British Journal of Obstetrics and Gynaecology January, 1977. Vol84. pp 3 9 4 3
THE OXYTOCIN CHALLENGE TEST AND ANTEPARTUM FETAL ASSESSMENT BY
T. F. BASKETT, Assistant Professor AND
E. A. SANDY,Assistant Head Nurse Department of Obstetrics and Gynaecology, The University of Manitoba and Women's Health Sciences Centre, Winnipeg, Manitoba, R3E 0 2 3 , Canada Summary The oxytocin challenge test (OCT) was performed 537 times on 364 high-risk patients over a three-year period. It was shown that a positive test had a highly significant correlation with a worsened perinatal outcome as measured by stillbirth rate, fetal distress in labour, intrauterine growth retardation, Apgar scores and the need for neonatal resuscitation and intensive care. However, one-third of positive tests were falsely positive when tested by labour. A negative test proved reassuring for a further week of intrauterine life in 98.2 per cent of cases. The role of the OCT in antepartum fetal monitoring is discussed. have reduced placental function. Many of the patients had several complicating factors, but the main indications for performing the test are listed in Table I. The tests were performed on the antenatal ward along the lines outlined by Ray et a1 (1972). The patient was placed in the semirecumbent position and a Corometrics Fetal Monitor lOlB or 111 with external tocography and ultrasound was used to record the uterine activity and fetal heart. After a 15 to 20 minute baseline recording, intravenous oxytocin was infused until contractions were occurring every 3 to 4 minutes. The fetal heart was then assessed over ten contractions. The interpretation of the test was as follows: 1. A negative test showed normal baseline variability and no decelerations of the fetal heart. In addition those tests with either early or intermittent variable decelerations were classified as negative. 2. A positive test was characterized by repeated (three or more consecutive) late decelerations (Hon, 1967).
ITis a decade since Hammacher (1966) suggested assessing the response of the fetal heart to oxytocin-induced contractions in high risk antepartum patients. The rationale is that even mild uterine contractions might induce hypoxia and late deceleration of the fetal heart rate if there is critical reduction of placental function. A number of authors (Kubli et al, 1969; Spurrett, 1971; Ray et al, 1972; Ewing et al, 1974; Schifrin et al, 1975; Cooper et al, 1975) have studied the value of the oxytocin challenge test (OCT) as a guide to the timing and mode of delivery in high-risk pregnancies. Most of these have involved relatively small numbers of patients and the conclusions as to the value and meaning of a positive test have varied. The purpose of this paper is to review a threeyear experience with the OCT in antepartum fetal assessment. METHODS The patients selected were those whose clinical condition made them more likely to 39
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BASKETT AND SANDY
TABLE I Indications for performing oxytocin challenge test
TABLE I1 Oxytocin challenge test-fetal heart patterns obtained in 537 tests
Per cent
Per cent
~~
Pre-eclampsia Small-for-dates Prolonged pregnancy (42 weeks +) Chronic hypertension Diabetes mellitus Gestational diabetes Bad obstetrical history Elderly primigravida Others
38.9 15.1 11.8 8.4 1.4 6.0 5.8
2.2 4.4
3. A suspicious test was defined as one in which any of the following patterns occurred: persistent baseline tachycardia (more than 160 beats/minute), bradycardia (less than 120 beats/minute) or reduced variability (less than 5 beats/minute): repeated (three or more consecutive) variable decelerations or intermittent late decelerations. If negative, the test was repeated at weekly intervals until delivery. If suspicious or positive, the test was repeated in 24 to 48 hours, unless delivery of the patient was undertaken. Where possible, the fetal heart was continuously monitored in labour and this was achieved in 82 per cent of patients. The result of the OCT was correlated with the following factors : intrapartum meconium staining, repeated late decelerations during the last hour of labour, the one and five minute Apgar scores, intrauterine growth retardation (less than 10th centile, Pusey and Haworth, 1969), the need for neonatal resuscitation (defined as intubation and beyond), the need for admission to the neonatal intensive care unit, and the stillbirth and neonatal death rates.
RESULTS There were 537 satisfactory tests performed on 364 patients over the three-year period 1973 to 1975. The number of tests performed on a patient ranged from one to eight. The type and frequency of fetal heart patterns obtained are shown in Table 11. Of all the patients, 299 (82.2 per cent) had only negative tests, 38 (10.4 per cent) had a suspicious test and 27 (7.4 per cent) had a positive test result.
