Outcomes of Neuraxial Anesthetic Technique on the Trial of Labor After Cesarean (TOLAC): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Outcomes of Neuraxial Anesthetic Technique on the Trial of Labor After Cesarean (TOLAC) (NCT02105558), a randomized phase 4 study. The primary outcome is Number of Participants With Vaginal Birth After Cesarean (VBAC).

2. Clinical Question

In statistical terms, the study addresses an outcome relevant to the success of TOLAC, not simply the immediate quality of pain relief. Its primary endpoint is a participant count, while the secondary outcomes include pain scores, childbirth experience, maternal satisfaction, and neonatal outcome measures. The registry contains numeric comparisons for only some of those secondary outcomes. Thus, the central question concerns the recorded delivery outcome, and the additional measures offer related but incomplete context about analgesia and experience.

3. Trial Design

The registry identifies NCT02105558 as a completed Phase 4 study titled “Outcomes of Neuraxial Anesthetic Technique on the Trial of Labor After Cesarean (TOLAC).” The official title describes it as a pilot study comparing epidural with combined spinal and epidural (CSE) anesthetic technique in relation to TOLAC success. The start is recorded as 2014-04, and primary completion as 2017-04-13. The sponsor is The University of Texas Health Science Center, Houston.

The design is listed as randomized, single masked, and parallel. Random allocation is intended, in general, to make treatment groups comparable on average, while masking can limit some forms of knowledge-related bias. The registry does not report who was masked, how randomization was generated or implemented, or whether allocation concealment was used. Those design details are not reported in the registry record, so the labels alone cannot establish how these protections operated.

Enrollment is recorded as 46. The outcome summaries use their own denominators: for the primary endpoint, the registry reports 15 participants in the epidural group and 28 in the CSE group. Denominators also vary across secondary outcome summaries. The reasons for those differences, including whether they reflect missing outcome data, eligibility for a particular assessment, or another circumstance, are not reported in the registry record.

The study compares two anesthesia techniques within the same broad clinical setting. It is not a comparison of TOLAC with planned cesarean delivery, and the primary outcome does not directly measure pain relief. The registry marks the study completed, but completion status by itself does not establish that every planned analysis was conducted or reported. The original sample-size justification and detailed statistical analysis plan are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: 46 were enrolled, but only 43 started. Of the 3 who did not start: 1 gave birth before the block placement; 2 were disenrolled, but the reason was not recorded.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Vaginal Birth After Cesarean (VBAC), measured over at the time of delivery.

The primary endpoint is the number of participants with vaginal birth after cesarean (VBAC), measured at the time of delivery. It is a binary outcome at the participant level: a participant either had a recorded VBAC or did not. The registry expresses the primary outcome as a count, with the number assessed in each group also reported. This makes the endpoint directly interpretable as the occurrence of vaginal birth after a prior cesarean in the context of TOLAC.

In general, a binary delivery outcome can summarize whether the labor attempt ended in vaginal birth, without implying that all other aspects of care or experience were the same. It is distinct from an analgesia score: pain ratings describe a measured experience at a specified assessment, whereas VBAC records a delivery outcome. The primary endpoint is relevant to the stated study question because the official title and brief summary focus on anesthetic technique and TOLAC success.

The registry does not provide a fuller endpoint definition, adjudication procedure, or details about how a delivery was classified when information was incomplete. These details are not reported in the registry record. The posted result should therefore be read as the recorded count comparison rather than as evidence about unreported delivery characteristics or other maternal and neonatal outcomes.

7. Results Posted in the Registry

• Combined Spinal and Epidural (CSE) Anesthesia: 78.6% (22/28) versus 80.0% (12/15) on control; risk difference -1.4 percentage points (95% CI -26.7 to 23.9), risk ratio 0.98 (0.71–1.35); unadjusted two-proportion z-test p = 0.913.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Success of Analgesia as Indicated by Pain Score Assessed by Visual Analogue Scale (VAS)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Combined Spinal and Epidural (CSE) Anesthesia: mean 8.20 versus 7.53 on control; difference 0.67 (95% CI -0.84 to 2.18), standardized effect d = 0.31; z-test p = 0.384.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Combined Spinal and Epidural (CSE) Anesthesia and the control. The interval gives the range of effects that remain compatible with the data.

