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Amniotomy and the use of oxytocin in labor in nulliparous women
Amniotomy and the use of oxytocin in labor in nulliparous women Joseph Seitchik, M.D., Alan E. C. Holden, M.A., and Maria Castillo, R.N. San Antonio, Texas A group of242 nulliparous women in spontaneous, term, first-stage, true labor, with cephalic presentations and intact membranes, underwent amniotomy in the first stage. Sixty-nine of 242 (29%) received oxytocin prior to complete dilatation. The group that received oxytocin was characterized by fewer women less than 20 years of age, more patients with an additional diagnosis such as preeclampsia, longer labors, and slower mean rates of dilatation before and after amniotomy. There was no correlation between the last dilatation rate before and the first after amniotomy. The only significant predictors of oxytocin use were cervical dilatation at amniotomy and the first rate of dilatation afterward. Of patients with dilatation at a rate of ~1 cm/hr from admission to amniotomy, 16% received oxytocin; if <1 cm/hr, 39%. Two different rate standards were used to differentiate "unsatisfactory" from "satisfactory" labor: (1) <1 or ~1 cm/hr and (2) no change or some change in dilatation. Neither of these standards, when applied to the first examination after amniotomy, predicts patients who will receive oxytocin with any reasonable degree of efficiency. Examination of cervical dilatation after amniotomy in patients who did not receive oxytocin demonstrated failure of the cervix to dilate in approximately 20% of each of three sequential examinations. Contrariwise, no dilatation for 2 hours was uncommon. Amniotomy appears to enhance the dilatation rate in patients with well-dilated cervices that are already dilating at a satisfactory rate and slows dilatation in some patients, particularly those with cervices that are less dilated. These results suggest that amniotomy should be performed for specific indications only. (AM J OssTET GYNECOL 1985;153:848-54.)
Key words: Amniotomy, oxytocin use, nulliparous labor, vaginal delivery Measures used to assess the effects of amniotomy on established labor include the lengths of the first and second stages of labor, the rates of cervical dilatation in the latent and active phases of the first stage, the efficiency of the contractile force in the enhancement of the cervical dilatation rate, the frequency of variants from the usual heart rate patterns, and the prevalence of operative delivery.'· 7 The frequency of oxytocin administration after amniotomy has not been examined. The use of oxytocin in 40% of laboring nulliparous women by physicians who practice prompt amniotomy after labor suite admission suggests a possible relationship.8 In this study of a group of nulliparous women who were delivered vaginally, the clinical events before and after amniotomy are contrasted and examined in the light of the subsequent use of oxytocin.
Methods All study patients were delivered vaginally and were selected in the following manner. During the approximate year from April 1, 1983, to March 10, 1984, 300
From the Department of Obstetrics and Gynecology, The University of Texas Health Science Center at San Antonio. Received for publication August 23, 1985; accepted September 23, 1985. Reprint requests: Dr. Joseph Seitchik, Department of Obstetrics and Gynecology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78284.
848
Table I. Amniotomy study
No. of patients Age <20 yr (%) Diagnosis in addition to labor at admission(%) Received magnesium sulfate(%) Arrest in second stage (epidural excluded) (%) Duration of labor Admission to delivery > 12 hr (%) Mean± SD (hr) Cervical dilatation (em) (mean± SD) At admission At amniotomy Cervical dilatation rate (cm/hr) (mean± SD) Admission to amniotomy Last before amniotomy First after amniotomy
No oxytocin
Oxytocin
173 68 13
69 52* 38t
8
3lt
3
12*
23* I 5.1 ± 2.9 10.8 ± 3.9t 4.4 ± 1.3 6.4 ± 1.9
3.8 ± l.lt 4.8 ± l.St
1.2 ± 1.4 1.6 ± 1.9 2.8 ± 3.8
0.6 ± 0.6t 0.8 ± 0.9* 0.3 ± 0.8t
*p < 0.01. tp < 0.001.
consecutive cesarean sections were performed in nulliparous women with singleton fetuses. The last nulliparous woman who was delivered vaginally just prior to each cesarean section and the first who was delivered just afterward compose the patient group used for this study (N = 600). We eliminated the data derived from
Amniotomy and oxytocin use in nulliparous labor 849
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Table II. Cervical dilatation rate before and after amniotomy Total
Rate after amniotomy
Total
I
?.]
n
%
62 54
50 55
123 98
56 44
116
52
221
100
n
61 44
50 45
105
48
all patients with the following characteristics: inductions of labor, breech presentations, low birth weight, complete dilatation at admission, and no diagnosis of labor or an uncertain diagnosis of labor at entry to the labor-delivery suite. Of the original 600 vaginal delivery patients, 148 with those criteria were eliminated; of the remaining 452, 242 underwent amniotomy in the first stage of labor, 69 (29%) of whom received oxytocin during the first stage and 173 (71%) of whom did not. There were a few missing values for all the variables. However, as a "worst case," at least 221 of 242 patients provided data, and the groups that did and did not receive oxytocin were similarly affected. The Statistical Package for the Social Sciences was used for data analysis," and the statistical methods used included x2 , twotailed Student's t test, one-way analysis of variance, least-squares regression (Pearson's r), and discriminant analysis. Results
The patients who received oxytocin were different from those who did not in respect to several variables other than those that were manifestations of poor progress of labor (Table 1): a lower incidence of younger patients, associated diseases such as preeclampsia and diabetes, and treatment with magnesium sulfate, as well as less cervical dilatation at admission. The groups were similar in respect to mean birth weight and frequency of 5-minute Apgar scores <7, use of operative vaginal delivery for abnormal fetal heart rate, numbers oflabor room visits prior to admission, and percentages of patients less than 60 inches tall or weighing > 199 pounds. The duration of labor from admission to delivery was less than 12 hours in all but two of 173 patients who did not receive oxytocin but was significantly greater in those who did; in 23% (16 of 69) it exceeded 12 hours. The cervical dilatation rates were faster both before and after amniotomy in the patients who did not receive oxytocin, but the standard deviations, which are ? 100% of the mean, mark the large intragroup variation. On the average, amniotomy enhanced the rate of dilatation from 1.6 ± 1.9 to 2.8 ± 3.8 cm/hr in the patients not destined to receive oxytocin (p < 0.01) but slowed the dilatation rate in the patients who did
I
%
%
n
cmlhr
Table III. Oxytocin use and cervical dilatation rate from admission to amniotomy by class intervals of cervical dilatation at amniotomy Cervical dilatation at amniotomy (em)
<4 4-4.5 5-5.5 6-6.5 7-7.5 8-8.5 9-9.5
No. of patients
Received oxytocin (%)
31 31 55 42 35 17 29
55 48 35 26 14 6 3
Dilatation rate (cmlhr)
0.46 0.43 0.76 0.80 1.43 2.10 2.99
± ± ± ± ± ± ±
0.82 0.64 1.00 0.45 0.97 1.34 3.57
