Keywords vaginal birth after cesarean - trial of labor after cesarean - MFMU VBAC calculator
- VBAC success
The decision between a trial of labor after cesarean (TOLAC) or an elective repeat
cesarean delivery (ERCD) can be difficult. A successful vaginal birth after cesarean
delivery (VBAC) is associated with lower maternal mortality, a shorter postpartum
recovery time, and a decreased risk of future pregnancy complications. Conversely,
a failed TOLAC resulting in a cesarean delivery (CD) is associated with greater morbidity
than ERCD.[1 ]
To aid in patient counseling, the Maternal–Fetal Medicine Units (MFMU) Network developed
a prediction model from a large prospective U.S. cohort from 1999 to 2002.[2 ] This model incorporates six maternal variables (age, body mass index [BMI], race,
history of prior vaginal delivery, prior VBAC, and indication for prior cesarean)
obtainable at the first prenatal visit to estimate an individualized, patient-specific
likelihood of a successful VBAC.[3 ] Subsequent studies have evaluated the external validity of this prediction model
among various ethnic and geographic cohorts.[4 ]
[5 ]
[6 ]
[7 ]
[8 ]
[9 ] All of these studies have found the model to be most accurate at higher predicted
success rates, and most studies reported that observed rates were lower if predicted
success was <30 to 40%. However, the majority of these validation studies were performed
in relatively homogenous populations where >70% of patients were of a single dominant
ethnicity.[4 ]
[6 ]
[7 ]
[8 ]
We hypothesized that the accuracy of this model may differ between institutions due
to variations in patient populations. Our primary goal was to determine the applicability
of this VBAC prediction model in an ethnically diverse U.S. population at a single
university-based institution. Our secondary aim was to identify factors associated
with higher- or lower-than-predicted success rates.
Materials and Methods
This study was approved by the Institutional Review Board of the University of California,
Los Angeles (UCLA). UCLA Medical Center is a tertiary referral center with an ethnically
diverse patient population ([Table 1 ]). The labor and delivery unit manages approximately 1,800 deliveries a year, and
obstetrics and gynecology residents attend all births. Certified nurse midwives (CNMs)
are the primary prenatal and labor provider for approximately 30% of patients.
Table 1
Study population characteristics
Group
Predicted success
n
Low
<35%
n = 30
Moderate
35–65%
n = 229
High
>65%
n = 309
Total
n = 568
p- Value[a ]
Maternal age (y)
33 ± 4.5
31.6 ± 5.3
32.1 ± 5.2
31.9 ± 5.2
0.279
BMI (kg/m2 )b
37.13 ± 7.9
28.24 ± 5.1
26.09 ± 5.6
27.54 ± 6.1
<0.001
Ethnicity
Caucasian
2
(6.7%)
61
(26.6%)
144
(46.6%)
207
(36.4%)
<0.001
African-American
4
(13.3%)
16
(7%)
11
(3.6%)
31
(5.5%)
Hispanic/Latina
24
(80%)
122
(53.3%)
83
(26.9%)
229
(40.3%)
Asian
0
(0.0%)
15
(6.6%)
27
(8.7%)
42
(7.4%)
Other
0
(0.0%)
15
(6.6%)
44
(14.2%)
59
(10.4%)
Any prior VD
0
(0.0%)
14
(6.1%)
152
(49.2%)
166
(29.2%)
<0.001
Prior VBAC
0
(0.0%)
4
(1.7%)
117
(37.9%)
121
(21.3%)
<0.001
Number of prior CDs
1
29
(96.7%)
221
(96.5%)
295
(95.5%)
545
(96%)
0.82
2
1
(3.3%)
8
(3.5%)
14
(4.5%)
23
(4%)
Indication for prior CD
Arrest of dilation
16
(53.3%)
82
(35.8%)
19
(6.1%)
117
(20.6%)
<0.001
Arrest of descent
7
(23.3%)
54
(23.6%)
18
(5.8%)
79
(13.9%)
NRFHT
2
(6.7%)
38
(16.6%)
93
(30.1%)
133
(23.4%)
Malpresentation
2
(6.7%)
27
(11.8%)
80
(25.9%)
109
(19.2%)
Other
3
(10%)
28
(12.2%)
99
(32%)
130
(22.9%)
Abbreviations: BMI, body mass index; CD, cesarean delivery; NRFHT, nonreassuring fetal
heart tracing; VD, vaginal delivery; VBAC, vaginal birth after cesarean.
