Slowing of active labor associated with internal fetal monitoring ROBERT
J.
SOKOL, M.D.
IVAN ZADOR, M.S. MORTIMER G. ROSEN, M.D.
Cleveland, Ohio
Active labor progress is generally believed to be linear. By using an ultrasonic cervimeter, which continuously records dilatation of the uterine cervix, awte decreases in active-phase dilatationfollowed by less rapid recoveries are found to be associated with intravaginal obstetric manipulations. These findings support the concepts that active labor may be nonlinear and regression in cervical dilatation is a real phenomenon.
periods, the reliability of our original observations could be questioned. However, with an instrument which continuously determines cervical dilatation with an accuracy of ±2 mm. from the transit time of ultrasound signals between piezoelectric crystals clipped at the three and nine o'clock positions on the uterine cervix, 2 it is possible to measure more accurately small changes in cervical dilatation, which may be associated with specific intrapartum events. It is our purpose in this communication to present an example of continuously recorded cervical dilatation from a labor during which the fetus was electronically and biochemically monitored and to comment on the associated nonlinearity of active labor.
PRoGRESS IN ACTIVE labor during the phase of maximum slope is generally thought of as being linear. This appears to be confirmed by examination of Friedman curves derived by averaging large numbers of labors. However, in 45 high-risk labors, evaluated in our initial studies of computer diagnosis of labor progression, 16 brief nonlinearities were identified during active labor. These were either short episodes of protracted active-phase dilatation, a low slope in active labor, or "shoulders," during which there was no change or a decrease (regression) in dilatation for less than two hours. Fifteen of these 16 were found to be temporally associated with simultaneous descent abnormality, amniotomy, narcotic analgesia, epidural anesthesia, or placement of internal monitors. 1 Because of these findings, we have used point-to-point labor diagnosis and evaluated the slope between each pair of successive vaginal examinations as a "finer" method of labor assessment than evaluation of smoothed curves. Since digital examination is intermittent, with reproducibility in the range of ±5 to lO per cent and cervical dilatation might not change very much over short
Case report A 20-year-old nullipara, with a benign antepartum course, entered the hospital at term in early latent labor with fingertip cervical dilatation and the vertex at -2 to -3 station. The labor pattern is shown graphically in Fig. 1. At 1226 hours (A), amniotomy was performed, and oxytocin stimulation and internal fetal monitoring were begun. At 1445 hours (B), after fetal bradycardia, a scalp microblood examination was performed (pH 7.40; base excess -4.9). At 1540 hours (D), it was necessary to reapply the scalp electrode. Labor then progressed smoothly, with spontaneous rotation of the occiput from posterior to anterior and without evidence of fetal distress. At 1856 hours, the patient was delivered spontaneously of a 3,560 gram female infant with Apgar scores of 9 and 10 at one and five minutes, respectively. Examination of the labor graph, based purely on clinical examinations (Fig. 1), shows that protracted active-phase dilatation (0.57 em. per hour) occurred
"From the Perinatal Clinical Research Center and the Department of Obstetrics and Gynecology, Cleveland Metropolitan General Hospital/Case Western Reserve University. Supported in part by United States Public Health Service Grants 5MOI-RR00210 and HD05566-0JAI and ir1 thR Cleveland Metropolitan General Hospital Foundation. Reprint requests: Dr. Robert]. Sokol, Co-director, Perinatal Clinical Research Center, Cleveland Metropolitan General Hospital, 3395 Scranton Rd., Clevewnd, Ohio 44109.
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Slowing of labor with internal monitoring 765
Volume 124 Number 7
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Fig. 1. Graph of a nulliparous labor (top) in occiput posterior position. x = Cervical dilatation; 0 station. Interval covered by segment of continuously recorded cervical dilatation tracing (bottom) is shown by solid line. The scale of the continuous record has been normalized so that clinical full dilatation equals exactly 10 em. At A, cervical dilatation was 4 to 5 em.; amniotomy was performed, and monitoring was begun. At B, a fetal scalp microblood examination was performed. At C, cervical dilatation was 6 em. At D, the scalp electrode was reapplied. At£, cervical dilatation was 7 em. Interval A to C toE represents protracted active-phase dilatation. IntervalE to F represents normal progress to full dilatation (see text).
from 1226 to 1650 hours (A to E, 4.5 to 7 em.). Point-to-point analysis shows that the slope from A to C was 0.58 em. per hour and that from C to E was 0.55 em. per hour. The continuous cervical dilatation record documents what actually happened. During the fetal scalp microblood examination (B), dilatation decreased acutely by 1 em. (slope = -20 em. per hour) and required 45 minutes to recover fully (slope = 2.4 em. per hour). Similarly, a little later, when the scalp electrode was reapplied (D), dilatation again decreased acutely and recovered more slowly.