receive oxytocin from 0.8 ± 0.9 to 0.3 ± 0.8 cm/hr (p < 0.01). The impact of amniotomy on the dilatation rate just before and just after amniotomy was examined in two ways. First, the patients were divided into two groups, those with dilatation at a rate of ? 1 cm/hr and those with dilatation < 1 cm/hr before amniotomy, and the first rate after amniotomy was examined (Table II). The X2 analysis demonstrated that there was no significant change in rates from just before to just after amniotomy. Of the patients with dilatation of < 1 cm/hr, dilatation continued at the same rate; of those with dilatation ? 1 cm/hr, dilatation continued at the same rate in only 55% after amniotomy. Second, leastsquares regression analysis of these pairs of values, that is, the rates of cervical dilatation just before and just after amniotomy for each patient, provided a coefficient of correlation of 0 .16, confirming the absence of any relationship of clinical importance between the rate of dilatation just before and that just after artificial rupture of the membranes. What is the most important determinant of oxytocin use after amniotomy, cervical dilatation at amniotomy or other variables? Because oxytocin was administered to 39% of patients with a dilatation rate of 1 cm/hr at amniotomy but to only 16% of those with a dilatation rate of? 1 cm/hr, the dilatation rate prior to amniotomy appeared to be a significant variable in respect to its ability to predict the subsequent use of oxytocin. However, it was not. Cervical dilatation at amniotomy was the best predictor of oxytocin use (Table III). When
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Seitchik, Holden, and Castillo
December 15, 1985 Am J Obstet Gynecol
Table V. Prediction of oxytocin use by discriminant analysis
Table IV. Oxytocin use by first rate of cervical dilatation after amniotomy > 1 or < 1 cm/hr and by class intervals of cervical dilatation at amniotomy Dilatation rate (cm/hr)
Cervical dilatation at amniotomy (em)
No. of patients
<1 <1 <1 <1 2:1 2:1 2:1 2:1
<4 4.0-5.5 6.0-7.5 8.0-9.5 <4 4.0-5.5 6.0-7.5 8.0-9.5
20 40 31 13 6 38 44 29
Predicted group
Received oxytocin
(%) 70 60 48 15 17 13 2 0
the data were grouped by cervical dilatation at amniotomy and the means of the cervical dilatation rates from admission to amniotomy for each cervical dilatation group were treated as the dependent variable, one-way analysis of variance segmented the rare means into three homogeneous subgroups (p < 0.05): 4 to 6.5 em, 7 to 8.5 em, and 8 to 9 em. The fact that two of the subgroups overlapped was a product of the statistical method and was of no importance in the interpretation of the data. These results indicate that the rate of dilatation from admission to amniotomy is a poor predictor of oxytocin use, whereas cervical dilatation is important. For example, of patients with 4 em of dilatation, 55% will receive oxytocin, a use rate double that of patients with 6 to 6.5 em of dilatation (26% ), although the mean rates of dilatation from admission to amniotomy for each of the cervical dilatation groups were not significantly different. The magnitude of oxytocin use was related to the first rate of cervical dilatation noted after amniotomy (Table IV). If the first rate of dilatation was :;;, 1 cm/hr, only seven of 117 (6%) received oxytocin; if< 1 cm/hr, 55 of 104 (53%) received oxytocin. It is important to recognize that, within each subgroup of the two groups of patients segregated by the dilatation rate, cervical dilatation at amniotomy was an obvious determinant of the rate of oxytocin use. Discriminant analysis was used to quantitate the ability of several variables to predict oxytocin use (Table V). The only significant predictors were cervical dilatation at amniotomy and the first rate of dilatation after amniotomy. Insignificant variables tested were age, magnesium sulfate use, associated disease, cervical dilatation at admission, and rates of dilatation prior to amniotomy. The two significant variables were able to predict oxytocin use in 79% of the cases, but cervical dilatation was the most important, identifying 72% of the cases on its own. We assume that the physician's decision to use or not to use oxytocin is based on the observation of cervical dilatation over a specific period of time after amni-
No oxytocin Actual group
No. of cases
n
No oxytocin Oxytocin
159 62
112 13
I
Oxytocin
%
n
70 21
47 49
I
%
30 79
otomy and not upon the indication for amniotomy, be it to enhance what is deemed a satisfactory or unsatisfactory cervical dilatation rate or to place a scalp electrode. If this assumption is true, then examination of the cervical dilatation rates after amniotomy in the patients who received oxytocin should reveal a consistent definition of the indication for oxytocin augmentation of labor. Study of the dilatation rates of the patients who did not receive oxytocin should reflect our concept of the limits of satisfactory labor progress. The progress of labor in our patients who did not receive oxytocin was examined in respect to the elapsed time from amniotomy to complete dilatation, cervical dilatation at amniotomy, and the rate of dilatation from amniotomy to complete dilatation (n = 161). The data were treated in retrospective and prospective fashion (Table VI). Retrospective analysis was accomplished by segmenting the data into quintile subsets of the time from amniotomy to complete dilatation.'" Prospective analysis was accomplished by dividing the data according to the cervical dilatation at amniotomy. There was a significant negative relationship between the amount of cervical dilatation at amniotomy and the time required from amniotomy to accomplish complete dilatation. Regardless of whether the data were segmented retrospectively by quintile subsets of the time from amniotomy to complete dilatation or prospectively by the cervical dilatation at amniotomy, an identical coefficient of correlation was obtained, - 0.56. Contrariwise, the relationship of the rate of dilatation to cervical dilatation at amniotomy was wholly dependent on the method of analysis. If analyzed prospectively, by cervical dilatation at amniotomy, the mean rate of dilatation was similar statistically for the entire range of dilatations from 4 to 9.5 em (r = 0.02). The large standard deviations of the rate means indicate that within each cervical dilatation group, whether <4 or 9 to 9.5 em, some patients experience rapid dilatation after amniotomy and some do not. Retrospective examination by quintiles of the time from amniotomy to complete dilatation indicates that the greater the dilatation at amniotomy, the faster the rate of dilatation from amniotomy to complete dilatation (r = 0.71). For example, the patients whose mean cervical dilatation was 8.3 ± 1.2 em at amniotomy experienced dilatation af-
Amniotomy and oxytocin use in nulliparous labor 851
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n
No oxytocin 173 (100%)*
=
No. of patients with complete dilatation (cumulative) = 50 (30%)
Some n = 143 (83%) 0.8 ± 0.6
None n = 30 (17%) 0.8 ± 0.3t
First examination (n = 173)
I Second examination (n = 123)
Third examination (n = 77)
Some n = 25 (20%) 1.6 ± 0.6
None n = 5 (4%) 1.6 ± 0.3
None n = 2 (3%) 5.5 ± 0.4
Some n = 3 (4%) 2.3 ± 0.8
None n = 1 (1%) 3.1 ± 0.0
n
Some n = 18 (23%) 3.4 ± 0.7
None = 15 (12%) 1.9 ± 1.0
None n = 6 (8%) 2.5 ± 1.0
No. of patients with complete dilatation (cumulative) = 96 (55%)
Some n = 78 (63%) 1.7 ± 0.8
None Some n = 9 (12%) n = 9 (12%) 3.3 ± 1.2 2.9 ± 1.5
Some n = 29 (38%) 2.3 ± 0.9
No. of patients with complete dilatation (cumulative) = 132 (76%)
Fig. 1. Data derived from three sequential examinations for cervical dilatation rate segmented by patients with (some) and without (none) change in cervical dilatation.* = Number in that examination group and percentage of patients. t = Elapsed time (mean ± SD) from amniotomy to that examination.