Note: Data are represented as mean ± standard deviation or n (%).
a
p -Values were calculated by analysis of variance or chi-squared analysis as appropriate.
b BMI was based on earliest recorded BMI in the pregnancy.
All women who attempted a TOLAC between May 2007 and January 2015 were identified
through the departmental delivery registry. The following patients were excluded:
<18 years of age, fetal demise, lethal fetal anomalies, or incomplete medical records.
The following maternal characteristics (used in the MFMU prediction model)[2 ]
[3 ] were obtained from medical records: maternal age, BMI (kg/m2 ), ethnicity, any prior vaginal delivery, prior VBAC, and indication for prior CD.
If prepregnancy BMI was not available, the earliest available BMI calculation in pregnancy
was used.
To explore the predictive value of factors that were not included in the MFMU model,
additional data were examined. These included (1) antepartum variables, such as, chronic
hypertension, diabetes, number of prior cesarean deliveries, and CNM or physician
as primary prenatal and/or labor provider; (2) intrapartum variables such as spontaneous
onset or induction of labor, augmentation of labor, epidural use, complications including
chorioamnionitis, elevated blood pressures during labor (defined as systolic blood
pressure ≥140 or diastolic blood pressure ≥90), and administration of magnesium sulfate,
and (3) delivery variables such as gestational age at delivery, mode of delivery,
and indication for repeat CD. If the repeat CD was performed after patient request,
without a clear obstetric indication, it was considered elective. The following postpartum
outcomes were collected: birth weight, Apgar scores, symptomatic uterine rupture (confirmed
in the operative report), and postpartum hemorrhage (defined as blood loss >500 mL
for vaginal delivery or >1,000 mL for CD).
Each patient's predicted VBAC success rate was calculated with the online MFMU VBAC
calculator.[3 ] Participants were then stratified into three groups representing “low” (<35%), “moderate”
(35–65%), and “high” (>65%) predicted probability of success. These definitions were
selected based on prior validation studies that showed differential performance of
the model if the predicted success rate was either <30 to 40% or >60 to 70%.[4 ]
[5 ]
[6 ]
[7 ]
[8 ]
[9 ] For each group, we calculated the mean predicted VBAC success rate from the individual
patient scores and the observed success rate for each group. A two-tailed, one-way
test of proportions was used to compare the mean predicted VBAC success probabilities
of each of the three groups to the corresponding observed success rates. Analysis
of variance or chi-squared analysis was used as appropriate to calculate p -values for continuous and noncontinuous variables, respectively. Backward stepwise
logistic regression was performed to identify factors associated with successful VBAC;
results were confirmed with tests for both specification error and goodness of fit.
Stata 13.1 (College Station, TX) was used for all statistical analysis.
Results
During the study period, 595 women met the inclusion criteria and were examined for
eligibility. Two patients were excluded for fetal demise, two patients were under
the age of 18, and three patients were excluded for lethal fetal anomalies. Twenty
patients had incomplete records. In total, 568 (95.4%) women were confirmed eligible
and included in the analysis. In all, 402 women (70.8%) had successful VBAC. A flow
diagram of the final study population is depicted in [Fig. 1 ].
Fig. 1 Flow of study participants. CD, cesarean delivery; TOLAC, Trial of labor after cesarean;
VBAC, vaginal birth after cesarean.
The predicted VBAC success rate was calculated for each patient, with a range of 17.1
to 96.3%. Patients were then stratified into three groups by predicted success rate:
“low” (<35%; n = 30), “moderate” (35–65%; n = 229), and “high” (>65%; n = 309). Descriptive characteristics of the participants are presented in [Table 1 ]. As expected, based on the variables included in the MFMU model, women in the low
group were more likely to be obese, Latina or African-American, or have a recurring
indication for CD. Women in the high group were more likely to have had a prior vaginal
delivery or prior VBAC. Maternal age did not segregate with the predicted likelihood
of success (p = 0.279).
For each group, the mean predicted VBAC success rates were calculated and compared
with the mean actual VBAC success rate ([Fig. 2 ]). For the low group, the mean predicted success rate was 29% and the actual VBAC
success rate was 57%, nearly twofold higher than estimated by the prediction model
(p = 0.001; 95% confidence interval [CI]: 39–75%). For the moderate group, there was
a 9% difference in predicted versus actual success rates (52 vs. 61%; p = 0.006; CI: 55–67%). There was no significant difference between predicted and actual
success rates in the high group (79 and 79%; p = 0.989; CI: 75–84%). For the total cohort, the actual success rate was 71% compared
with the predicted rate of 66% (p = 0.016; CI: 67–75%).
