Ultrasound-Guided Landmark and Epidural Site Pain: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Ultrasound-Guided Landmark and Epidural Site Pain (NCT02813681), a randomized na study. The primary outcome is Epidural Pressure Sensitivity at Level of Epidural Insertion.

2. Clinical Question

The trial focused on localized pressure sensitivity at the insertion site, not generalized postpartum back pain. The registry summary explains that the investigators were interested in short-term sensitivity and its potential relationship to mobility and activities after delivery. It also distinguishes this localized measure from the broader concern that epidural procedures may be blamed for chronic back pain after pregnancy.

That distinction matters when interpreting the question. Comparing ultrasound with sham ultrasound is the direct randomized contrast for the effect of the ultrasound examination process before epidural placement. Comparing either epidural group with participants who did not receive an epidural addresses a broader difference between the groups, including whether an epidural was placed. That broader contrast cannot by itself identify an ultrasound-specific effect.

3. Trial Design

The registry describes NCT02813681 as a prospective randomized clinical trial with a parallel-group model and single masking. The allocation is recorded as randomized. The sponsor was The University of Texas Medical Branch, Galveston. The study is listed as completed, with a start date of 2014-05 and primary completion in 2016-05. Phase is recorded as NA.

Three groups are described: ultrasound before epidural placement, a sham ultrasound process with the monitor off before epidural placement, and spontaneous vaginal delivery without an epidural. The stated aim of the first group was to test whether ultrasound-derived landmarks reduce pressure sensitivity; the no-epidural group was described as a baseline. The registry does not identify which party or parties were masked, so the meaning of single masking beyond the registry label is not reported in the registry record.

Enrollment is listed as 80. For the primary outcome, the posted group summaries report 22 participants in the ultrasound group, 28 in the sham group, and 19 in the no-epidural group. The registry record does not explain how the outcome counts relate to the enrollment figure, whether all enrolled participants contributed to each measurement, or how missing observations were handled. Randomization procedures, allocation concealment, eligibility criteria, and the planned allocation ratio are not reported in the registry record.

The primary outcome is a continuous measure summarized as a mean with standard error. The stated measurement schedule starts 10 minutes before epidural insertion and continues for 10 minutes on each day after epidural removal for 3 days. The record does not specify which time point or summary across times corresponds to the posted group means. Secondary outcomes include labor opioid use, short-term back pain, needle repositions, needle insertions, and induction medication; posted outcome summaries are not available for every listed secondary outcome.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: pressure sensitivity at level of epidural insertion will be measured at epidural insertion site level.

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.

Population: The number of participants who elected to get an epidural proceed to spontaneous vaginal surgery

6. Primary Endpoint

The registry lists the primary outcome as Epidural Pressure Sensitivity at Level of Epidural Insertion, measured over Epidural pressure sensitivity was monitored 10 minutes prior to epidural insertion and then for 10 minutes on each day after epidural removal for 3 days..

The primary endpoint is pressure sensitivity at the level of the epidural insertion site. The registry says it was measured using an algometer and describes the unit as force (newtons/cm^2). The outcome is recorded as a continuous measure, with a mean and standard error for each group. The posted mean is 26.8 for the ultrasound group and 26.8 for the sham group; the no-epidural group's posted mean is 47.6.

The stated measurement schedule begins 10 minutes before epidural insertion and then includes measurements for 10 minutes on each day after epidural removal for 3 days. The rationale was to capture localized pressure sensitivity, a distinct outcome from generalized postpartum back pain. The registry summary notes interest in short-term sensitivity because it might limit mobility and activities in the postpartum period. This explains why a site-specific pressure measure was selected, but does not establish that the endpoint is a validated measure of mobility or of longer-term pain.

The posted result does not identify whether the means represent a particular measurement occasion, an average across occasions, or another summary. Nor does the registry record describe how repeated measurements were analyzed. Consequently, the reported group means can be read as the posted summaries of the endpoint, but their precise timing and construction cannot be inferred. The endpoint is relevant to the study's stated question, while its interpretation depends on measurement details that are not reported in the registry record.

7. Results Posted in the Registry

• US-epidural SVD: mean 26.80 versus 26.80 on control; difference 0.00 (95% CI -7.84 to 7.84), standardized effect d = 0.00; z-test p = 1.000.
• Spontaneous Vaginal Delivery Without an Epidural: mean 47.60 versus 26.80 on control; difference 20.80 (95% CI 14.28 to 27.32), standardized effect d = 1.78; z-test p = <0.001.