Table VI. Impact of segmenting data either by times from amniotomy to complete dilatation or by class intervals of dilatation at amniotomy on relationship of dilatation at amniotomy to rate of dilatation from amniotomy to complete dilatation (patients who did not receive oxytocin only, n = 161) Retrospective analysis fry quintiles of elapsed time from amniotomy to complete dilatation
Elapsed time (hr)
0.1-0.7 0.8-1.4 1.5-2.3 2.3-3.7 3.8-8.3
C eroical dilatation at amniotomy (em)
8.3 6.8 6.1 5.7 5.1
± ± ± ± ±
1.2 1.6 1.6 1.5 1.8
Dilatation rate (cm/hr)
4.2 3.2 2.2 1.6 0.9
± ± ± ± ±
1.7 1.6 0.9 0.6 0.4
ter amniotomy at a rate of 4.2 ± I. 7 cm/hr, but those in whom cervical dilatation averaged 5.1 ± 1.8 em experienced dilatation at a rate of 0.9 ± 0.4 em/hr. This outcome is an illusion created by the treatment of the data. It should surprise no one that the patients who are identified by the retrospective selection process "to have run the race in the shortest time" are then found "to have run the shortest distance at the fastest pace." For the purpose of determining our definition of acceptable norms, we examined the first three sequential rates of cervical dilatation after amniotomy in patients who never received oxytocin (Fig. 1). For each sequential rate determination the question was asked, "Did this examination reveal any change from the one immediately before?" The patients were then divided into two groups by the cervical examination results: those with no change in dilatation and those with some increase. The number and percentage of patients and the mean elapsed time from amniotomy to examination
Prospective analysis by class interoals of dilatation at amniotomy C eroical dilatation at amniotomy (em)
<4 4.0-4.5 5.0-5.5 6.0-6.5 7.0-7.5 8.0-8.5 9.0-9.5
Elapsed time (hr)
4.1 ± 3.7 ± 3.1 ± 2.0 ± 1.9 ± 1.3 ± 1.1±
1.8 2.0 2.2 1.2 1.5 0.9 1.4
Dilatation rate (cmlhr)
2.1 2.2 2.4 2.8 2.5 2.2 2.3
± ± ± ± ± ± ±
1.0 1.5 1.4 1.8 1.6 1.6 2.1
were provided for each subgroup. Division of the patients by those with some change versus those with no change over time was consistent with observations indicating that cessation of cervical dilatation for 2 hours suggests the need for oxytocin therapy.'' The data demonstrate that at each examination similar proportions of the patients had made no progress: 30 of 173 ( 17%) at the first examination, 20 of 123 (16%) at the second, and 18 of 77 (23%) at the third. However, further search demonstrated that only five of 173 patients who received no oxytocin demonstrated one episode of arrest of cervical dilatation for 2 hours or more. Rapid progress was typical of this group; 50 of 173 (29%) had full dilatation by the first examination, 96 of 173 (55%) by the second, and 132 of 176 (76%) by the third examination, which occurred 2.6 ± 1.1 hours after amniotomy. Of the 13 cases of cessation of cervical dilatation for 2 or more hours in patients not receiving oxytocin, four occurred prior to amniotomy, four
852
Seitchik, Holden, and Castillo
December 15, 1985 Am J Obstet Gynecol
Table VII. Effect of amniotomy on changing rate of dilatation from "satisfactory" to "unsatisfactory" by two different definitions of "satisfactory" and "unsatisfactory" Dilatation rate before and after amniotomy
Cervical dilatation at amniotomy (em)
<4 4.0-4.5 5.0-5.5 6.0-6.5 7.0-7.5 8.0-8.5 9.0-9.5 Total
Satisfactory before amniotomy (>0 cmlhr) No. of patients
27 31 54 42 35 16 27 232 (100%)
n
17 17 42 32 31 15 26 180
I
Unsatisfactory after amniotomy (0 cmlhr)
%
63 55 78 76 89 94 96 78
spanned an interval from before to after amniotomy, and five cases occurred after amniotomy. If cessation of cervical dilatation for at least 2 hours is a required antecedent to oxytocin use, evidence of this phenomenon should have been found consistently in our patients who received oxytocin; however, it was not. In only 33 of 68 (48%) cases did cervical dilatation cease for 2 or more hours after amniotomy and prior to oxytocin therapy. If the period prior to amniotomy was included, then the maximum frequency of application of the rule was 40 of 68 (59%). If the rule was relaxed to a minimum delay in dilatation time of I.5 hours, 48 of 68 (7I%) would have met that criterion. For the remaining 20 patients, 10 manifested continuous but slow labor progress, and the remaining I 0 patients had periods of cessation of dilatation of less than I.5 hours prior to the initiation of oxytocin therapy. O'Driscoll and Stronge' 2 and Melmed and Evans'' have suggested that a rate of> 1 or < 1 cm/hr is a useful gauge for identifying patients with satisfactory and unsatisfactory dilatation rates. We contrasted the effect of using this 1 cm/hr standard with a definition of satisfactory as any rate in excess of zero (Table VII). The question is asked, "How do these two separate standards used to define satisfactory and unsatisfactory labor progress differ in their assessment of the frequency of satisfactory rates prior to amniotomy and vary in their valuation of how often these satisfactory rates become unsatisfactory?" The 1 cm/hr standard indicates that only 46% of the patients had satisfactory dilatation just prior to amniotomy and the rates became unsatisfactory in 45% of these patients immediately after amniotomy. The standard of any dilatation rate greater than zero identifies 78% of the patients to be in satisfactory labor prior to amniotomy, and only 36% were deemed unsatisfactory immediately after amniotomy. The definition of satisfactory labor progress by I em/
n
6 9 16 9 15 3 6 64
I
Satisfactory before amniotomy (?.] cm/hr)
%
n
35 53 38 28 48 20 23 36
7 9 15 17 25 13 20 106
I
Unsatisfactory after amniotomy (<1 cmlhr)
%
n
26 29 28 40 71 81 74 46
6 6 9 5 13 3 6 48
I
%
86 67 60 29 52 23 30 45
hr in patients with dilatation <6 em seems singularly inappropriate. That standard found only 3I of II2 (28%) patients with dilatation of 6 em to be in satisfactory labor prior to amniotomy. The data indicate that a definition of satisfactory dilatation by the standard of I cm/hr is too strict, for it indicates about half of these patients to be in unsatisfactory labor, even though more than 70% were delivered without the benefit of oxytocin. Further, in all of the patients who did not receive oxytocin, complete dilatation was achieved in less than 9 hours after amniotomy. Neither of these standards is efficient in distinguishing patients who will and will not receive oxytocin (Table VIII). We applied these standards to the first dilatation rate after amniotomy and examined the relationship of the definitions of unsatisfactory labor to the subsequent use of oxytocin. The standard of a zero rate for the identification of unsatisfactory progress would select only 63% of patients who receive oxytocin and is singularly poor for patients with <5 em of dilatation at amniotomy, providing a recognition rate of only 50%. The standard of I cm/hr is quite efficient for it identified the unsatisfactory labor progress of 90% of the patients destined to receive oxytocin. Unfortunately, application of that standard to the whole population would have resulted in the administration of oxytocin to 32% of patients in whom labor was quite efficient without its benefits.
