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ORIGINAL RESEARCH |
From the Department of Obstetrics and Gynecology, University Hospital of Wales, Cardiff, United Kingdom.
Address reprint requests to: Andrew Sizer, MB, BCh, PhD Department of Obstetrics and Gynecology University Hospital of Wales Heath Park Cardiff South Glamorgan CF14 4XW United Kingdom E-mail: sizer{at}cardiff.ac.uk
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Abstract |
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Methods: A prospective observational study of 1413 women at term with a singleton, cephalic presentation. The position and station of the fetal head were observed and scored at diagnosis of the second stage of labor, 1 hour later, and then at 30 minute intervals until delivery was achieved. The score at diagnosis of the second stage of labor was assessed for its ability to predict eventual mode of delivery and duration of labor. A normogram was defined for nulliparas and multiparas and was used to define normal and abnormal progress in the second stage, associated factors in the first stage of labor, and mode of delivery.
Results: Increasing total score at the start of the second stage of labor is associated with increasing chance of spontaneous vaginal delivery (odds ratio [OR] 1.68 for nulliparas, 1.59 for multiparas), decreasing chance of instrumental vaginal delivery (OR 0.67 for nulliparas, 0.64 for multiparas), and emergency cesarean delivery (OR 0.39 for nulliparas). Abnormal progress as defined by the normogram is associated with use of epidural anesthesia, induction of labor, augmentation, dystocia, and increased incidence of operative delivery. No significant difference is found between normal and abnormal second stages of labor in fetal outcome as determined by Apgar scores.
Conclusion: The second-stage partogram offers an objective basis for management of the second stage of labor.
Graphic assessment of progress in labor was first suggested by Friedman.1–3 He proposed that of the major observable clinical factors in the first stage of labor, only cervical dilatation and descent of the presenting part were helpful in the assessment of progress, and he introduced the classic curves of mean dilatation1 and descent,3 plotted in a linear fashion, against time in labor. The establishment of a normal curve allowed various aberrations of dilatation and descent to be diagnosed and studied retrospectively.2,4
This approach was developed clinically as a composite partogram,5 with later modifications ( Studd JWW, Duignan N. Graphic records in labour [letter]. BMJ 1972;4:426).6 The latter version was based on a selected ideal population of nulliparous and multiparous women and included more information on the fetal and maternal condition. However, the original concept of assessing progress in labor graphically by serial examinations of cervical dilatation and descent of the presenting part was retained.
Experience in the use of the partogram showed that it clarified the recording and identification of abnormalities by comparison with an ideal profile of progress. It was time saving provided that the information was not duplicated, it facilitated teaching, and it allowed the use of normograms and improved recognition of abnormal patterns of dilatation and descent. Before introduction of the partogram, its validity was demonstrated by assessing the ability of a normogram to separate normal labors from those with an abnormal outcome.6
Once full dilatation is reached, the partogram stops and information is not graphically represented, thus losing the advantages outlined above. However, the need for a graphic display of progress into the second stage of labor may continue, especially when the second stage is prolonged, as increasingly occurs with use of epidural analgesia.7,8 Although descent continues, cervical dilation is no longer useful in the second stage, and additional variables are necessary to assess progress. The rate of descent of the presenting part, which may be ascertained by the station of the presenting part relative to the ischial spines, increases in the last part of the active phase of the first stage of labor. This increased rate of descent continues through the second stage of labor.2 Descent, which has been shown to be an important factor in assessing the progress of the first stage, may be proposed as a useful tool in the assessment of the second stage.
Descent in the second stage of labor is accompanied by rotation of the presenting part as it negotiates the pelvis. Friedman and Sachtleben4 showed that arrest of descent was frequently associated with fetal malpositions—occipitoposterior and occipitotransverse positions—and suggested that abnormalities of rotation were important prognostic factors in the second stage. Position is thus a second variable that may be used in observation of progress in the second stage.
The aims of our study were to introduce the concept of a second-stage partogram and to see whether it could be displayed easily and usefully in the clinical situation. The partogram was based on a scoring system of the variables of position and station; these variables and their combined score were assessed for their ability to predict eventual mode of delivery. A normogram line was constructed for the partogram on the basis of median scores at each time of assessment in the second stage, allowing classification of progress of the second stage as normal or abnormal. The development of the normogram line allowed comparison with time spent in the second stage of labor as an independent predictor of mode of delivery. Finally, the concept of normal and abnormal second stages was used to examine the effect of associated first-stage factors (use of epidural anesthesia, induction of labor, dystocia, prolonged 7–10 interval [interval between 7 cm of dilatation and full dilatation in the first stage of labor lasting longer than 3 hours9] and augmentation), mode of delivery, and fetal outcome.
