Predictive Value of the Admission VBAC Score
Predictive Value of the Admission VBAC Score
ABSTRACT & COMMENTARY
Synopsis: The admission VBAC scoring system may be useful when counseling patients about the likelihood of a successful TOL.
Source: Flamm BL, Geiger AM. Obstet Gynecol 1997;90:907-910.
To predict the likelihood of a vaginal birth after a cesarean delivery (VBAC), Flamm and Geiger developed a scoring system using factors known at the time of hospital admission for labor. The database for the study included 5022 patients from 10 hospitals in a large HMO system, all of whom had attempted a trial of labor (TOL). Half of the patients were randomly assigned to a score development group. Using multivariate logistic regression modeling, the investigators determined which variables to include in the VBAC scoring system. The most important predictive factors were patients younger than aged 40, history of a prior vaginal delivery, an indication other than failure to progress for the first cesarean delivery, and cervical effacement and dilation at admission. The admission scoring system was then applied to the other half of the patients in the database, who served as the score testing group. Possible scores ranged from 0 to 10, with a higher score being linearly associated with a greater likelihood of a successful TOL. Patients were awarded 2 points if they were less than 40 years of age; 4 points if they had had a vaginal delivery before and after their first cesarean; 2 points if the vaginal birth occurred after the first cesarean; 1 point if it had occurred before their cesarean birth; 0 points if they had not had a vaginal delivery; 1 point if their first cesarean delivery was performed for a reason other than failure to progress; 2 points if the cervix was more than 75% effaced at admission; 1 point for effacement of 25-75%; 0 points if less than 25% effaced; and 1 point if the cervix was dilated 4 cm or more at the time of admission. The data derived from the score testing group revealed the following association between the scoring system and the likelihood of a successful TOL: 0-2 points, 49.1%; 3 points, 59.9%; 4 points, 66.7%; 5 points, 77%; 6 points, 88.6%; 7 points, 92.6%; and 8-10 points, 94.9%.
Flamm and Geiger conclude that the admission VBAC scoring system may be useful when counseling patients about the likelihood of a successful TOL, particularly for those patients who are uncertain about their choices when labor begins.
COMMENT BY STEVEN G. GABBE, MD
Counseling patients who have had a prior, low transverse cesarean delivery about the likelihood of VBAC should begin early in pregnancy. The patient’s past medical history, including the records from her earlier labor(s) and operative notes, should be carefully examined. Patients often ask about their likelihood of having a successful TOL. They want to avoid a long labor ending unsuccessfully in a repeat cesarean delivery, which may be associated with greater morbidity. Previous studies have demonstrated that women who have had a prior vaginal delivery, who have had their cesarean section for reasons other than failure to progress, and who present in active labor are more likely to have a successful TOL. Flamm and Geiger analyzed their large database to develop a scoring system that can be used to counsel patients at the time of admission. Of note, the authors found that the number of prior cesarean deliveries, maternal weight gain, maternal one-hour glucose screening value, the diagnosis of gestational diabetes mellitus, and the status of membranes were not predictive of a successful or failed TOL. It is important to point out that women with a score of 0-2 had a 50% chance of a successful TOL, while approximately two-thirds of those with a score of 4 delivered vaginally. The authors emphasize that this scoring system was developed based on variables known at admission. However, we can advise our patients during their antenatal care that if they are younger than age 40, have had a prior vaginal delivery, and had a cesarean delivery for an indication other than for failure to progress, they have a good chance of a successful TOL. v
Based on the data of Flamm and Geiger, which of the following factors predicts a lower success rate for VBAC?
a. More than one prior cesarean delivery
b. Diagnosis of gestational diabetes mellitus
c. Prior cesarean delivery for placenta previa
d. Maternal weight gain of more than 30 pounds
e. Maternal age 40 years or older
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