Comment These results demonstrate that: (I) there is no relationship between the rates of dilatation just prior to and just after amniotomy; (2) in patients with dilatation at the rate of:;;, 1 cm/hr from admission to amniotomy, I6% will receive oxytocin after amniotomy; (3) the rate of use of oxytocin is determined in the main by the dilatation of the cervix at amniotomy; (4) for patients not receiving oxytocin, there is a significant negative
Amniotomy and oxytocin use in nulliparous labor 853
Volume 153 Number 8
Table VIII. Frequency of an initial "unsatisfactory:' dilatation rate after amniotomy by two different definitions of "unsatisfactory" and relationship of these interpretations to oxytocin use Patients not receiving oxytocin
Patients receiving oxytocin
Dilatation rate
Dilatation rate Cervical dilatation at amniotomy (em)
<4 4.0-4.5 5.0-5.5 6.0-6.5 7.0-7.5 8.0-8.5 9.0-9.5
Total
n
I
0.0 cm/hr
<1.0 cm/hr
0.0 cmlhr No. of patients
%
n
I
No. of patients
%
15 15 19 11 5 1 1
6 9 13 8 5 0 1
40 60 68 73 100 0 100
14 11 18 10 5 1 1
93 73 95 91 100 100 100
67 (100%)
42
63
60
90
relationship between the time from amniotomy to full dilatation and dilatation at amniotomy; (5) for those patients, the mean rate of cervical dilatation from amniotomy to complete dilatation bears no relationship to cervical dilatation at amniotomy; (6) neither the standard of> 1 or < 1 cm/hr or that of some or no dilatation at each cervical examination identifies the patients who will or will not receive oxytocin; (7) at each sequential examination after amniotomy, one of five patients who will not receive oxytocin will show no change in cervical dilatation; and (8) cessation of cervical dilatation for at least 2 hours is observed in only 3% of the labors of patients who do not receive oxytocin. The study demonstrateS that amniotomy enhances the rate of dilatation in patients not destined to receive oxytocin. This result is obtained most frequently in patients with cervices that are already well dilated, ~7 em, and dilating at an adequate rate, ~ 1 em/hr. Our data generate the ironic but realistic attitude that amniotomy works best to enhance the speed of labor when it is needed least. In patients with dilatation at the rate of 1 cm/hr from admission to amniotomy, 16% will eventually receive oxytocin. This result suggests that amniotomy can have a deleterious effect on labor progress. These observations signify that amniotomy should not be performed during labor without significant indications. The value of amniotomy cannot be judged apart from the goals of the system of care provided. For example, if all but the lowest risk patients must be provided with continuous fetal heart monitoring, then amniotomy becomes an integral part of the care, and the problems that amniotomy may cause, such as the need for oxytocin, can only be measured in any gains derived from monitoring. If minimizing or eliminating the use of analgesia requires a guarantee to the patients of a labor room experience of< 12 hours, 12 then amniotomy and oxytocin are frequent imperatives and the prob-
12 12 35 31 30 15 26 161 (100%)
I
<1.0 cmlhr
I
%
n
2 3 4 3 10 3 5
17 25 11 10 33 20 19
7 8 9 4 12 4 7
58 67 26 13 40 27 27
30
19
51
32
n
%
!ems occasioned by their use can be evaluated only in terms of gains to mother and fetus by the avoidance of medications for pain relief. The issue of the rate of dilatation in those patients not receiving oxytocin is not a trivial one, for the change in cervical dilatation in time will determine when oxytocin is used. When the data from patients not receiving oxytocin are examined prospectively, the mean rate of cervical dilatation from amniotomy to full dilatation is the same regardless of the dilatation at amniotomy. Within each group of patients with a specific narrow range of cervical dilatation, there will be a wide range of dilatation rates after amniotomy, although the mean dilatation rates will be similar for all cervical dilatation groups. This marked variation in dilatation rates from amniotomy to complete dilatation for patients who never receive oxytocin indicates that the indications for oxytocin after amniotomy should be based upon deviations from the "worst case" performance of this group. Oxytocin use should not be based upon arbitrary statistical deviations from the means of heterogeneous patient groups. For example, one standard is a rate of 1 cm/hr, yet, of the patients who never receive oxytocin, about 20% will show no change in dilatation at all at each sequential examination after amniotomy. On the other hand, <3% of the patients who do not receive oxytocin during labor ever demonstrate cessation of cervical dilatation for more than 2 hours. Because this event occurs so uncommonly in these patients, it would seem to be a reasonable standard to be applied before oxytocin is used. REFERENCES l. Bainbridge NM, Nixon WCW, Smyth CN. The effect of
rupture of the membranes upon length of labor. J Obstet Gynaecol Br Emp 1958;65:189. 2. Lindgren L. The effect of rupture of the membranes upon the mechanism oflabor. Acta Obstet Gynecol Scand 1959;38:211.
Seitchik, Holden, and Castillo
3. Friedman EA, Sachtleben MR. Amniotomy and the course of labor. Obstet Gynecol 1963;22:755. 4. Cibils LA, Hendricks CH. Normal labor. AM J 0BSTET GYNECOL 1965;91 :385. 5. Wetrich DW. Effect of amniotomy upon labor. A controlled study. Obstet Gynecol 1970;35:800. 6. Lards RK, Work BAJr, Witting WC. Amniotomy during the active phase oflabor. Obstet Gynecol 1972;39:702. 7. Motter WJ, Weiss PAM. The timing of amniotomy: its influence on mother and infant. Wien Klin Wochens<:hr 1984;96:446. 8. Clinical report for the year 1983. National Maternity Hospital, Dublin.
December 15, 1985 Am J Obstet Gynecol
9. Nie NH, ed. SPSS. Statistical package for the social sciences. 2nd ed. New York: McGraw-Hill, 1975. 10. Hendricks CH, Brenner WE, Kraus G. Normal cervical dilatation pattern in late pregnancy and labor. AM J Qs. STETGYNECOL 1970;106:1065. II. Studd J, Clegg DR, Sanders RP, Hughes AD. Identification of high risk labors by labor nomogram. Br Med J 1975;2:545. 12. O'Driscoll K, Stronge JM. The active management of labor. Clin Obstet Gynaecol 1975;2:3. 13. Melmed H, Evans MI. Predictive value of cervical dilatation rates. I. primipara labor. Obstet Gynecol 1976:47: 511.
A comparison of ritodrine, terbutaline, and magnesium sulfate for the suppression of preterm labor Marie H. Beall, M.D., Bruce W. Edgar, M.D., Richard H. Paul, M.D., Toni Smith-Wallace, L.V.N.
Los Angeles, California Ritodrine, terbutaline, and magnesium sulfate have all been used in the United States as tocolytic drugs. Studies have shown each of these drugs to be effective in suppressing preterm labor. The current study was undertaken in order to compare their relative safety and efficacy and to evaluate the effectiveness of a second drug when the first-used drug failed to stop contractions. No differences in efficacy could be demonstrated between the drugs; however, there was a marked difference in the incidence of maternal side effects. Because of an unacceptable level of side effects, we have stopped the use of terbutaline at our institution. (AM J 0BSTET GYNECOL 1985;153:854-9.)
Key words: Tocolysis, ritodrine, terbutaline, magnesium sulfate Prematurity, together with its complications, remains the most frequent preventable cause of neonatal loss. In an attempt to prevent the sequelae of premature delivery attention has logically centered on efforts to find safe and effective tocolytic drugs. The drugs most commonly used in this country for the suppression of preterm labor are the ()-sympathomimetic agents ritodrine and terbutaline and magnesium sulfate. Each of these agents has been found to be more effective than ethanol'·• or placebo,<·6 and results have been superior to those in a historical control group. 7·10 All three agents have been associated with the occurrence of severe side
From the Department of Obstetrics and Gynecology, University of Southern California School of Medicine and Women's Hospital, Los Angeles County/University of Southern California Medical Center. Presented at the Fifth Annual Meeting of the Society of Perinatal Obstetricians, January 31-February 2, 1985. Received for publication March 29, 1985; accepted September 18, 1985.
Reprint requests: Marie H. Beall, M.D., Department of Obstetrics and Gynecology, Women's Hospital, Room 5K40, 1240 North Mission Road, Los Angeles, CA 90033.