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Materials and Methods |
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Details of the progress of the first stage of labor, including such complicating factors as administration of oxytocin for induction or augmentation, use of epidural block, presence or absence of first-stage dystocia (defined as progress of less than 1 cm of cervical dilatation per hour after 3 cm had been achieved), and a 7–10 interval longer than 3 hours,9 were noted.
Once established labor was diagnosed, vaginal examinations were routinely performed at 2-hour intervals throughout the first stage and were recorded on a standard partogram.6 The onset of the second stage of labor was diagnosed by vaginal examination or by the clinical finding of a visible vertex. The station and position of the head were recorded. Further vaginal assessment of station and position was performed after 1 hour and then, if possible and if the patient agreed to it, at 30-minute intervals until delivery. The time of delivery was recorded and the length of the second stage was calculated. The method of delivery and indications for any intervention were recorded. No women in the study underwent elective low forceps delivery for medical reasons, such as cardiac disease. No particular time limit was set for the second stage, but it seldom lasted more than 3 hours. Birth weight was noted. All vaginal examinations, recordings, and scoring were performed by the midwives and obstetric staff supervising the labor.
Information on station and position was scored as follows: occipitoanterior position was considered the most favorable and was scored 2; occipitotransverse positions were considered less favorable—they may be physiologic or may represent partial rotation of the fetal head to either occipitoanterior or occipitoposterior position—and were therefore scored 1. Occipitoposterior positions were deemed to be the least favorable and to represent malpresentation; these positions were scored zero.
Station was also scored. Station higher than 1 cm below the ischial spines was scored zero, station at spines + 1 was scored 1, and any station lower than this was scored 2. The maximum total score that could be obtained from position and station was 4. If the vertex was visible and anal dilatation was present, indicating exit from the bony pelvis and imminent delivery (equivalent to spines + 4), a score of 5 was awarded. Once delivery had occurred, a score of 6 was assigned, indicating the completion of the second stage of labor. A score was allocated after delivery so that the second-stage partogram could be completed graphically. The sum of descent and position scores was plotted against time elapsed in the second stage to give an indication of progress in each individual labor.
The relative importance of position, station, and total score was assessed for its ability to predict mode of delivery by using logistic regression.
A normogram was constructed for progress in the second stage by taking the median score at each time point of vaginal examination. Only scores less than 5 at the time of diagnosis of the second stage were used to construct the normogram. A normogram was constructed for both nulliparas and multiparas. Progress in the second stage was then categorized as normal or abnormal on the basis of the normogram. Second-stage labors that progressed on or to the left of the normogram line (Figure 1
) were classified as normal. Second-stage labors that had any point to the right of the normogram line were classified as abnormal.
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). However, total score improves the predictive range (the range of separation of incidence of a particular mode of delivery by highest and lowest scores) of mode of delivery to a greater expense than either position or station alone (Table 2, Figure 2). For example, at the time of commencement of the second stage of labor in nulliparas, a station score of 0 (the lowest score) predicts a spontaneous vaginal delivery rate of 36.7%, whereas a score of 2 (the highest score) predicts a spontaneous vaginal delivery rate of 62.3%. Compared with total score, the lowest and highest scores (0 and 5) predict spontaneous vaginal delivery rates of 25.0% and 96.9%, respectively. Total score therefore improves the predictive range.
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The scoring system that we devised was assessed statistically for its ability to predict mode of delivery. Table 2
shows that when total score is entered into univariate logistic regression, each incremental rise in score has a statistically significant effect on mode of delivery. When the components of position and station at start of the second stage are entered into multivariate logistic regression, each has an independent statistically significant effect on mode of delivery. Station is not a significant predictor of cesarean delivery in nulliparas, and station is not significantly associated with either spontaneous vaginal delivery or instrumental vaginal delivery in multiparas. Odds ratios (ORs) for position and station are similar in nulliparas, suggesting that an equal scoring system for these two variables is justified.
Median scores at 0, 60, and 90 minutes from the start of the second stage of labor were used to construct a normogram (Figure 1). Only data from women with a score less than 5 at the start of the second stage were used to construct the normogram because a score of 5 at these time points almost universally resulted in spontaneous vaginal delivery (Figure 1). The normogram was used to categorize second stages as normal or abnormal.
The ability of progress in the second stage according to the normogram to predict mode of delivery was compared with progress according to time spent in the second stage. For time spent in the second stage, the median value was obtained for nulliparas (67.5 minutes) and multiparas (14 minutes). Any second stage with a duration equal to or less than this median value was classified as normal; any second stage of longer duration was classified as abnormal. Table 3 shows the ability of normal and abnormal progress as defined by the partogram or by duration of the second stage to predict mode of delivery. The partogram is a better predictor of mode of delivery in both nulliparas and multiparas, although in multiparas the majority of women with an abnormal second stage still have a spontaneous vaginal delivery.