Rate Normal Bradycardia Tachycardia Baseline variability Normal Reduced Decelerations Early Variable intermittent Variable repetitive Late intermittent Late repetitive (Positive test)
98.5 0.9 0.6 96.3 3.1 2.4 15.5 1.1 5.0 6.9
The correlation of the patients with the three different test results and the perinatal outcome is shown in Table Ill. It is obvious that those patients with a positive OCT had the worst perinatal outcome. When the patients with positive tests were compared to those with negative and suspicious results the differences were statistically significant (p
THE OXYTOCIN CHALLENGE TEST AND ANTEPARTUM FETAL ASSESSMENT BY
T. F. BASKETT, Assistant Professor AND
E. A. SANDY,Assistant Head Nurse Department of Obstetrics and Gynaecology, The University of Manitoba and Women's Health Sciences Centre, Winnipeg, Manitoba, R3E 0 2 3 , Canada Summary The oxytocin challenge test (OCT) was performed 537 times on 364 high-risk patients over a three-year period. It was shown that a positive test had a highly significant correlation with a worsened perinatal outcome as measured by stillbirth rate, fetal distress in labour, intrauterine growth retardation, Apgar scores and the need for neonatal resuscitation and intensive care. However, one-third of positive tests were falsely positive when tested by labour. A negative test proved reassuring for a further week of intrauterine life in 98.2 per cent of cases. The role of the OCT in antepartum fetal monitoring is discussed. have reduced placental function. Many of the patients had several complicating factors, but the main indications for performing the test are listed in Table I. The tests were performed on the antenatal ward along the lines outlined by Ray et a1 (1972). The patient was placed in the semirecumbent position and a Corometrics Fetal Monitor lOlB or 111 with external tocography and ultrasound was used to record the uterine activity and fetal heart. After a 15 to 20 minute baseline recording, intravenous oxytocin was infused until contractions were occurring every 3 to 4 minutes. The fetal heart was then assessed over ten contractions. The interpretation of the test was as follows: 1. A negative test showed normal baseline variability and no decelerations of the fetal heart. In addition those tests with either early or intermittent variable decelerations were classified as negative. 2. A positive test was characterized by repeated (three or more consecutive) late decelerations (Hon, 1967).
ITis a decade since Hammacher (1966) suggested assessing the response of the fetal heart to oxytocin-induced contractions in high risk antepartum patients. The rationale is that even mild uterine contractions might induce hypoxia and late deceleration of the fetal heart rate if there is critical reduction of placental function. A number of authors (Kubli et al, 1969; Spurrett, 1971; Ray et al, 1972; Ewing et al, 1974; Schifrin et al, 1975; Cooper et al, 1975) have studied the value of the oxytocin challenge test (OCT) as a guide to the timing and mode of delivery in high-risk pregnancies. Most of these have involved relatively small numbers of patients and the conclusions as to the value and meaning of a positive test have varied. The purpose of this paper is to review a threeyear experience with the OCT in antepartum fetal assessment. METHODS The patients selected were those whose clinical condition made them more likely to 39
40
BASKETT AND SANDY
TABLE I Indications for performing oxytocin challenge test
TABLE I1 Oxytocin challenge test-fetal heart patterns obtained in 537 tests
Per cent
Per cent
~~
Pre-eclampsia Small-for-dates Prolonged pregnancy (42 weeks +) Chronic hypertension Diabetes mellitus Gestational diabetes Bad obstetrical history Elderly primigravida Others
38.9 15.1 11.8 8.4 1.4 6.0 5.8
2.2 4.4
3. A suspicious test was defined as one in which any of the following patterns occurred: persistent baseline tachycardia (more than 160 beats/minute), bradycardia (less than 120 beats/minute) or reduced variability (less than 5 beats/minute): repeated (three or more consecutive) variable decelerations or intermittent late decelerations. If negative, the test was repeated at weekly intervals until delivery. If suspicious or positive, the test was repeated in 24 to 48 hours, unless delivery of the patient was undertaken. Where possible, the fetal heart was continuously monitored in labour and this was achieved in 82 per cent of patients. The result of the OCT was correlated with the following factors : intrapartum meconium staining, repeated late decelerations during the last hour of labour, the one and five minute Apgar scores, intrauterine growth retardation (less than 10th centile, Pusey and Haworth, 1969), the need for neonatal resuscitation (defined as intubation and beyond), the need for admission to the neonatal intensive care unit, and the stillbirth and neonatal death rates.
RESULTS There were 537 satisfactory tests performed on 364 patients over the three-year period 1973 to 1975. The number of tests performed on a patient ranged from one to eight. The type and frequency of fetal heart patterns obtained are shown in Table 11. Of all the patients, 299 (82.2 per cent) had only negative tests, 38 (10.4 per cent) had a suspicious test and 27 (7.4 per cent) had a positive test result.
Rate Normal Bradycardia Tachycardia Baseline variability Normal Reduced Decelerations Early Variable intermittent Variable repetitive Late intermittent Late repetitive (Positive test)
98.5 0.9 0.6 96.3 3.1 2.4 15.5 1.1 5.0 6.9
The correlation of the patients with the three different test results and the perinatal outcome is shown in Table Ill. It is obvious that those patients with a positive OCT had the worst perinatal outcome. When the patients with positive tests were compared to those with negative and suspicious results the differences were statistically significant (p