854
effects such as pulmonary edema or respiratory depression.7· 11 Preliminary reports also indicate that the use of concurrent two-agent therapy is associated with an even greater incidence of side effects.' 2 Some data exist, however, to suggest that sequential therapy may be less hazardous and more effective."· 14 The present study was designed to compare the effectiveness of these three agents in suppressing premature labor and their relative risks to mother and fetus.
Material and methods Patients enrolled in this study were admitted to the labor area of the Obstetric Service of Women's Hospital between March 1, 1983, and july 31, 1984, with a clinical diagnosis of preterm labor. Preterm labor was defined as persistent uterine contractions more frequent than one every 10 minutes after Y2 hour of bed rest and hydration or documented cervical change at a gestational age <36 weeks or fetal weight <2500 gm. Patients were excluded from the study if they had experienced rupture of the amniotic membranes or for any of a number of contraindications to tocolysis or to
Key words: Amniotomy, oxytocin use, nulliparous labor, vaginal delivery Measures used to assess the effects of amniotomy on established labor include the lengths of the first and second stages of labor, the rates of cervical dilatation in the latent and active phases of the first stage, the efficiency of the contractile force in the enhancement of the cervical dilatation rate, the frequency of variants from the usual heart rate patterns, and the prevalence of operative delivery.'· 7 The frequency of oxytocin administration after amniotomy has not been examined. The use of oxytocin in 40% of laboring nulliparous women by physicians who practice prompt amniotomy after labor suite admission suggests a possible relationship.8 In this study of a group of nulliparous women who were delivered vaginally, the clinical events before and after amniotomy are contrasted and examined in the light of the subsequent use of oxytocin.
Methods All study patients were delivered vaginally and were selected in the following manner. During the approximate year from April 1, 1983, to March 10, 1984, 300
From the Department of Obstetrics and Gynecology, The University of Texas Health Science Center at San Antonio. Received for publication August 23, 1985; accepted September 23, 1985. Reprint requests: Dr. Joseph Seitchik, Department of Obstetrics and Gynecology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78284.
848
Table I. Amniotomy study
No. of patients Age <20 yr (%) Diagnosis in addition to labor at admission(%) Received magnesium sulfate(%) Arrest in second stage (epidural excluded) (%) Duration of labor Admission to delivery > 12 hr (%) Mean± SD (hr) Cervical dilatation (em) (mean± SD) At admission At amniotomy Cervical dilatation rate (cm/hr) (mean± SD) Admission to amniotomy Last before amniotomy First after amniotomy
No oxytocin
Oxytocin
173 68 13
69 52* 38t
8
3lt
3
12*
23* I 5.1 ± 2.9 10.8 ± 3.9t 4.4 ± 1.3 6.4 ± 1.9
3.8 ± l.lt 4.8 ± l.St
1.2 ± 1.4 1.6 ± 1.9 2.8 ± 3.8
0.6 ± 0.6t 0.8 ± 0.9* 0.3 ± 0.8t
*p < 0.01. tp < 0.001.
consecutive cesarean sections were performed in nulliparous women with singleton fetuses. The last nulliparous woman who was delivered vaginally just prior to each cesarean section and the first who was delivered just afterward compose the patient group used for this study (N = 600). We eliminated the data derived from
Amniotomy and oxytocin use in nulliparous labor 849
Volume 153 Number 8
Table II. Cervical dilatation rate before and after amniotomy Total
Rate after amniotomy
Total
I
?.]
n
%
62 54
50 55
123 98
56 44
116
52
221
100
n
61 44
50 45
105
48
all patients with the following characteristics: inductions of labor, breech presentations, low birth weight, complete dilatation at admission, and no diagnosis of labor or an uncertain diagnosis of labor at entry to the labor-delivery suite. Of the original 600 vaginal delivery patients, 148 with those criteria were eliminated; of the remaining 452, 242 underwent amniotomy in the first stage of labor, 69 (29%) of whom received oxytocin during the first stage and 173 (71%) of whom did not. There were a few missing values for all the variables. However, as a "worst case," at least 221 of 242 patients provided data, and the groups that did and did not receive oxytocin were similarly affected. The Statistical Package for the Social Sciences was used for data analysis," and the statistical methods used included x2 , twotailed Student's t test, one-way analysis of variance, least-squares regression (Pearson's r), and discriminant analysis. Results
The patients who received oxytocin were different from those who did not in respect to several variables other than those that were manifestations of poor progress of labor (Table 1): a lower incidence of younger patients, associated diseases such as preeclampsia and diabetes, and treatment with magnesium sulfate, as well as less cervical dilatation at admission. The groups were similar in respect to mean birth weight and frequency of 5-minute Apgar scores <7, use of operative vaginal delivery for abnormal fetal heart rate, numbers oflabor room visits prior to admission, and percentages of patients less than 60 inches tall or weighing > 199 pounds. The duration of labor from admission to delivery was less than 12 hours in all but two of 173 patients who did not receive oxytocin but was significantly greater in those who did; in 23% (16 of 69) it exceeded 12 hours. The cervical dilatation rates were faster both before and after amniotomy in the patients who did not receive oxytocin, but the standard deviations, which are ? 100% of the mean, mark the large intragroup variation. On the average, amniotomy enhanced the rate of dilatation from 1.6 ± 1.9 to 2.8 ± 3.8 cm/hr in the patients not destined to receive oxytocin (p < 0.01) but slowed the dilatation rate in the patients who did
I
%
%
n
cmlhr
Table III. Oxytocin use and cervical dilatation rate from admission to amniotomy by class intervals of cervical dilatation at amniotomy Cervical dilatation at amniotomy (em)
<4 4-4.5 5-5.5 6-6.5 7-7.5 8-8.5 9-9.5
No. of patients
Received oxytocin (%)
31 31 55 42 35 17 29
55 48 35 26 14 6 3
Dilatation rate (cmlhr)
0.46 0.43 0.76 0.80 1.43 2.10 2.99
± ± ± ± ± ± ±
0.82 0.64 1.00 0.45 0.97 1.34 3.57
