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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Vaginal Birth After Cesarean
Sponsored by The Indian Health Service Clinical Support Center
6. Admission Scoring Systems
What are some of the factors that increase a successful VBAC?
A previous successful VBAC is probably the best predictor of future VBAC success. A prior vaginal delivery and, particularly, a prior VBAC are associated with a higher rate of successful trial of labor compared with patients with no prior vaginal delivery. Various studies have reported 90% or more of such women deliver vaginally with a trial of labor (TOL). Another study showed a history of a previous VBAC made it 7 times more likely to have a successful VBAC.
The higher rate of successful trial of labor was explained by lower rates of cesarean delivery for both fetal distress and labor dystocia. Identifying which women will be successful can help to decrease perinatal morbidity and mortality. Women who have had a previous successful VBAC, those who had a previous cesarean delivery for a nonrecurring indication, and those whose fetuses weighed less than 4,000 g at delivery are more likely to have successful VBAC attempts. Among women with one previous cesarean and one previous vaginal delivery, mothers whose most recent delivery was vaginal had a lower rate of cesarean delivery and shorter duration of labor than mothers whose most recent delivery was cesarean.
A Bishop score of 4 or more at the beginning of labor is a strong indicator for successful VBAC. Not unlike labor outside a VBAC setting, a favorable cervix increases the success rate for vaginal delivery 6-fold. An important point for any scoring system is that it should be applied at the time of admission, not at the last prenatal visit. Application before the onset of labor would not be valid. Cervical dilation and effacement often change dramatically between the last prenatal examination and the time of admission. No association has been found between the extent of dilation at the primary cesarean delivery and success of subsequent VBAC.
The vaginal delivery rate was significantly higher in patients with spontaneous labor compared with the induced labor. Care should be taken in the choice of induction agent. The use of prostaglandins for induction of labor in women with a previous cesarean delivery should be discouraged. Induction agents to consider in VBAC include oxytocin and mechanical methods. The safety of oxytocin for augmentation of contractions during a trial of labor after a previous low-transverse cesarean delivery has been examined in several studies. On average, 80 percent of women with spontaneous onset of labor delivered vaginally, versus 68 percent who received oxytocin.
Women delivered abdominally for dystocia are least successful at subsequent trial of labor after cesarean (TOLAC), although approximately two thirds are delivered vaginally. The success rate is higher if surgery was performed in the latent phase of labor and lower if performed after full dilation. If the prior cesarean delivery for dystocia was performed before complete cervical dilation (5-9 cm), 67-73% of VBAC attempts are successful compared with only 13% if the prior cesarean delivery was performed after complete cervical dilation. Most women who have undergone a cesarean delivery because of dystocia also can have a successful VBAC, but the percentage may be lower (50-80%) than for those with nonrecurring indications (75-86%). Although a patient with a history of cephalopelvic disproportion has the lowest success rate for vaginal birth after cesarean, an absolute cephalopelvic disproportion is almost never present. There is more than a 50% chance of success, which suggests that cephalopelvic disproportion should not be a limiting factor.
Patients aged 35 years or older compared with younger patients are more prone to have a failed TOL after a prior cesarean delivery. After adjusting for confounding variables, maternal age equal to or greater than 35 years was associated with a lower rate of successful vaginal delivery in patients without prior vaginal delivery.
Interdelivery intervals of up to 18 months were associated with increased risk of symptomatic uterine rupture during a trial of labor after cesarean delivery compared with that for longer interdelivery intervals.
Vaginal birth after cesarean delivery is not a contraindication to epidural anesthesia, and adequate pain relief may encourage more women to choose a trial of labor. Success rates for VBAC are similar in women who do and do not receive epidural analgesia, as well as in those women who receive other types of pain relief. Epidural analgesia rarely masks the signs and symptoms of uterine rupture.
Admission Scoring System
While investigating an admission scoring system Flamm and Geiger reported 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 trial of labor but has second thoughts about her mode of birth when labor begins. Other systems have also been proposed.
| Variable | Point Value |
|---|---|
| Age <40 years | 2 |
| Vaginal birth history | |
| Before and after 1st cesarean | 4 |
| After 1st cesarean | 2 |
| Before 1st cesarean | 1 |
| None | 0 |
| Reason other than failure to progress for 1st cesarean | 1 |
| Cervical effacement at admission (%) | |
| >75 | 2 |
| 25-75 | 1 |
| <25 | 0 |
| Cervical dilation > or = 4 at admission | 1 |
Data from Guise JM, McDonagh M, Hashima J, et al. Vaginal birth after cesarean (VBAC). Evidence Report/Technological Asessment No. 71. Rockville (MD): Agency for Healthcare Research and Quality; March 2003. p. 31 Table 2.
Five variables significantly 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. 82% of the patients had a score of 4 or higher and at least two thirds of these patients delivered vaginally. (See Flamm Scoring System Tool: Performance of Admission Score in the score testing group.)
| Score | # Subjects with score | % Subjects with V B A C |
|---|---|---|
| 0 - 2 | 114 | 49.1 |
| 3 | 329 | 59.9 |
| 4 | 595 | 66.7 |
| 5 | 660 | 77.0 |
| 6 | 360 | 88.6 |
| 7 | 189 | 92.6 |
| 8 - 10 | 158 | 94.9 |
| Total | 2405 | 74.9 |
Data from Guise JM, McDonagh M, Hashima J, et al. Vaginal birth after cesarean (VBAC). Evidence Report/Technological Asessment No. 71. Rockville (MD): Agency for Healthcare Research and Quality; March 2003. p. 32 Table 3.