Childbirth Experience as Assessed by a Visual Analogue Scale (VAS)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Combined Spinal and Epidural (CSE) Anesthesia: mean 9.25 versus 8.25 on control; difference 1.00 (95% CI -0.58 to 2.58), standardized effect d = 0.54; z-test p = 0.215.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Combined Spinal and Epidural (CSE) Anesthesia and the control. The interval gives the range of effects that remain compatible with the data.

Maternal Satisfaction as Assessed by a Visual Analogue Scale (VAS)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Combined Spinal and Epidural (CSE) Anesthesia: mean 9.25 versus 8.42 on control; difference 0.83 (95% CI -0.64 to 2.30), standardized effect d = 0.44; z-test p = 0.267.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Combined Spinal and Epidural (CSE) Anesthesia and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary results cover pain score at baseline, childbirth experience assessed 24 hours after regional anesthesia, and maternal satisfaction assessed 24 hours after regional anesthesia. Their estimated mean differences are positive for CSE relative to epidural, but the corresponding confidence intervals include zero. The posted p-values are unadjusted. Taken together, these summaries do not establish a clear separation between the techniques on the measured ratings.

These outcomes relate to the primary VBAC result by adding information about reported pain and experience, but they do not measure the same construct. VBAC is a delivery outcome, while the secondary ratings describe participant assessments at specified times. A pattern in one kind of measure cannot be used to infer the other. The baseline pain result in particular is measured before the subsequent experience assessments, and should not be interpreted as a treatment effect arising after anesthesia.

The registry lists additional secondary outcomes, including repeated entries for analgesia assessed by visual analogue scale and a neonatal outcome assessed by APGAR score. Numeric results for those measures are not included among the posted secondary summaries. Their results, timing details beyond the listed outcome labels, and analysis methods are not reported in the registry record.

In general, multiple outcomes create a multiplicity concern: the more comparisons made, the more opportunities there are for chance findings to appear noteworthy. Because adjustment for multiple comparisons and a hierarchy of secondary outcomes are not reported in the registry record, each unadjusted result carries less confirmatory weight than a prespecified, multiplicity-controlled analysis would. The secondary results are best treated as descriptive and hypothesis-generating. They neither overturn nor validate the primary comparison, and they do not establish that the groups have equivalent experiences.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Success of Analgesia as Indicated by Pain Score Assessed by Visual Analogue Scale (VAS)
• Success of Analgesia as Indicated by Pain Score Assessed by Visual Analogue Scale (VAS)
• Success of Analgesia as Indicated by Pain Score Assessed by Visual Analogue Scale (VAS)
• Success of Analgesia as Indicated by Pain Score Assessed by Visual Analogue Scale (VAS)
• Success of Analgesia as Indicated by Pain Score Assessed by Visual Analogue Scale (VAS)
• Childbirth Experience as Assessed by a Visual Analogue Scale (VAS)
• Maternal Satisfaction as Assessed by a Visual Analogue Scale (VAS)
• Neonatal Outcome as Assessed by (APGAR) Score

9. Statistical Interpretation

10. Statistical Methods Explained

What does a risk difference express?

For a binary endpoint, a risk difference compares the proportion with the outcome in one group against the proportion in the other. Here, the posted contrast is CSE relative to epidural. A value below zero means the observed proportion in CSE was lower; a value above zero means it was higher. The estimate -0.014 is close to no observed difference, but the confidence interval indicates that the estimate is not precise. In general, an absolute difference is often easier to interpret clinically than a relative measure, though its meaning still depends on the outcome and context.

The registry also gives a relative risk and an odds ratio. In general, the relative risk compares the outcome proportions, while the odds ratio compares the odds. These measures use different scales and can appear to tell the result differently, especially when an outcome is not rare. They should not be treated as additional independent evidence, because they summarize the same group outcomes. Their intervals are important: the posted intervals are wide, so these estimates do not tightly constrain the possible relative effects.

What does a mean difference describe?

For continuous secondary outcomes, the reported mean difference compares the group averages, with CSE as the comparison against epidural. A positive estimate means the recorded mean was higher in CSE for that measure; it does not, by itself, show that a higher score is better. The registry gives means and standard deviations for each group. In general, a standard deviation describes variability among individual scores, rather than uncertainty in the group mean. The standard error, by contrast, describes the estimated sampling variability of a mean. No scale range or clinically important difference is reported in the registry record, so the practical importance of the score differences cannot be determined from these summaries alone.

How should confidence intervals and p-values be read?