receive oxytocin from 0.8 ± 0.9 to 0.3 ± 0.8 cm/hr (p < 0.01). The impact of amniotomy on the dilatation rate just before and just after amniotomy was examined in two ways. First, the patients were divided into two groups, those with dilatation at a rate of ? 1 cm/hr and those with dilatation < 1 cm/hr before amniotomy, and the first rate after amniotomy was examined (Table II). The X2 analysis demonstrated that there was no significant change in rates from just before to just after amniotomy. Of the patients with dilatation of < 1 cm/hr, dilatation continued at the same rate; of those with dilatation ? 1 cm/hr, dilatation continued at the same rate in only 55% after amniotomy. Second, leastsquares regression analysis of these pairs of values, that is, the rates of cervical dilatation just before and just after amniotomy for each patient, provided a coefficient of correlation of 0 .16, confirming the absence of any relationship of clinical importance between the rate of dilatation just before and that just after artificial rupture of the membranes. What is the most important determinant of oxytocin use after amniotomy, cervical dilatation at amniotomy or other variables? Because oxytocin was administered to 39% of patients with a dilatation rate of 1 cm/hr at amniotomy but to only 16% of those with a dilatation rate of? 1 cm/hr, the dilatation rate prior to amniotomy appeared to be a significant variable in respect to its ability to predict the subsequent use of oxytocin. However, it was not. Cervical dilatation at amniotomy was the best predictor of oxytocin use (Table III). When
850
Seitchik, Holden, and Castillo
December 15, 1985 Am J Obstet Gynecol
Table V. Prediction of oxytocin use by discriminant analysis
Table IV. Oxytocin use by first rate of cervical dilatation after amniotomy > 1 or < 1 cm/hr and by class intervals of cervical dilatation at amniotomy Dilatation rate (cm/hr)
Cervical dilatation at amniotomy (em)
No. of patients
<1 <1 <1 <1 2:1 2:1 2:1 2:1
<4 4.0-5.5 6.0-7.5 8.0-9.5 <4 4.0-5.5 6.0-7.5 8.0-9.5
20 40 31 13 6 38 44 29
Predicted group
Received oxytocin
(%) 70 60 48 15 17 13 2 0
the data were grouped by cervical dilatation at amniotomy and the means of the cervical dilatation rates from admission to amniotomy for each cervical dilatation group were treated as the dependent variable, one-way analysis of variance segmented the rare means into three homogeneous subgroups (p < 0.05): 4 to 6.5 em, 7 to 8.5 em, and 8 to 9 em. The fact that two of the subgroups overlapped was a product of the statistical method and was of no importance in the interpretation of the data. These results indicate that the rate of dilatation from admission to amniotomy is a poor predictor of oxytocin use, whereas cervical dilatation is important. For example, of patients with 4 em of dilatation, 55% will receive oxytocin, a use rate double that of patients with 6 to 6.5 em of dilatation (26% ), although the mean rates of dilatation from admission to amniotomy for each of the cervical dilatation groups were not significantly different. The magnitude of oxytocin use was related to the first rate of cervical dilatation noted after amniotomy (Table IV). If the first rate of dilatation was :;;, 1 cm/hr, only seven of 117 (6%) received oxytocin; if< 1 cm/hr, 55 of 104 (53%) received oxytocin. It is important to recognize that, within each subgroup of the two groups of patients segregated by the dilatation rate, cervical dilatation at amniotomy was an obvious determinant of the rate of oxytocin use. Discriminant analysis was used to quantitate the ability of several variables to predict oxytocin use (Table V). The only significant predictors were cervical dilatation at amniotomy and the first rate of dilatation after amniotomy. Insignificant variables tested were age, magnesium sulfate use, associated disease, cervical dilatation at admission, and rates of dilatation prior to amniotomy. The two significant variables were able to predict oxytocin use in 79% of the cases, but cervical dilatation was the most important, identifying 72% of the cases on its own. We assume that the physician's decision to use or not to use oxytocin is based on the observation of cervical dilatation over a specific period of time after amni-
No oxytocin Actual group
No. of cases
n
No oxytocin Oxytocin
159 62
112 13
I
Oxytocin
%
n
70 21
47 49
I
%
30 79
otomy and not upon the indication for amniotomy, be it to enhance what is deemed a satisfactory or unsatisfactory cervical dilatation rate or to place a scalp electrode. If this assumption is true, then examination of the cervical dilatation rates after amniotomy in the patients who received oxytocin should reveal a consistent definition of the indication for oxytocin augmentation of labor. Study of the dilatation rates of the patients who did not receive oxytocin should reflect our concept of the limits of satisfactory labor progress. The progress of labor in our patients who did not receive oxytocin was examined in respect to the elapsed time from amniotomy to complete dilatation, cervical dilatation at amniotomy, and the rate of dilatation from amniotomy to complete dilatation (n = 161). The data were treated in retrospective and prospective fashion (Table VI). Retrospective analysis was accomplished by segmenting the data into quintile subsets of the time from amniotomy to complete dilatation.'" Prospective analysis was accomplished by dividing the data according to the cervical dilatation at amniotomy. There was a significant negative relationship between the amount of cervical dilatation at amniotomy and the time required from amniotomy to accomplish complete dilatation. Regardless of whether the data were segmented retrospectively by quintile subsets of the time from amniotomy to complete dilatation or prospectively by the cervical dilatation at amniotomy, an identical coefficient of correlation was obtained, - 0.56. Contrariwise, the relationship of the rate of dilatation to cervical dilatation at amniotomy was wholly dependent on the method of analysis. If analyzed prospectively, by cervical dilatation at amniotomy, the mean rate of dilatation was similar statistically for the entire range of dilatations from 4 to 9.5 em (r = 0.02). The large standard deviations of the rate means indicate that within each cervical dilatation group, whether <4 or 9 to 9.5 em, some patients experience rapid dilatation after amniotomy and some do not. Retrospective examination by quintiles of the time from amniotomy to complete dilatation indicates that the greater the dilatation at amniotomy, the faster the rate of dilatation from amniotomy to complete dilatation (r = 0.71). For example, the patients whose mean cervical dilatation was 8.3 ± 1.2 em at amniotomy experienced dilatation af-
Amniotomy and oxytocin use in nulliparous labor 851
Volume 153 Number 8
n
No oxytocin 173 (100%)*
=
No. of patients with complete dilatation (cumulative) = 50 (30%)
Some n = 143 (83%) 0.8 ± 0.6
None n = 30 (17%) 0.8 ± 0.3t
First examination (n = 173)
I Second examination (n = 123)
Third examination (n = 77)
Some n = 25 (20%) 1.6 ± 0.6
None n = 5 (4%) 1.6 ± 0.3
None n = 2 (3%) 5.5 ± 0.4
Some n = 3 (4%) 2.3 ± 0.8
None n = 1 (1%) 3.1 ± 0.0
n
Some n = 18 (23%) 3.4 ± 0.7
None = 15 (12%) 1.9 ± 1.0
None n = 6 (8%) 2.5 ± 1.0
No. of patients with complete dilatation (cumulative) = 96 (55%)
Some n = 78 (63%) 1.7 ± 0.8
None Some n = 9 (12%) n = 9 (12%) 3.3 ± 1.2 2.9 ± 1.5
Some n = 29 (38%) 2.3 ± 0.9
No. of patients with complete dilatation (cumulative) = 132 (76%)
Fig. 1. Data derived from three sequential examinations for cervical dilatation rate segmented by patients with (some) and without (none) change in cervical dilatation.* = Number in that examination group and percentage of patients. t = Elapsed time (mean ± SD) from amniotomy to that examination.