Comment Point-to-point analysis of labor graphs based on digital vaginal examination suggests that active labor is not immune to slowing associated with obstetric interventions. These interventions might include, for example, amniotomy, analgesia, conduction anesthesia, and intravaginal fetal monitoring manipulations. The continuous cervical dilatation record supports the concepts that progress in active labor may be nonlinear and that regression in cervical dilatation is a real phenomenon; it cannot always be dismissed as resulting from inconsistent vaginal examination. In this case, the long-term picture of protracted activephase dilatation was produced when cervical dilatation
decreased acutely and recovered more slowly with a fetal scalp microblood determination and again with reapplication of the scalp electrode. Also, in this labor, the dilatation abnormality was associated with an apparent delay in descent. This and several other similarly mbnitored cases suggest that such short-term decreases in cervical dilatation may be related to loss of good application of the fetal presenting part to the cervix, as when the vertex is pushed up in the process of fetal scalp microblood sampling. Finally, our past experience suggests that delays in the active phase are more likely to occur in labors complicated by malposition, as in this case, or by disproportion. Here, analgesia and conduction anesthesia were avoided, and normal dilatation and spontaneous delivery occurred. Since it appears that factors adversely affecting labor progress tend to be cumulative, inappropriate interventions might have resulted in true secondary arrest of dilatation. We would speculate that when internal fetal monitoring is clinically indicated, other interventions, such as simultaneous analgesia or conduction anesthesia, should be avoided. Further investigation of active-phase slowing is warranted.
REFERENCES 1. Sokol, R. ].. Nussbaum, R. ]., Chik, L., and Rosen, M.G.:
Computer diagnosis of labor progression. 11. Application of an on-line interactive program in 45 high-risk labors, J. Reprod. Med. 11: 154, 1973. 2. Zador, 1., Wolfson, R.N., and Newman, M. R.: Ultrasonic
Measurement of Cervical Dilatation During Labor, Proceedings of the Twenty-seventh Annual Conference on Engineering in Medicine and Biology, Philadelphia, 1974, vol. 16, The Alliance for Engineering in Medicine and Biology, p. 187.
J.
SOKOL, M.D.
IVAN ZADOR, M.S. MORTIMER G. ROSEN, M.D.
Cleveland, Ohio
Active labor progress is generally believed to be linear. By using an ultrasonic cervimeter, which continuously records dilatation of the uterine cervix, awte decreases in active-phase dilatationfollowed by less rapid recoveries are found to be associated with intravaginal obstetric manipulations. These findings support the concepts that active labor may be nonlinear and regression in cervical dilatation is a real phenomenon.
periods, the reliability of our original observations could be questioned. However, with an instrument which continuously determines cervical dilatation with an accuracy of ±2 mm. from the transit time of ultrasound signals between piezoelectric crystals clipped at the three and nine o'clock positions on the uterine cervix, 2 it is possible to measure more accurately small changes in cervical dilatation, which may be associated with specific intrapartum events. It is our purpose in this communication to present an example of continuously recorded cervical dilatation from a labor during which the fetus was electronically and biochemically monitored and to comment on the associated nonlinearity of active labor.
PRoGRESS IN ACTIVE labor during the phase of maximum slope is generally thought of as being linear. This appears to be confirmed by examination of Friedman curves derived by averaging large numbers of labors. However, in 45 high-risk labors, evaluated in our initial studies of computer diagnosis of labor progression, 16 brief nonlinearities were identified during active labor. These were either short episodes of protracted active-phase dilatation, a low slope in active labor, or "shoulders," during which there was no change or a decrease (regression) in dilatation for less than two hours. Fifteen of these 16 were found to be temporally associated with simultaneous descent abnormality, amniotomy, narcotic analgesia, epidural anesthesia, or placement of internal monitors. 1 Because of these findings, we have used point-to-point labor diagnosis and evaluated the slope between each pair of successive vaginal examinations as a "finer" method of labor assessment than evaluation of smoothed curves. Since digital examination is intermittent, with reproducibility in the range of ±5 to lO per cent and cervical dilatation might not change very much over short
Case report A 20-year-old nullipara, with a benign antepartum course, entered the hospital at term in early latent labor with fingertip cervical dilatation and the vertex at -2 to -3 station. The labor pattern is shown graphically in Fig. 1. At 1226 hours (A), amniotomy was performed, and oxytocin stimulation and internal fetal monitoring were begun. At 1445 hours (B), after fetal bradycardia, a scalp microblood examination was performed (pH 7.40; base excess -4.9). At 1540 hours (D), it was necessary to reapply the scalp electrode. Labor then progressed smoothly, with spontaneous rotation of the occiput from posterior to anterior and without evidence of fetal distress. At 1856 hours, the patient was delivered spontaneously of a 3,560 gram female infant with Apgar scores of 9 and 10 at one and five minutes, respectively. Examination of the labor graph, based purely on clinical examinations (Fig. 1), shows that protracted active-phase dilatation (0.57 em. per hour) occurred
"From the Perinatal Clinical Research Center and the Department of Obstetrics and Gynecology, Cleveland Metropolitan General Hospital/Case Western Reserve University. Supported in part by United States Public Health Service Grants 5MOI-RR00210 and HD05566-0JAI and ir1 thR Cleveland Metropolitan General Hospital Foundation. Reprint requests: Dr. Robert]. Sokol, Co-director, Perinatal Clinical Research Center, Cleveland Metropolitan General Hospital, 3395 Scranton Rd., Clevewnd, Ohio 44109.