Fig. 2 Vaginal birth after cesarean (VBAC) outcomes by group. Mean predicted and actual
VBAC rates of the low (<35%), moderate (35–65%), and high (>65%) predicted success
groups and for the overall cohort. p- Values were calculated by two-tailed, one-way test of proportions.
Given the finding of higher than predicted VBAC success rates in the low and moderate
groups, we compared intrapartum variables between groups to assess for potential confounding
factors ([Table 2 ]). The rates of spontaneous onset, induction, and augmentation of labor were similar
between the three groups. There was no difference in rates of preterm pregnancy or
in birth weight. The incidence of diabetes was higher in the low group as compared
with the moderate and high groups (23.3, 8.7, and 6.8%, respectively; p = 0.008). The low and moderate groups had higher rates of epidural use in labor compared
with the high group (83.3, 81.7, and 72%, respectively; p = 0.031). The percentage of patients managed by CNMs was not different between groups.
Finally, there was no difference in the rates of intrapartum magnesium administration,
chorioamnionitis, or elevated blood pressure between groups. No patients with multiple
gestations or more than two prior CD attempted TOLAC.
Table 2
Intrapartum variables by predicted success of VBAC
Group
Predicted success
n
Low
<35%
n = 30
Moderate
35–65%
n = 229
High
>65%
n = 309
Total
n = 568
p- Value[a ]
Spontaneous labor
24
(80%)
184
(80.3%)
248
(80.3%)
456
(80.3%)
0.999
Induction
6
(20%)
45
(19.7%)
61
(19.7%)
112
(19.7%)
0.999
Augmentation
17
(56.7%)
115
(50.2%)
136
(44%)
268
(47.2%)
0.157
Preterm pregnancy (<37 wk)
2
(6.7%)
9
(3.9%)
20
(6.5%)
31
(5.5%)
0.42
Diabetesb
7
(23.3%)
20
(8.7%)
21
(6.8%)
48
(8.5%)
0.008
Birth weight (g)
3,402 ± 432
3,431 ± 549
3,428 ± 520
3,422 ± 527
0.934
Labor epidural
25
(83.3%)
187
(81.7%)
224
(72.5%)
436
(76.8%)
0.031
CNM as primary provider
6
(20%)
68
(29.7%)
92
(29.8%)
166
(29.2%)
0.521
Elevated blood pressurec
6
(20%)
19
(8.3%)
25
(8.1%)
50
(8.8%)
0.084
Intrapartum magnesium
3
(10%)
14
(6.1%)
12
(3.9%)
29
(5.1%)
0.233
Chorioamnionitis
2
(6.7%)
21
(9.2%)
13
(4.2%)
36
(6.3%)
0.065
Abbreviations: CNM, certified nurse midwife; VBAC, vaginal birth after cesarean.
Note: Data are represented as mean ± standard deviation or n (%).
a
p -Values were calculated by analysis of variance or chi-squared analysis as appropriate.
b Pregestational or gestational diabetes. c Defined as systolic blood pressure ≥140 and/or diastolic blood pressure ≥90.
Perinatal outcomes stratified by group are presented in [Table 3 ]. The indication for repeat CD varied between the groups (p < 0.001). Patients in the low group had a higher rate of CD for arrest of dilation,
whereas patients in the high group were more likely to have CD for nonreassuring fetal
heart tracing. There was no difference in the rate of 5-minute Apgar score <7 (p = 0.332). There were 10 cases of uterine rupture (10/402; 1.8%), none of which resulted
in a peripartum hysterectomy. The rate of postpartum hemorrhage was greatest in the
low group (20, 17, and 7.8% for the low, moderate, and high groups, respectively;
p = 0.002). There were no maternal or neonatal deaths.