Table VI. Impact of segmenting data either by times from amniotomy to complete dilatation or by class intervals of dilatation at amniotomy on relationship of dilatation at amniotomy to rate of dilatation from amniotomy to complete dilatation (patients who did not receive oxytocin only, n = 161) Retrospective analysis fry quintiles of elapsed time from amniotomy to complete dilatation
Elapsed time (hr)
0.1-0.7 0.8-1.4 1.5-2.3 2.3-3.7 3.8-8.3
C eroical dilatation at amniotomy (em)
8.3 6.8 6.1 5.7 5.1
± ± ± ± ±
1.2 1.6 1.6 1.5 1.8
Dilatation rate (cm/hr)
4.2 3.2 2.2 1.6 0.9
± ± ± ± ±
1.7 1.6 0.9 0.6 0.4
ter amniotomy at a rate of 4.2 ± I. 7 cm/hr, but those in whom cervical dilatation averaged 5.1 ± 1.8 em experienced dilatation at a rate of 0.9 ± 0.4 em/hr. This outcome is an illusion created by the treatment of the data. It should surprise no one that the patients who are identified by the retrospective selection process "to have run the race in the shortest time" are then found "to have run the shortest distance at the fastest pace." For the purpose of determining our definition of acceptable norms, we examined the first three sequential rates of cervical dilatation after amniotomy in patients who never received oxytocin (Fig. 1). For each sequential rate determination the question was asked, "Did this examination reveal any change from the one immediately before?" The patients were then divided into two groups by the cervical examination results: those with no change in dilatation and those with some increase. The number and percentage of patients and the mean elapsed time from amniotomy to examination
Prospective analysis by class interoals of dilatation at amniotomy C eroical dilatation at amniotomy (em)
<4 4.0-4.5 5.0-5.5 6.0-6.5 7.0-7.5 8.0-8.5 9.0-9.5
Elapsed time (hr)
4.1 ± 3.7 ± 3.1 ± 2.0 ± 1.9 ± 1.3 ± 1.1±
1.8 2.0 2.2 1.2 1.5 0.9 1.4
Dilatation rate (cmlhr)
2.1 2.2 2.4 2.8 2.5 2.2 2.3
± ± ± ± ± ± ±
1.0 1.5 1.4 1.8 1.6 1.6 2.1
were provided for each subgroup. Division of the patients by those with some change versus those with no change over time was consistent with observations indicating that cessation of cervical dilatation for 2 hours suggests the need for oxytocin therapy.'' The data demonstrate that at each examination similar proportions of the patients had made no progress: 30 of 173 ( 17%) at the first examination, 20 of 123 (16%) at the second, and 18 of 77 (23%) at the third. However, further search demonstrated that only five of 173 patients who received no oxytocin demonstrated one episode of arrest of cervical dilatation for 2 hours or more. Rapid progress was typical of this group; 50 of 173 (29%) had full dilatation by the first examination, 96 of 173 (55%) by the second, and 132 of 176 (76%) by the third examination, which occurred 2.6 ± 1.1 hours after amniotomy. Of the 13 cases of cessation of cervical dilatation for 2 or more hours in patients not receiving oxytocin, four occurred prior to amniotomy, four
852
Seitchik, Holden, and Castillo
December 15, 1985 Am J Obstet Gynecol
Table VII. Effect of amniotomy on changing rate of dilatation from "satisfactory" to "unsatisfactory" by two different definitions of "satisfactory" and "unsatisfactory" Dilatation rate before and after amniotomy
Cervical dilatation at amniotomy (em)
<4 4.0-4.5 5.0-5.5 6.0-6.5 7.0-7.5 8.0-8.5 9.0-9.5 Total
Satisfactory before amniotomy (>0 cmlhr) No. of patients
27 31 54 42 35 16 27 232 (100%)
n
17 17 42 32 31 15 26 180
I
Unsatisfactory after amniotomy (0 cmlhr)
%
63 55 78 76 89 94 96 78
spanned an interval from before to after amniotomy, and five cases occurred after amniotomy. If cessation of cervical dilatation for at least 2 hours is a required antecedent to oxytocin use, evidence of this phenomenon should have been found consistently in our patients who received oxytocin; however, it was not. In only 33 of 68 (48%) cases did cervical dilatation cease for 2 or more hours after amniotomy and prior to oxytocin therapy. If the period prior to amniotomy was included, then the maximum frequency of application of the rule was 40 of 68 (59%). If the rule was relaxed to a minimum delay in dilatation time of I.5 hours, 48 of 68 (7I%) would have met that criterion. For the remaining 20 patients, 10 manifested continuous but slow labor progress, and the remaining I 0 patients had periods of cessation of dilatation of less than I.5 hours prior to the initiation of oxytocin therapy. O'Driscoll and Stronge' 2 and Melmed and Evans'' have suggested that a rate of> 1 or < 1 cm/hr is a useful gauge for identifying patients with satisfactory and unsatisfactory dilatation rates. We contrasted the effect of using this 1 cm/hr standard with a definition of satisfactory as any rate in excess of zero (Table VII). The question is asked, "How do these two separate standards used to define satisfactory and unsatisfactory labor progress differ in their assessment of the frequency of satisfactory rates prior to amniotomy and vary in their valuation of how often these satisfactory rates become unsatisfactory?" The 1 cm/hr standard indicates that only 46% of the patients had satisfactory dilatation just prior to amniotomy and the rates became unsatisfactory in 45% of these patients immediately after amniotomy. The standard of any dilatation rate greater than zero identifies 78% of the patients to be in satisfactory labor prior to amniotomy, and only 36% were deemed unsatisfactory immediately after amniotomy. The definition of satisfactory labor progress by I em/
n
6 9 16 9 15 3 6 64
I
Satisfactory before amniotomy (?.] cm/hr)
%
n
35 53 38 28 48 20 23 36
7 9 15 17 25 13 20 106
I
Unsatisfactory after amniotomy (<1 cmlhr)
%
n
26 29 28 40 71 81 74 46
6 6 9 5 13 3 6 48
I
%
86 67 60 29 52 23 30 45
hr in patients with dilatation <6 em seems singularly inappropriate. That standard found only 3I of II2 (28%) patients with dilatation of 6 em to be in satisfactory labor prior to amniotomy. The data indicate that a definition of satisfactory dilatation by the standard of I cm/hr is too strict, for it indicates about half of these patients to be in unsatisfactory labor, even though more than 70% were delivered without the benefit of oxytocin. Further, in all of the patients who did not receive oxytocin, complete dilatation was achieved in less than 9 hours after amniotomy. Neither of these standards is efficient in distinguishing patients who will and will not receive oxytocin (Table VIII). We applied these standards to the first dilatation rate after amniotomy and examined the relationship of the definitions of unsatisfactory labor to the subsequent use of oxytocin. The standard of a zero rate for the identification of unsatisfactory progress would select only 63% of patients who receive oxytocin and is singularly poor for patients with <5 em of dilatation at amniotomy, providing a recognition rate of only 50%. The standard of I cm/hr is quite efficient for it identified the unsatisfactory labor progress of 90% of the patients destined to receive oxytocin. Unfortunately, application of that standard to the whole population would have resulted in the administration of oxytocin to 32% of patients in whom labor was quite efficient without its benefits.