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demonstrates that use of epidural anesthesia, induction of labor, augmentation of labor with oxytocin, dystocia, and prolonged 7–10 interval are associated with a significantly reduced probability of a normal second stage of labor, as defined by the normogram that we constructed.
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. Infants born from a normal second stage are lighter than those from an abnormal second stage, although this difference is not statistically significant in multiparas. Apgar scores do not differ significantly between infants born from a normal second stage and those born from an abnormal second stage.
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Discussion |
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Many factors influence progress in the second stage: the size and shape of the pelvis, which may be related to the height of the mother; birth weight; uterine action; soft-tissue resistance; maternal effort; and degree of flexion, caput, and molding of the fetal head.2 However, these factors may all be resolved into the end result of descent and rotation, which allows simplified assessment and the possibility of graphic representation. The validity of this procedure is supported by the positive correlation found between the scores for position and station and positive outcome, ie, short duration of the second stage and spontaneous vaginal delivery. Our study also shows that a scoring system based on descent and rotation expressed graphically can chart second-stage progress in the second stage (Figure 1).
The distribution of the duration of the second stage reveals that although most of the nulliparas and multiparas in normal labor deliver quickly, a few of these women would benefit from a graphic display of their second stage. In women whose labors are complicated, the benefit of a partogram should be greater. The style of graphic representation described and the scoring system were readily accepted by the midwifery and medical staff. It was not found to be clinically intrusive, because 88% of women delivered within 1 hour and no further examination was required. Further assessments were needed after 1 hour in only 12% of women whose progress appeared to be slow; the extra clinical information was valuable in the management of these women. A degree of flexibility was allowed for in the half-hourly examinations, and omission of nonindicated vaginal examinations did not affect the partogram. The degree of observer agreement was not assessed statistically, but because definition of station and position is a normal midwifery skill, one could argue that a certain degree of observer error must be allowed for in the practical use of the partogram, in the same way that cervical dilatation is accepted in the first-stage partogram.
A scoring system based on position and station appears to differentiate between normal and abnormal labors and therefore satisfies the criteria under which the first-stage partogram was introduced.6 However, successful introduction of a second-stage partogram or scoring system depends on how it is to be used. The value of the second-stage partogram is limited. In the 88% of women who deliver by 1 hour, a visual display is unnecessary. Its value is more likely to be appreciated in women whose second stages continue beyond 1 hour and require clarification of the situation.
The initial score at the time of diagnosis of the second stage may be used as a predictor of the duration of the second stage and as a predictor of mode of delivery (Figure 2) and may be useful in the early identification of women at increased risk of difficult delivery.
A criticism could be made that the time of diagnosis of full dilatation varies among patients for various reasons, thus affecting the time scale. In our study, diagnosis of full dilatation was made by the midwife, as is normal in the labor ward, and the study results should therefore reflect progress in the second stage as it occurs in normal practice.
The effect of the introduction of second-stage partogram and interventions based on the scoring system must be evaluated in terms of clinical effectiveness, either in a clinical audit or a randomized controlled trial. The partogram must be assessed further for its acceptability to obstetric staff and patients with regard to clarification of recording, identification of abnormality, unnecessary vaginal examinations, and effect on operative delivery rates. The scoring system that may be used to predict problems either from the time of diagnosis of the second stage or after 1 hour must be assessed for its ability to improve outcome for the mother and infant without an unnecessary increase in medical intervention.
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Footnotes |
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Received January 24, 2000. Received in revised form May 1, 2000. Accepted May 18, 2000.
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References |
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2. Friedman EA. Labor: Clinical evaluation and management. 2nd edition. New York: Appleton Century Crofts, 1978.
3. Friedman EA, Sachtleben MR. Station of the presenting part. I. Pattern of descent. Am J Obstet Gynecol 1965;93:522–9.[Medline]
4. Friedman EA, Sachtleben MR. Station of the presenting part. IV. Arrest of descent in nulliparae. Obstet Gynecol 1976;47:129–36.
5. Philpott RH, Castle WM. Cervicographs in the management of labor in primigravidae. 1. The alert line for detecting abnormal labor. J Obstet Gynaecol Br Commonw 1972;79:592–8.[Medline]
6. Studd JWW. Partograms and normograms of cervical dilatation in the management of primigravid labor. BMJ 1973;4:451–5.
7. Kader N, Cruddas M, Campbell S. Estimating the probability of spontaneous delivery conditional on time spent in the second stage. Br J Obstet Gynaecol 1986;93:568–76.[Medline]
8. Paterson CM, Saunders NStG, Wadsworth J. The characteristics of the second stage of labor in 25,069 singleton deliveries in the North West Thames Health Region. Br J Obstet Gynaecol 1992;99:377–80.[Medline]
9. Davidson AC, Weaver JB, Davies P, Pearson J. The relation between ease of forceps delivery and speed of cervical dilatation. Br J Obstet Gynaecol 1976;83:279–83.[Medline]
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