Table 3
Perinatal outcomes by predicted success of VBAC
Group
Predicted success
n
Low
<35%
n = 30
Moderate
35–65%
n = 229
High
>65%
n = 309
Total
n = 568
p- Value[a ]
VBAC
17
(56.7%)
140
(61.1%)
245
(79.3%)
402
(70.8%)
<0.001
Indication for repeat CD
13
(43.3%)
89
(38.9%)
64
(20.7%)
166
(29.2%)
<0.001
Arrest of dilation
5
(38.5%)
29
(32.6%)
18
(28.1%)
52
(31.3%)
Arrest of descent
3
(23.1%)
24
(27%)
14
(21.9%)
41
(24.7%)
NRFHT
3
(23.1%)
26
(29.2%)
23
(35.9%)
52
(31.3%)
Elective
0
(0.0%)
6
(6.7%)
5
(7.8%)
11
(6.6%)
Other
2
(15.4%)
4
(4.5%)
4
(6.3%)
10
(6%)
5-min Apgar <7
1
(3.3%)
7
(3.1%)
4
(1.3%)
12
(2.1%)
0.332
Uterine rupture
1
(3.3%)
6
(2.6%)
3
(1%)
10
(1.8%)
0.283
Postpartum hemorrhage
6
(20%)
39
(17%)
24
(7.8%)
69
(12.1%)
0.002
Abbreviations: CD, cesarean delivery; NRFHT, nonreassuring fetal heart tracing; VBAC,
vaginal birth after cesarean.
Data are represented as mean ± standard deviation or n (%).
a
p -Values were calculated by analysis of variance or chi-squared analysis as appropriate.
We next examined the patient and perinatal factors grouped by VBAC success versus
failure in our overall cohort ([Table 4 ]). Consistent with prior studies,[2 ]
[10 ] the successful VBAC group had lower rates of advanced maternal age (AMA) and higher
rates of prior VD and prior VBAC. The percentage of patients with a recurring indication
for CD (arrest of dilation or descent) was lower in the group that had successful
VBAC. In contrast with the MFMU cohort, there was no difference in BMI or ethnicity
between VBAC success and failure. Birth weight > 4,000 g was more common in failed
TOL, as well as rates of chorioamnionitis, postpartum hemorrhage, and uterine rupture.
There were no differences between the two groups for CNM as primary obstetric provider,
epidural use, preterm pregnancy, diabetes, elevated blood pressures, intrapartum magnesium
administration, and low 5-minute Apgar score.
Table 4
Patient characteristics, obstetric factors, and perinatal outcomes by VBAC success
Total
(n = 568)
VBAC
(n = 402)
Failed TOL
(n = 166)
p- Value[a ]
Advanced maternal age (≥35 y)
193
(34%)
125
(31.1%)
68
(41%)
0.024
BMI (kg/m2 ) ≥30b
185
(32.6%)
130
(32.3%)
55
(33.1%)
0.854
Ethnicity
Caucasian
207
(36.4%)
152
(37.8%)
55
(33.1%)
0.34
African-American
31
(5.5%)
19
(4.7%)
12
(7.2%)
Hispanic/Latina
229
(40.3%)
160
(39.8%)
69
(41.6%)
Asian
42
(7.4%)
33
(8.2%)
9
(5.4%)
Other
59
(10.4%)
38
(9.5%)
21
(12.7%)
Any prior VD
166
(29.2%)
142
(35.3%)
24
(14.5%)
<0.001
Prior VBAC
121
(21.3%)
109
(27.1%)
12
(7.2%)
<0.001
Indication for prior CD
Arrest of dilation
117
(20.6%)
77
(19.2%)
40
(24.1%)
<0.001
Arrest of descent
79
(13.9%)
46
(11.4%)
33
(19.9%)
NRFHT
133
(23.4%)
105
(26.1%)
28
(16.9%)
Malpresentation
109
(19.2%)
81
(20.1%)
28
(16.9%)
Other
130
(22.9%)
93
(23.1%)
37
(22.3%)
Labor type
Spontaneous
456
(80.3%)
336
(83.6%)
120
(72.3%)
0.002
Induction
112
(19.7%)
66
(16.4%)
46
(27.7%)
0.002
Augmentation
268
(47.2%)
165
(41%)
103
(62%)
<0.001
Preterm pregnancy (<37w)
31
(5.5%)
25
(6.2%)
16
(9.6%)
0.214
Diabetesc
48
(8.5%)
34
(8.5%)
14
(8.4%)
0.99
Birth weight (g)
< 2,500
22
(3.9%)
20
(5%)
2
(1.2%)
0.001
2,500–3,999
473
(83.3%)
342
(85.1%)
131
(78.9%)
≥ 4,000
73
(12.9%)
40
(10%)
33
(19.9%)
Labor epidural
436
(76.8%)
301
(74.9%)
135
(81.3%)
0.1
CNM as primary provider
166
(29.2%)
116
(28.9%)
50
(30.1%)
0.76
Elevated blood pressured
50
(8.8%)
35
(8.7%)
15
(9%)
0.9
Intrapartum magnesium
29
(5.1%)
20
(5%)
9
(5.4%)
0.826
Chorioamnionitis
36
(6.3%)
18
(4.5%)
18
(10.8%)
0.005
Complications
5-min Apgar <7
12
(2.1%)
7
(1.7%)
5
(3%)
0.338
Postpartum hemorrhage
69
(12.1%)
26
(6.5%)
43
(25.9%)
<0.001
Uterine rupture
10
(1.8%)
3
(0.7%)
7
(4.2%)
0.004
Abbreviations: AMA, advanced maternal age; BMI, body mass index; CD, cesarean delivery;
CNM, certified nurse midwife; NRFHT, nonreassuring fetal heart tracing; TOL, trial
of labor; VBAC, vaginal birth after cesarean; VD, vaginal delivery.