In general, a confidence interval gives a range of estimates compatible with the observed data under the analysis assumptions. It is not a guarantee that the true effect lies in that particular interval, and it does not represent the range of individual participant outcomes. When an interval for a difference includes zero, the data are compatible with no difference as well as with differences in either direction across the interval. The p-value measures how unusual the data, or more extreme data, would be under a specified null model. It is not the probability that the null hypothesis is true and does not measure the probability that the finding will replicate.

The posted p-values are unadjusted. Without a reported adjustment plan, they should be interpreted as individual comparisons rather than as a coordinated family of tests. A conventional threshold cannot substitute for examining effect estimates and intervals, especially where the intervals are broad. No adjusted analysis or confirmatory testing strategy is reported in the registry record.

Why do small outcome groups affect interpretation?

In general, estimates based on fewer observations tend to be less precise, particularly for binary outcomes when the number of events is limited. The primary endpoint has group denominators of 15 and 28, and the posted confidence interval for its risk difference spans appreciable negative and positive values. The record does not report a method for adjusting the primary comparison for other variables, nor does it report a model specification. The posted results should therefore be understood as the presented unadjusted group comparison, not as an adjusted causal estimate.

For continuous outcomes, variability in scores and the number assessed both affect the standard error. The reported standard deviations show that individual scores varied within groups. In general, greater variation or fewer observations makes a mean difference harder to estimate precisely. The posted confidence intervals capture uncertainty about the average contrast, while the means and standard deviations describe the observed group summaries. Neither should be read as a complete account of the distribution of individual scores.

What does the planning illustration represent?

In general, a sample-size calculation asks how many participants would be needed under stated assumptions to have a specified chance of detecting a target effect using a stated test. The planning figures associated with these outcomes use two-sided significance level 0.05, equal allocation between the two arms, and a normal approximation. The target effect is expressed as a stated fraction of the observed effect. Such assumptions are simplifying choices; they are not evidence that the original trial used them. The trial's original sample-size justification and design assumptions are not reported in the registry record.

The estimates labelled recalculated are simple unadjusted recalculations from posted summary statistics. They are not a substitute for a sponsor-reported analysis. If a recalculated result were inconsistent with the sponsor's own analysis, the sponsor's own analysis would take precedence. The record marks no discrepancy. These methodological distinctions matter because a compact registry summary does not provide all the details needed to reproduce or fully audit an analysis.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.014, with a 95% confidence interval from -0.267 to 0.239. In general, the interval describes the uncertainty around the estimated group contrast under the assumptions of the analysis. Its inclusion of zero means that the posted data do not rule out no difference. Its extension to negative and positive values also means that lower and higher VBAC proportions in CSE, relative to epidural, remain compatible with the estimate. The interval is wide relative to the point estimate, so the near-zero estimate should not be mistaken for a precise demonstration of similarity.

The relative-risk interval, from 0.714 to 1.351, and odds-ratio interval, from 0.194 to 4.337, also indicate substantial uncertainty on their respective scales. These intervals are alternative views of the same data and should not be counted as independent confirmations. Their breadth is consistent with the limited outcome denominators in the registry summary.

The secondary mean-difference intervals likewise cross zero. For baseline pain, the interval is -0.838 to 2.178; for childbirth experience, it is -0.580 to 2.58; and for maternal satisfaction, it is -0.636 to 2.296. In general, an interval that includes zero does not prove no effect. It indicates that the data have not estimated the direction and size with enough precision to exclude zero under the stated interval procedure.

The registry does not report a prespecified clinically important difference or scale interpretation that would identify which values within these intervals matter to patients or clinicians. Consequently, statistical precision and practical importance cannot be fully connected from the record. The posted estimates should be read as uncertain comparisons, not as a conclusive ranking of the anesthesia approaches.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are illustrative estimates for a future study under stated assumptions, not a record of the original study's design. For the primary binary outcome, the figures are participants per arm, not total events. The calculation assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and a target effect equal to the stated fraction of the observed effect. The registry's own original sample-size assumptions and justification are not reported in the registry record.

For the primary outcome, planning for 100% of the observed effect gives 12,632 participants per arm for 80% power and 16,910 participants per arm for 90% power. Planning for 75% of the observed effect gives 22,314 participants per arm for 80% power and 29,872 participants per arm for 90% power. Planning for 50% of the observed effect gives 49,883 participants per arm for 80% power and 66,778 participants per arm for 90% power.