Comment These results demonstrate that: (I) there is no relationship between the rates of dilatation just prior to and just after amniotomy; (2) in patients with dilatation at the rate of:;;, 1 cm/hr from admission to amniotomy, I6% will receive oxytocin after amniotomy; (3) the rate of use of oxytocin is determined in the main by the dilatation of the cervix at amniotomy; (4) for patients not receiving oxytocin, there is a significant negative
Amniotomy and oxytocin use in nulliparous labor 853
Volume 153 Number 8
Table VIII. Frequency of an initial "unsatisfactory:' dilatation rate after amniotomy by two different definitions of "unsatisfactory" and relationship of these interpretations to oxytocin use Patients not receiving oxytocin
Patients receiving oxytocin
Dilatation rate
Dilatation rate Cervical dilatation at amniotomy (em)
<4 4.0-4.5 5.0-5.5 6.0-6.5 7.0-7.5 8.0-8.5 9.0-9.5
Total
n
I
0.0 cm/hr
<1.0 cm/hr
0.0 cmlhr No. of patients
%
n
I
No. of patients
%
15 15 19 11 5 1 1
6 9 13 8 5 0 1
40 60 68 73 100 0 100
14 11 18 10 5 1 1
93 73 95 91 100 100 100
67 (100%)
42
63
60
90
relationship between the time from amniotomy to full dilatation and dilatation at amniotomy; (5) for those patients, the mean rate of cervical dilatation from amniotomy to complete dilatation bears no relationship to cervical dilatation at amniotomy; (6) neither the standard of> 1 or < 1 cm/hr or that of some or no dilatation at each cervical examination identifies the patients who will or will not receive oxytocin; (7) at each sequential examination after amniotomy, one of five patients who will not receive oxytocin will show no change in cervical dilatation; and (8) cessation of cervical dilatation for at least 2 hours is observed in only 3% of the labors of patients who do not receive oxytocin. The study demonstrateS that amniotomy enhances the rate of dilatation in patients not destined to receive oxytocin. This result is obtained most frequently in patients with cervices that are already well dilated, ~7 em, and dilating at an adequate rate, ~ 1 em/hr. Our data generate the ironic but realistic attitude that amniotomy works best to enhance the speed of labor when it is needed least. In patients with dilatation at the rate of 1 cm/hr from admission to amniotomy, 16% will eventually receive oxytocin. This result suggests that amniotomy can have a deleterious effect on labor progress. These observations signify that amniotomy should not be performed during labor without significant indications. The value of amniotomy cannot be judged apart from the goals of the system of care provided. For example, if all but the lowest risk patients must be provided with continuous fetal heart monitoring, then amniotomy becomes an integral part of the care, and the problems that amniotomy may cause, such as the need for oxytocin, can only be measured in any gains derived from monitoring. If minimizing or eliminating the use of analgesia requires a guarantee to the patients of a labor room experience of< 12 hours, 12 then amniotomy and oxytocin are frequent imperatives and the prob-
12 12 35 31 30 15 26 161 (100%)
I
<1.0 cmlhr
I
%
n
2 3 4 3 10 3 5
17 25 11 10 33 20 19
7 8 9 4 12 4 7
58 67 26 13 40 27 27
30
19
51
32
n
%
!ems occasioned by their use can be evaluated only in terms of gains to mother and fetus by the avoidance of medications for pain relief. The issue of the rate of dilatation in those patients not receiving oxytocin is not a trivial one, for the change in cervical dilatation in time will determine when oxytocin is used. When the data from patients not receiving oxytocin are examined prospectively, the mean rate of cervical dilatation from amniotomy to full dilatation is the same regardless of the dilatation at amniotomy. Within each group of patients with a specific narrow range of cervical dilatation, there will be a wide range of dilatation rates after amniotomy, although the mean dilatation rates will be similar for all cervical dilatation groups. This marked variation in dilatation rates from amniotomy to complete dilatation for patients who never receive oxytocin indicates that the indications for oxytocin after amniotomy should be based upon deviations from the "worst case" performance of this group. Oxytocin use should not be based upon arbitrary statistical deviations from the means of heterogeneous patient groups. For example, one standard is a rate of 1 cm/hr, yet, of the patients who never receive oxytocin, about 20% will show no change in dilatation at all at each sequential examination after amniotomy. On the other hand, <3% of the patients who do not receive oxytocin during labor ever demonstrate cessation of cervical dilatation for more than 2 hours. Because this event occurs so uncommonly in these patients, it would seem to be a reasonable standard to be applied before oxytocin is used. REFERENCES l. Bainbridge NM, Nixon WCW, Smyth CN. The effect of
rupture of the membranes upon length of labor. J Obstet Gynaecol Br Emp 1958;65:189. 2. Lindgren L. The effect of rupture of the membranes upon the mechanism oflabor. Acta Obstet Gynecol Scand 1959;38:211.
Seitchik, Holden, and Castillo
3. Friedman EA, Sachtleben MR. Amniotomy and the course of labor. Obstet Gynecol 1963;22:755. 4. Cibils LA, Hendricks CH. Normal labor. AM J 0BSTET GYNECOL 1965;91 :385. 5. Wetrich DW. Effect of amniotomy upon labor. A controlled study. Obstet Gynecol 1970;35:800. 6. Lards RK, Work BAJr, Witting WC. Amniotomy during the active phase oflabor. Obstet Gynecol 1972;39:702. 7. Motter WJ, Weiss PAM. The timing of amniotomy: its influence on mother and infant. Wien Klin Wochens<:hr 1984;96:446. 8. Clinical report for the year 1983. National Maternity Hospital, Dublin.
December 15, 1985 Am J Obstet Gynecol
9. Nie NH, ed. SPSS. Statistical package for the social sciences. 2nd ed. New York: McGraw-Hill, 1975. 10. Hendricks CH, Brenner WE, Kraus G. Normal cervical dilatation pattern in late pregnancy and labor. AM J Qs. STETGYNECOL 1970;106:1065. II. Studd J, Clegg DR, Sanders RP, Hughes AD. Identification of high risk labors by labor nomogram. Br Med J 1975;2:545. 12. O'Driscoll K, Stronge JM. The active management of labor. Clin Obstet Gynaecol 1975;2:3. 13. Melmed H, Evans MI. Predictive value of cervical dilatation rates. I. primipara labor. Obstet Gynecol 1976:47: 511.
A comparison of ritodrine, terbutaline, and magnesium sulfate for the suppression of preterm labor Marie H. Beall, M.D., Bruce W. Edgar, M.D., Richard H. Paul, M.D., Toni Smith-Wallace, L.V.N.
Los Angeles, California Ritodrine, terbutaline, and magnesium sulfate have all been used in the United States as tocolytic drugs. Studies have shown each of these drugs to be effective in suppressing preterm labor. The current study was undertaken in order to compare their relative safety and efficacy and to evaluate the effectiveness of a second drug when the first-used drug failed to stop contractions. No differences in efficacy could be demonstrated between the drugs; however, there was a marked difference in the incidence of maternal side effects. Because of an unacceptable level of side effects, we have stopped the use of terbutaline at our institution. (AM J 0BSTET GYNECOL 1985;153:854-9.)
Key words: Tocolysis, ritodrine, terbutaline, magnesium sulfate Prematurity, together with its complications, remains the most frequent preventable cause of neonatal loss. In an attempt to prevent the sequelae of premature delivery attention has logically centered on efforts to find safe and effective tocolytic drugs. The drugs most commonly used in this country for the suppression of preterm labor are the ()-sympathomimetic agents ritodrine and terbutaline and magnesium sulfate. Each of these agents has been found to be more effective than ethanol'·• or placebo,<·6 and results have been superior to those in a historical control group. 7·10 All three agents have been associated with the occurrence of severe side
From the Department of Obstetrics and Gynecology, University of Southern California School of Medicine and Women's Hospital, Los Angeles County/University of Southern California Medical Center. Presented at the Fifth Annual Meeting of the Society of Perinatal Obstetricians, January 31-February 2, 1985. Received for publication March 29, 1985; accepted September 18, 1985.
Reprint requests: Marie H. Beall, M.D., Department of Obstetrics and Gynecology, Women's Hospital, Room 5K40, 1240 North Mission Road, Los Angeles, CA 90033.
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effects such as pulmonary edema or respiratory depression.7· 11 Preliminary reports also indicate that the use of concurrent two-agent therapy is associated with an even greater incidence of side effects.' 2 Some data exist, however, to suggest that sequential therapy may be less hazardous and more effective."· 14 The present study was designed to compare the effectiveness of these three agents in suppressing premature labor and their relative risks to mother and fetus.
Material and methods Patients enrolled in this study were admitted to the labor area of the Obstetric Service of Women's Hospital between March 1, 1983, and july 31, 1984, with a clinical diagnosis of preterm labor. Preterm labor was defined as persistent uterine contractions more frequent than one every 10 minutes after Y2 hour of bed rest and hydration or documented cervical change at a gestational age <36 weeks or fetal weight <2500 gm. Patients were excluded from the study if they had experienced rupture of the amniotic membranes or for any of a number of contraindications to tocolysis or to