Note: Data are represented as mean ± standard deviation or n (%).
a
p -Values were calculated by analysis of variance or chi-squared analysis as appropriate.
b BMI was based on earliest recorded BMI in the pregnancy. c Pregestational or gestational diabetes. d Defined as systolic blood pressure ≥140 and/or diastolic blood pressure ≥90.
Unadjusted odds ratios were calculated for these perinatal factors and VBAC success
([Table 5 ]). Of note, there were no associations between VBAC success, and BMI, ethnicity,
CNM as labor provider, epidural use, preterm pregnancy, diabetes, elevated blood pressures,
or intrapartum magnesium administration. Factors negatively associated with VBAC success
were AMA, prior CD for arrest of descent, induction or augmentation of labor, birth
weight > 4,000 g, chorioamnionitis, postpartum hemorrhage, and uterine rupture. VBAC
success was positively associated with a history of prior VD, prior VBAC, prior CD
for nonreassuring fetal heart tracing, and birth weight < 2,500 g. Logistic regression
found that only augmentation of labor and AMA made a significant contribution to the
model; this was confirmed using tests for both specification error and goodness of
fit.
Table 5
Obstetrical variables and successful VBAC
Odds ratio (95% CI)
Advanced maternal age (≥35 y)
0.65 (0.45–0.95)
BMI (kg/m2 ) ≥30[a ]
0.96 (0.66–1.42)
Ethnicity
Caucasian
1.23 (0.84–1.79)
African-American
0.64 (0.31–1.32)
Hispanic/Latina
0.93 (0.64–1.34)
Asian
1.56 (0.74–3.28)
Other
0.72 (0.41–1.26)
Any prior VD
3.23 (2.00–5.21)
Prior VBAC
4.77 (2.57–8.85)
Indication for prior CD
Arrest of dilation
0.75 (0.48–1.15)
Arrest of descent
0.52 (0.32–0.85)
NRFHT
1.73 (1.1–2.73)
Malpresentation
1.24 (0.78–2.00)
Other
1.05 (0.68–1.61)
Labor type
Spontaneous
1.95 (1.27–3.00)
Induction
0.51 (0.33–0.79)
Augmentation
0.43 (0.29–0.62)
Preterm pregnancy (<37w)
1.76 (0.73–4.27)
Diabetesb
1.00 (0.52–1.92)
Birth weight (g)
< 2,500
4.29 (1.1–12.46)
2,500–3,999
1.52 (0.96–2.41)
≥ 4,000
0.45 (0.27–0.73)
Labor epidural
0.68 (0.44–1.07)
CNM as primary provider
0.94 (0.63–1.4)
Elevated blood pressurec
0.96 (0.51–1.81)
Intrapartum magnesium
0.91 (0.41–2.05)
Chorioamnionitis
0.39 (0.2–0.76)
Complications
5-min Apgar <7
0.57 (0.18–1.82)
Postpartum hemorrhage
0.20 (0.12–0.34)
Uterine Rupture
0.17 (0.04–0.67)
Abbreviations: BMI, body mass index; CD, cesarean delivery; CI, confidence intervals;
CNM, certified nurse midwife; NRFHT, nonreassuring fetal heart tracing; VBAC, vaginal
birth after cesarean; VD, vaginal delivery.
Note: CIs that do not cross 1.0 are shown in bold.
a BMI was based on earliest recorded BMI in the pregnancy. b Pregestational or gestational diabetes. c Defined as systolic blood pressure ≥140 and/or diastolic blood pressure ≥90.
Discussion
In summary, we evaluated the MFMU VBAC prediction model in an ethnically diverse U.S.
population at a single university-based hospital. In patients with <65% predicted
probability of success, the actual VBAC rates were significantly higher in our cohort.
