Commentary and Review by:
Geffrey H. Klein, MD
OBGYN.net Advisory Board Chairman
Title: Vaginal Birth after Cesarean Delivery: An Admission Scoring System
Reference: Obstet Gynecol 1997;90:907-10
Authors: Bruce L. Flamm, MD <bruce.flamm@kp.org> and Ann M. Geiger, PhD
Institution: Kaiser Permanente Medical Centers, Southern California Region, Riverside, California
Study Design: Observational
Rating:Abstract:
Objective: To develop a scoring system to predict the likelihood of vaginal birth in patients undergoing a trial of labor after previous cesarean delivery using factors known at the time of hospital admission.
Methods: Trial of labor was attempted in 5022 patients who were assigned randomly to score derivation and score testing groups. Multivariate logistic regression modeling was used in the score derivation group to develop a predictive scoring system for vaginal birth. The scoring system was then applied to the testing group to evaluate its predictive ability.
Results: Five variables signifiacntly affected the mode of birth and were incorporated into a weighted scoring system. Rates of successful vaginal birth after cesarean ranged from 49% in patients scoring 0-2 to 95% in patients scoring 8-10. Increasing score was associated linearly with increasing probability of vaginal birth after cesarean.
Conclusion: Increasing scores correlate with increasing probability of vaginal birth after cesarean. The admission vaginal birth after cesarean scoring system may be useful in counseling patients regarding the option of vaginal birth or repeat cesarean delivery. This information could be particularly valuable for the patient who opts for a trial of labor but has second thoughts about her mode of birth when labor begins.
Commentary:
Trial of labor for vaginal birth after cesarean section is a proven standard of care practice. This is based on studies that demonstrated that the rate of successful vaginal delivery ranges from sixty to eighty percent. The enthusiasm for this approach is somewhat tempered by the potential for catastrophic uterine rupture and, to a lesser extent, the increased morbidity of a cesarean done for a failed trial of labor versus an elective repeat cesarean. In the ideal scenario, clinical factors could be used to distinguish which patients will deliver vaginally and which will not. This data would be invaluable in counseling patients regarding their options.
Flamm and Geiger have utilized the Kaiser-Permanente database to determine factors associated with a successful vaginal birth after cesarean. They developed a scoring system based on those factors to determine the likelihood of a successful trial of labor. This database was collected prospectively for two years and enrolled just over seven-thousand patients with a prior cesarean section. Of these, approximately five-thousand patients opted for trial of labor and were analyzed. The study randomly assigned half of these patients to the score development group and the other half to the score testing group. Data from the database included information on the patient's history, intrapartum course, and perinatal period. Those factors in each subgroup were analyzed for significance in determining outcome (p<0.05). Those found to be significant were analyzed in logistic regression for each sub-category of data and then for the data as a whole. This eliminated factors that would interact and confound the results. The final logistic regression model was used to place a weighted score for each factor of significance. The scoring system developed had a maximum score of ten and a minimum score of zero. To determine its validitity, the performance of the score was tested on the remaining half of the study population.
The randomization of the patients resulted in two similar groups. The overall vaginal delivery rate for the patients in both groups was seventy-four percent. Factors determined to be associated with vaginal birth in a trial of labor included age under forty, prior history of vaginal birth, indication other than failure to progress for first cesarean, cervical effacement greater than 75% on admission, and cervical dilation four centimeters or greater on admission. A summary of the weighted scoring system follows:
1 Age under 40 2 points 2 Prior vaginal birth: before and after cesarean 4 points after first cesarean 2 points before first cesarean 1 point none 0 points 3 Reason for first cesarean other than FTP 1 point 4 Admit effacement: >75% 2 points 25-75% 1 point < 25% 0 points 5 Admit dilation 4 cm or more 1 point In the score testing group, a score of 0-2 was associated with a 49% chance of vaginal delivery, whereas, a score of 8-10 was associated with a 95% chance of vaginal delivery.
The authors concluded that the scoring system has utility in counseling a patient in labor who has become unsure of her commitment to proceed. In a patient with a fifty percent chance of delivering vaginally, the information may sway her to repeat cesarean. Alternatively, if she is given a greater than ninety percent chance of delivering vaginally, she may encouraged to continue her trial of labor.
This study is interesting in its design. It is hard to determine how to classify a prospectively collected set of datapoints that is then examined retrospectively in a randomized fashion. However, the approach appears valid to this reviewer. The significance of the conclusions, does leave much to be desired. An ideal scoring system would result in low scores for those destined to fail a trial of labor and high scores for those likely to succeed. This is not the case. Those patients with low scores had a fifty percent chance of delivering, likely due to the fact that they are a heterogenous group. Within this group are the fifty percent almost certainly destined to have higher scores next time they are in labor. The reliance on prior delivery prevents any woman in her second pregnancy from scoring higher than six. Of the five-thousand patients in the study, only two hundred thirty, around five percent, would have achieved a score so low as to result in a "dismal" fifty percent chance of delivering vaginally. It would be interesting to study those women and query if they felt that a fifty percent chance of delivering would dissuade them from their chosen course. The ideal scoring system would also be able to be calculated prior to labor. If we could score patients in the late second and early third trimester the issue of trial of labor could be decided in the most appropriate place, the office. Unfortunately, this probably will never come to fruition. The fact that four of the five criteria for the scoring system are related to prior and current labor is logical. Even the most junior obstetrician knows that the chance of delivery is an almost certainty for the multipara in labor with a high bishop score.