764
Slowing of labor with internal monitoring 765
Volume 124 Number 7
~·...
10
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0
~
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z
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i=
;!
A
5
05 F
l
0 € 0
2
X
1220
I
1300
I
1400
I
I
I
14415 1!500
I
1540 1600
I
I
1700
1737
TIME (hrsl
Fig. 1. Graph of a nulliparous labor (top) in occiput posterior position. x = Cervical dilatation; 0 station. Interval covered by segment of continuously recorded cervical dilatation tracing (bottom) is shown by solid line. The scale of the continuous record has been normalized so that clinical full dilatation equals exactly 10 em. At A, cervical dilatation was 4 to 5 em.; amniotomy was performed, and monitoring was begun. At B, a fetal scalp microblood examination was performed. At C, cervical dilatation was 6 em. At D, the scalp electrode was reapplied. At£, cervical dilatation was 7 em. Interval A to C toE represents protracted active-phase dilatation. IntervalE to F represents normal progress to full dilatation (see text).
from 1226 to 1650 hours (A to E, 4.5 to 7 em.). Point-to-point analysis shows that the slope from A to C was 0.58 em. per hour and that from C to E was 0.55 em. per hour. The continuous cervical dilatation record documents what actually happened. During the fetal scalp microblood examination (B), dilatation decreased acutely by 1 em. (slope = -20 em. per hour) and required 45 minutes to recover fully (slope = 2.4 em. per hour). Similarly, a little later, when the scalp electrode was reapplied (D), dilatation again decreased acutely and recovered more slowly.
Comment Point-to-point analysis of labor graphs based on digital vaginal examination suggests that active labor is not immune to slowing associated with obstetric interventions. These interventions might include, for example, amniotomy, analgesia, conduction anesthesia, and intravaginal fetal monitoring manipulations. The continuous cervical dilatation record supports the concepts that progress in active labor may be nonlinear and that regression in cervical dilatation is a real phenomenon; it cannot always be dismissed as resulting from inconsistent vaginal examination. In this case, the long-term picture of protracted activephase dilatation was produced when cervical dilatation
decreased acutely and recovered more slowly with a fetal scalp microblood determination and again with reapplication of the scalp electrode. Also, in this labor, the dilatation abnormality was associated with an apparent delay in descent. This and several other similarly mbnitored cases suggest that such short-term decreases in cervical dilatation may be related to loss of good application of the fetal presenting part to the cervix, as when the vertex is pushed up in the process of fetal scalp microblood sampling. Finally, our past experience suggests that delays in the active phase are more likely to occur in labors complicated by malposition, as in this case, or by disproportion. Here, analgesia and conduction anesthesia were avoided, and normal dilatation and spontaneous delivery occurred. Since it appears that factors adversely affecting labor progress tend to be cumulative, inappropriate interventions might have resulted in true secondary arrest of dilatation. We would speculate that when internal fetal monitoring is clinically indicated, other interventions, such as simultaneous analgesia or conduction anesthesia, should be avoided. Further investigation of active-phase slowing is warranted.
REFERENCES 1. Sokol, R. ].. Nussbaum, R. ]., Chik, L., and Rosen, M.G.:
Computer diagnosis of labor progression. 11. Application of an on-line interactive program in 45 high-risk labors, J. Reprod. Med. 11: 154, 1973. 2. Zador, 1., Wolfson, R.N., and Newman, M. R.: Ultrasonic
Measurement of Cervical Dilatation During Labor, Proceedings of the Twenty-seventh Annual Conference on Engineering in Medicine and Biology, Philadelphia, 1974, vol. 16, The Alliance for Engineering in Medicine and Biology, p. 187.