The outcomes were most striking for the group with predicted success rates <35%, for
which observed VBAC success rates were 28% higher than predicted. Two of the six patient
characteristics (BMI and ethnicity) used in the published prediction model were not
predictive of VBAC success.
Overall VBAC success rates have been reported to be 60 to 80%.[11 ] The model developed by the MFMU was based on a large U.S. cohort.[2 ] To date, this model has been validated in multiple independent studies, some showing
better model performance at low predicted success rates[4 ] and others showing better performance at higher predicted probability.[5 ]
[6 ]
[7 ]
[8 ]
[9 ] Our study adds to the current literature on the clinical use of this model. In contrast
to published studies, which reported lower actual VBAC rates at lower predicted probabilities,
the model greatly underestimated the probability of success in our study's low group.
Patient ethnicity and BMI, two predictors of VBAC success in the model, were not associated
with success in our cohort. In contrast to the original MFMU cohort and subsequent
validation cohorts, we had more patients of Latina, Asian, and other non-Caucasian
ethnicities, and fewer African-Americans. The prepregnancy BMI, used in the MFMU model,
was not available for all of our patients. As is commonly done in clinical practice,
we used the earliest recorded BMI in pregnancy, which may have contributed to differing
results.
The most serious complication of TOLAC is uterine rupture, a risk that increases with
the number of prior CD.[1 ]
[11 ] Our overall VBAC success rate of 71% was coupled with an overall uterine rupture
rate of 1.8%. Uterine rupture was associated with higher maternal morbidity, including
TOLAC failure and postpartum hemorrhage. Of note, all cases of uterine rupture occurred
in patients with only one prior CD. There were no hysterectomies, maternal deaths,
nor neonatal deaths.
The ethnically diverse cohort described in our study is representative of many areas
of the United States. The broad inclusion criteria, including preterm deliveries and
more than one prior CD, increase our study's generalizability. Our patient cohort
also has a large percentage of patients (10%) with a predicted score of <40%. The
primary limitation of our study is possible selection bias due to the retrospective
design. Our study is not powered to completely exclude associations with variables
reported in this and prior studies.[12 ]
Likely, additional unmeasured variables also influence VBAC outcomes, such as patient
preferences, provider characteristics, and obstetric practice variations. Interestingly,
no patients in the low group chose to end their TOLAC and undergo ERCD (vs. 6.7 and
7.8% in the moderate and high groups, respectively), suggesting that patients in this
group were highly motivated to achieve a VBAC despite a low prediction score. Furthermore,
patients that chose a CNM as their provider may have had a stronger preference for
vaginal delivery. Although a large percentage of our cohort (29%) was managed by CNMs,
we found no association between VBAC success and provider type. Provider management
styles may contribute to TOLAC success, as a recent study showed that providers with
greater coping skills and lower anxiety levels had higher rates of VBAC.[12 ]
Lastly, institutional culture and local practice patterns could influence VBAC success
rates. Fagerberg et al improved the predictive accuracy of the model by incorporating
specific delivery ward CD rates into the algorithm.[8 ] At our institution, TOLAC counseling is performed early in prenatal care by the
primary obstetric provider. TOLAC is encouraged by the majority of providers, although
we do not have data on TOLAC uptake rates. While styles may vary slightly among providers,
our management of induction and augmentation of labor in TOLAC patients relies on
Foley balloon and/or oxytocin. Tertiary referral hospitals equipped with resources
to deal with obstetric emergencies may have increased institutional support of higher
risk TOLACs, leading to improved success rates. Furthermore, data from which the MFMU
model was derived were collected from 1999 to 2002, and obstetric management guidelines
have since evolved to encourage a more permissive definition of normal labor progression.[13 ]
[14 ]
Prior studies have reported that the risk–benefit ratio for TOLAC versus ERCD shifts
in favor of ERCD at predicted success rates of less than 70%.[15 ] Patients may be influenced away from TOLAC in the setting of low predicted success.
Indeed, most studies have shown a low rate of TOLACs with predicted VBAC success <40%,
ranging from 0 to 8%.[4 ]
[5 ]
[6 ]
[7 ]
[8 ]
[9 ] Nevertheless, we show that successful VBAC rates of almost 60% can be achieved despite
predicted rates of <35%. As part of efforts to safely decrease cesarean rates in the
United States, patients interested in TOLAC (and their providers) should not be discouraged
by a low predicted success score.
