, and you have difficulty in using this endocrine index as a measurement of fetal status. In this group, the OCT may give some measurement of the respiratory reserve and separate out the fetus that is having an intrinsic problem. Finally, we do not measure HPL, and I think it is a very excellent idea to have a screening tool to sort out those patients who would require the OCT. It is a time-consuming procedure. Certainly, if estriol falls after the OCT becomes positive, which is what Dr. Freeman indicates to be true, estriol cannot be utilized as a screening tool which, in a sense, we did in our study. Measurement of HPL may be an important contribution there.