In plain language, 80% power means that, if the assumed effect and other calculation assumptions were correct, the design would have an 80% chance of detecting an effect using the specified test. The 90% column describes the corresponding 90% chance under those assumptions. Greater power generally requires more participants when other assumptions are held constant. A smaller target effect is harder to distinguish from random variation, so the illustration calls for more participants per arm as the assumed fraction of the observed effect decreases.

These are not observed power estimates. They do not describe what the completed study achieved, and they should not be interpreted as evidence that the observed result was likely or unlikely. Because they are based on the observed effect, which is uncertain, they are planning illustrations rather than guarantees about a future study. The secondary outcome planning figures likewise use participants per arm for their respective outcomes; the time-to-event convention is not applicable to these posted outcome summaries.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.800; treatment proportion p₁ = 0.786; average p̄ = 0.793.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5731 = 1.1233.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5730 = 0.4823.
4. n = (1.1233 + 0.4823)² / (-0.0143)² = 12,631.6, rounded up to 12,632 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.8                          # control proportion
p1 <- 0.785714285714286                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2105558)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 12,632 (80% power), 16,910 (90% power)
 75% of observed effect: n per arm = 22,314 (80% power), 29,872 (90% power)
 50% of observed effect: n per arm = 49,883 (80% power), 66,778 (90% power)
power.prop.test: 12631.6 
Simulated power at n = 12,632 per arm: 0.796 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry reports no secondary analyses, and a detailed statistical analysis plan is not reported in the registry record. It does not state whether one secondary outcome was designated as more important than the others, whether tests were planned hierarchically, or whether any adjustment for multiple comparisons was intended. Since several secondary outcome measures are listed, unadjusted p-values should not be viewed as if they arose from one isolated test. In general, testing many outcomes without a stated strategy increases the chance that some apparent differences arise from random variation.

Missing-data procedures are not reported in the registry record. The denominators differ across outcome summaries: the primary outcome lists 15 in the epidural group and 28 in the CSE group, while some secondary summaries use different numbers assessed. The reasons for those denominators, how missing observations were handled, and whether any imputation or sensitivity analysis was performed are not reported. Without this information, it is not possible to determine whether the reported groups represent all randomized participants for each outcome or a subset with an available measurement.

The analysis population is also not reported in the registry record. The record does not specify whether analyses followed an intention-to-treat principle, included only participants who received the assigned technique, or used another population definition. It does not describe protocol deviations or crossovers. Such details can affect interpretation in randomized studies because the analysis approach determines which participants contribute to each comparison.

These omissions do not demonstrate that data were missing or that analyses were inappropriate; they indicate that the registry record does not document the relevant methods. The safest reading is limited to the posted outcome counts, summaries, and unadjusted comparisons, without assuming unreported safeguards or procedures.

15. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports no serious adverse events in either group and no deaths. For other adverse events, it records 5 affected participants among 15 at risk in the epidural group and 4 among 28 at risk in the CSE group. These are group-specific recorded counts. The registry does not provide the terms for serious adverse events, and the serious-event term list is empty.

In general, a zero count in a study of this size does not establish that an event cannot occur; it means that no such event was recorded among the participants represented in the posted safety summary. The registry does not report event definitions, severity criteria for other adverse events, timing, relatedness assessments, or whether participants could experience more than one event. Therefore, the counts should not be treated as a complete characterization of the types or comparative risks of adverse events.

The safety summaries are descriptive and do not establish that either anesthesia technique is safer. The denominators and limited detail constrain how precisely the counts can be compared, and the reasons for any variation in safety reporting are not reported in the registry record.

16. What the Result Does, and Does Not, Mean

The posted primary result is a close-to-zero risk-difference estimate for VBAC between CSE and epidural, but its confidence interval is broad. The data are compatible with effects in either direction, and the unadjusted p-value of 0.913 does not establish equivalence. The result therefore describes the comparison observed in this pilot study; it does not settle whether the techniques differ in the wider population of people undergoing TOLAC.

The secondary summaries add observations about pain and participant-reported experience, but they are also imprecise and unadjusted. Their estimated differences do not establish a dependable benefit or disadvantage, and the scale interpretation and clinically important thresholds are not reported in the registry record. The absent numeric results for other listed secondary outcomes further limit an overall account of the study's outcomes.

