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ORIGINAL RESEARCH |
From the Coastal Area Health Education Center, and New Hanover Regional Medical Center, Wilmington, North Carolina; and The School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Address reprint requests to: Sandra J. Diehl, MPH Coastal AHEC PO Box 9025 Wilmington, NC 28402-9025 E-mail: diehl{at}med.unc.edu
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Abstract |
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Methods: This prospective cohort study included 275 women in labor with live, singleton fetuses at term in vertex presentations. We excluded women with preeclampsia or previous cesarean deliveries. A multiple logistic regression model evaluated demographic and labor-related variables’ associations with cesarean risk.
Results: Fifty-nine of the 275 patients receiving epidural analgesia (21.5%) were delivered by cesarean, whereas 216 (78.5%) delivered vaginally. Variables that proved to be statistically significant in increasing the likelihood of cesarean were station at time of epidural placement (odds ratio [OR] 5.3; 95% confidence interval [CI] 2.6, 11.0; P < .001) and nulliparity (OR 3.8, 95% CI 1.8, 8.0; P < .001). Cervical dilation at the time of epidural placement was not a statistically significant predictor (OR 1.2, 95% CI 0.9, 1.6; P = .26). Cesareans were performed in 43 of 129 women (33.3%) who received epidurals with the vertex at a -1 station or higher, whereas only 16 of 146 women (11.0%) had cesareans if placement of the epidural was done after the vertex had reached at least a zero station.
Conclusion: Station at the time of epidural placement was more accurate predicting cesarean risk than cervical dilation. Placement of the epidural after the fetal vertex has become engaged in the pelvis (at least a zero station) resulted in a substantially lower cesarean risk.
Studies1–4 suggest that epidural anesthesia increases cesarean risk in laboring patients, and cervical dilation at the time of epidural placement is felt to be a strong predictor of dystocia risk. Some authors have suggested a significantly higher risk of cesarean delivery when the epidural is placed before 5 cm dilation,5,6 although one study1 found that slightly less than 80% of women still delivered vaginally under those conditions. Although it may be reasonable to infer that an epidural will not significantly increase the risk of dystocia and cesarean delivery if administered at or beyond 5 cm dilation, this requires a parturient to endure prolonged discomfort until she reaches that stage. This is unfortunate because epidural analgesia relieves labor pain effectively.7
Lack of normal rotation and descent of the fetal vertex secondary to relaxation of the pelvic musculature might cause epidural-associated dystocia.8 Thus, station at the time of epidural placement, rather than dilation, might be a more accurate predictor of dystocia and cesarean risk. This assertion was supported by a recent study9 showing an increased rate of malpresentation when epidural analgesia was placed with the fetal vertex at a high station, regardless of cervical dilation. Because timing of epidural placement involves balancing patient comfort with cesarean risk, knowing the best predictor is important for patient comfort and medical management. The purpose of this study was to compare station and cervical dilation, at the time of epidural placement, as predictors of cesarean delivery risk.
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Materials and Methods |
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Upon patient request, the managing physician determined the appropriateness and timing of the epidural. An anesthesiologist administered continuous, pump infusion, lumbar epidurals to women in labor, typically consisting of 3/16% bupivacaine and 2 µcgms/mL of fentanyl at 10–14 mL per hour.
A data collection form was placed in each patient’s admission anesthesia packet, and the private physician, resident physician, or labor and delivery nurse caring for the patient at the time of study enrollment was asked to complete it. At the time of epidural placement, providers recorded demographic and labor-related data, including maternal age, race, parity, years of education, and maternal height; gestational age and birth weight; oxytocin use before and after epidural; cervical examination at time of epidural placement, including dilation, effacement, and station; and indications for cesarean delivery. After delivery, providers recorded its type, vaginal or cesarean. Providers were oriented informally to the study and trained to complete the data collection form.
To determine if station of fetal vertex was a better predictor of a cesarean than cervical dilation, we constructed a multiple logistic regression model. The dichotomous dependent variable was cesarean delivery (yes versus no). The independent variables were station, coded as less than or equal to -1 and greater than or equal to zero, and cervical dilation (continuous). The control variables were parity (0 versus 1+), birth weight (continuous), height (continuous), and oxytocin use after epidural placement (yes versus no). Diagnostic tests were conducted on the logistic regression model, and there were no influential cases, specification errors, functional form errors, or problems with multicolinearity.
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Results |
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, are consistent with our overall obstetric population. Fifty-nine of 275 subjects (21.5%) who received an epidural were delivered ultimately by cesarean. Of those who delivered by cesarean, 13 (22%) were multiparous and 46 (78%) were nulliparous. Seventy-one of 275 patients (25.8%) had operative vaginal deliveries, whereas 145 of 275 patients (52.7%) delivered spontaneously. Indications given for cesarean showed that 48 of the 59 (81.3%) performed were for dystocia (failure to progress, cephalo-pelvic disproportion, or arrest of labor). The remaining cesarean deliveries were performed for nonreassuring fetal status (18.6%).
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summarizes delivery type per station at time of epidural placement. The data show that the cesarean rate was 33.3% (43 of 129) when the epidural was placed at a -1 station or higher, whereas it was 11.0% (16 of 146) when placed at a zero station or lower. Table 3 summarizes delivery type and cervical dilation at epidural placement; the cesarean rate was 25.8% (34 of 132) for women dilated at 4 cm or less, whereas it was 17.5% (25 of 143) for women dilated to 5 cm or more.
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). Women were five times more likely to have a cesarean if the epidural was placed at -1 station or higher than at zero station or lower.