In general, randomization can support causal interpretation when allocation, follow-up, and analysis are implemented appropriately. The registry identifies randomized allocation, but does not report enough detail to evaluate the sequence generation, concealment, masking procedures, analysis population, or missing-data handling. Consequently, the record supports interpretation of the posted group summaries, while important design and analysis uncertainties remain.

The study's completed status and pilot designation do not make the results definitive. A pilot result can inform the planning of further research, but the observed effect is itself uncertain and should not be treated as a stable estimate. The planning figures are illustrations under stated assumptions, not an account of the trial's original design and not evidence of observed power.

Overall, the registry record does not show a precise or conclusive difference in the primary outcome. It also does not prove that the techniques produce the same outcomes. What can be said is bounded by the posted data: the observed VBAC counts and the calculated contrasts have substantial uncertainty, while several protocol and analysis details are not reported in the registry record.

17. Why This Trial Matters Statistically

This trial illustrates why a point estimate and its uncertainty should be read together. The primary risk difference is near zero, but the confidence interval extends across negative and positive values. Reporting only the point estimate could make the comparison appear more settled than it is; focusing only on the p-value could also obscure the range of effects compatible with the data. The interval communicates that this record does not estimate the contrast precisely.

It also demonstrates the distinction between a clinical endpoint and a statistical measure. VBAC is the primary event of interest, whereas risk difference, relative risk, and odds ratio are different ways of expressing the group comparison. The secondary mean differences concern separate rating outcomes. These measures should not be conflated, nor should multiple summaries of the same endpoint be interpreted as independent findings.

The registry's pilot-study designation is relevant to the role of the results. A small study can contribute useful descriptive information while still leaving substantial uncertainty. Planning estimates based on its observed effects can be especially sensitive to that uncertainty. Clear separation between a planning illustration and an original trial design is therefore important; the original sample-size rationale is not reported in the registry record.

Finally, the record highlights the value of reporting analysis populations, missing-data procedures, outcome hierarchies, and multiplicity plans. Without these details, readers cannot fully evaluate how the posted results relate to all randomized participants or how secondary findings were selected and interpreted. Statistical transparency matters not only for judging significance, but also for understanding the boundaries of what the data can support.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several limitations are specific to the information available for this study. The primary outcome groups have limited denominators, and the resulting risk-difference interval is broad. This limits precision and leaves a wide range of possible differences compatible with the data. The registry labels the study a pilot study, but its original sample-size rationale and intended precision are not reported in the registry record.

The registry identifies a randomized, single-masked design but does not explain the masking procedures, randomization method, or allocation concealment. It also does not report eligibility criteria, participant characteristics, the analysis population, handling of missing data, or treatment of protocol deviations. These omissions prevent a full assessment of comparability, follow-up, and analysis choices from the registry summary.

Outcome denominators vary across the posted summaries, and the reasons are not reported. Several listed secondary outcomes do not have numeric results in the secondary summaries, while the available comparisons are unadjusted and no multiplicity strategy is reported. The registry also does not provide scale ranges or clinically important thresholds for the rating outcomes, making their practical importance difficult to assess.

Safety reporting is limited to group counts, with no serious adverse event terms listed and little detail about event definitions, timing, or relatedness. The posted adverse-event counts therefore cannot fully characterize comparative safety. These limitations describe what is absent from the registry record; they do not establish that the procedures or analyses were not performed.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Outcomes of Neuraxial Anesthetic Technique on the Trial of Labor After Cesarean (TOLAC) — NCT02105558.
• Registry record last updated 2018-07-19; status last verified 2018-06.
• Results first posted 2018-07-19.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT02105558 is a completed Phase 4 randomized, single-masked, parallel pilot study sponsored by The University of Texas Health Science Center, Houston. It compares epidural anesthesia with combined spinal and epidural anesthesia for TOLAC. Enrollment is recorded as 46, and primary completion as 2017-04-13.

The primary endpoint is the number of participants with VBAC at delivery. The registry reports 12 of 15 in the epidural group and 22 of 28 in the CSE group, with a risk difference of -0.014 and a 95% confidence interval from -0.267 to 0.239. Secondary numeric summaries address baseline pain, childbirth experience, and maternal satisfaction; each has an interval that includes zero.

The posted results are uncertain and do not establish either a difference or equivalence. Details including the original sample-size justification, masking procedures, analysis population, missing-data methods, and multiplicity plan are not reported in the registry record.