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Discussion |
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In this prospective cohort study, dystocia and cesarean delivery were significantly more likely to occur if the epidural was placed with the fetal vertex still unengaged (at or above at -1 station). There was an associated fivefold increase in risk for cesarean delivery when these circumstances were compared with epidural placement, after the vertex had descended to at least a zero station. When stratified, nulliparous women also showed a fivefold risk, whereas multiparous women had a greater than fourfold risk. These results might indicate that once the fetal vertex has become engaged in the pelvis (the leading bony part of the skull at the level of the ischial spines or a zero station), epidural placement might create less risk for operative delivery.
The other variable found to be significant was nulliparity, carrying a greater than threefold increased risk of cesarean delivery. This was consistent with previous findings in the literature, suggesting that cesarean risk is greater for nulliparous females than for multiparous females.13 Cervical dilation at the time of epidural placement did not appear to affect cesarean risk among nulliparous women. Among multiparous women, dilation showed a weak association. This result differed from previous studies suggesting the value of cervical dilation in operative delivery risk assessment.5,6 Oxytocin use before and after epidural placement was not found to be significant.
One limitation of the study was the possibility of interobserver variation. In our study, 58 private and resident physicians and labor and delivery nurses collected cervical examination data. Because multiple providers recorded subjectively measured cervical examination data for this study, interpretations of measurements might vary. The data were obtained in a manner consistent with previous studies examining similar data. Standard practice on models and cervical boards, as well as performing actual examinations, is part of each provider’s training, and upper level residents and attending physicians check behind first- and second-year residents to help ensure accurate measurements.
Few empiric studies have examined interobserver variability related to cervical dilation and station measurement. However, those that have examined it found between 89.5 and 91.7% agreement (defined as either the same measurement, or within 1 cm of each other) when measuring cervical dilation on laboring women, or on simulated models.14–16 Exact agreement ranges from 42.0–56.3%. Studies reporting interobserver agreement on station are rare, but one study reported almost 90% agreement within 1 centimeter.14 Significant differences have not been found between types of practitioners (ie, private or resident physician, or labor and delivery nurse) or between varying years of professional experience.16
Another obvious limitation of our study was its observational design. Whether withholding epidural placement until zero station is reached actually reduces cesarean risk needs to be tested prospectively. It does appear that station at the time of epidural placement is a better predictor of cesarean risk than cervical dilation. The study also suggests that epidural placement before fetal vertex reaches zero station might increase operative delivery risk substantially. These findings provide the groundwork for future prospective investigation into improving patient comfort and assessing cesarean risk more accurately.
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Footnotes |
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Received April 13, 1998. Received in revised form July 24, 1998. Accepted August 6, 1998.
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References |
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2. Chestnut DH, McGrath JM, Vincent RD, Penning DH, Choi WW, Bates JN, et al. Does early administration of epidural analgesia affect obstetric outcome in nulliparous women who are in spontaneous labor? Anesthesiology 1994;80:1201–8.[Medline]
3. Lieberman E, Lang JM, Cohen A, D’Agostino R, Datta S, Frigoletto FD. Association of epidural analgesia with cesarean delivery in nulliparas. Obstet Gynecol 1996;88:993–1000.[Abstract]
4. Paterson CM, Saunders NS, Wadsworth J. The characteristics of the second stage of labour in 25,069 singleton deliveries in the North West Thames Health Region, 1988. Br J Obstet Gynaecol 1992;99:377–80.[Medline]
5. Thorp JA, Meyer BA, Cohen GR, Yeast JD, Hu D. Epidural analgesia in labor and cesarean delivery for dystocia. Obstet Gynecol Surv 1994;49:362–9.[Medline]
6. Thorp JA, Hu DH, Albin RM, McNitt J, Meyer BA, Cohen GR, et al. The effect of intrapartum epidural analgesia on nulliparous labor: A randomized, controlled, prospective trial. Am J Obstet Gynecol 1993;169:851–8.[Medline]
7. Ramin SM, Gambling DR, Lucas MJ, Sharma SK, Sidawi JE, Leveno KJ. Randomized trial of epidural versus intravenous analgesia during labor. Obstet Gynecol 1995;86:783–9.[Abstract]
8. Hoult IJ, MacLennan AH, Carrie LES. Lumbar epidural analgesia in labour: Relation to fetal malposition and instrumental delivery. BMJ 1977;1:14–6.
9. Robinson CA, Macones GA, Roth NW, Morgan MA. Does station of the fetal head at epidural placement affect the position of the fetal vertex at delivery? Am J Obstet Gynecol 1996;175:991–4.[Medline]
10. Goodfellow CF, Hull MGR, Swaab DF, Dogterom J, Buijs RM. Oxytocin deficiency at delivery with epidural analgesia. Br J Obstet Gynaecol 1983;90:214–9.[Medline]
11. Bates RG, Helm CW, Duncan A, Edmonds DK. Uterine activity in the second stage of labour and the effect of epidural analgesia. Br J Obstet Gynaecol 1985;92:1246–50.[Medline]
12. Thomas TA. Complications of epidural anaesthesia. In: Morgan B, ed. Problems in obstetric anaesthesia. New York: John Wiley and Sons, 1987:110.
13. Goyert GL, Bottoms SF, Treadwell MC, Nehra PC. The physician factor in cesarean birth rates. N Engl J Med 1989;320:706–9.[Abstract]
14. Bergsjo P, Koss KS. Interindividual variation in vaginal examination findings during labor. Acta Obstet Gynecol Scand 1982;61: 509–10.[Medline]
15. Tuffnell DJ, Bryce F, Johnson N, Lilford RJ. Simulation of cervical changes in labour: Reproducibility of expert assessment. Lancet 1989;2:1089–90.[Medline]
16. Phelps JY, Higby K, Smyth MH, Ward JA, Arredondo F, Mayer A. Accuracy and intraobserver variability of simulated cervical dilatation measurements. Am J Obstet Gynecol 1995;173:942–5.[Medline]
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