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.

Opioid Use During Labor

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • US-epidural SVD: 27.3% (6/22) versus 32.1% (9/28) on control; risk difference -4.9 percentage points (95% CI -30.3 to 20.5), risk ratio 0.85 (0.36–2.02); unadjusted two-proportion z-test p = 0.709.
  • Spontaneous Vaginal Delivery Without an Epidural: 47.4% (9/19) versus 32.1% (9/28) on control; risk difference 15.2 percentage points (95% CI -13.1 to 43.6), risk ratio 1.47 (0.72–3.02); unadjusted two-proportion z-test p = 0.292.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between US-epidural SVD and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Spontaneous Vaginal Delivery Without an Epidural and the control. The interval gives the range of effects that remain compatible with the data.

Short-term Back Pain

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • US-epidural SVD: 18.2% (4/22) versus 25.0% (7/28) on control; risk difference -6.8 percentage points (95% CI -29.6 to 15.9), risk ratio 0.73 (0.24–2.17); unadjusted two-proportion z-test p = 0.563.
  • Spontaneous Vaginal Delivery Without an Epidural: 36.8% (7/19) versus 25.0% (7/28) on control; risk difference 11.8 percentage points (95% CI -15.1 to 38.8), risk ratio 1.47 (0.62–3.52); unadjusted two-proportion z-test p = 0.384.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between US-epidural SVD and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Spontaneous Vaginal Delivery Without an Epidural and the control. The interval gives the range of effects that remain compatible with the data.

Number of Needle Repositions

• 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 errors.
• Result:
  • US-epidural SVD: mean 0.80 versus 2.20 on control; difference -1.40 (95% CI -2.02 to -0.78), standardized effect d = -1.14; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for US-epidural SVD than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary outcomes add context but do not resolve the primary question. The registry lists labor opioid use, short-term back pain, needle repositions, needle insertions, and induction medication. Posted summaries and recalculated comparisons are available for some, while results for every listed outcome are not present. This uneven reporting limits any assessment of whether the full set of secondary findings forms a consistent pattern.

At a broad level, the available secondary summaries do not all have the same statistical character: some are counts of participants with an outcome, and another is a mean count of needle repositions. They address different aspects of care and are not interchangeable measures of insertion-site pressure sensitivity. The direct ultrasound-versus-sham primary comparison remains the most relevant contrast for the effect of the ultrasound examination process. Secondary outcomes may help describe related procedural or postpartum experiences, but they cannot substitute for the primary endpoint.

The secondary comparisons are unadjusted recalculations from posted summaries, and the registry lists no reported analyses. Their p-values and intervals should therefore be read cautiously. When multiple outcomes and comparisons are examined, the opportunity for chance findings increases unless the analysis accounts for multiplicity. No such strategy is reported in the registry record. A finding that appears statistically noteworthy among secondary outcomes would consequently be less persuasive as confirmatory evidence than a prespecified, appropriately analyzed primary result.

The registry does not explain whether these outcomes were prespecified, how the outcomes were defined in practice, or how missing observations were handled. The general pattern should therefore be described as limited and exploratory rather than as a coherent body of evidence supporting a broader conclusion. No secondary result should be used to infer that ultrasound changed the primary endpoint, or that a difference between the no-epidural group and sham was caused by the ultrasound procedure.

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

• Induction Medication
• Opioid Use During Labor
• Short-term Back Pain
• Number of Needle Repositions
• Number of Needle Insertions

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous, so the posted summaries use group means and standard errors. A mean gives the average value in a group, while a standard error describes uncertainty in estimating that group mean. It is not a measure of the spread of individual observations. The posted results do not include standard deviations or individual-level data, so the extent of variation between participants cannot be directly read from these summaries.

What does a mean difference represent?

A mean difference compares the average endpoint value in one group with the average in its reference group. For ultrasound versus sham, the posted means are both 26.8, and the unadjusted recalculated mean difference is 0.0. For the no-epidural group versus sham, the unadjusted recalculated mean difference is 20.8. These are absolute differences in the endpoint's stated units, not relative changes. The meaning of direction depends on the measure and the comparison order; the registry does not state a threshold at which a difference would be clinically important.

The recalculations use posted group summaries and are unadjusted. They are not a substitute for an analysis using participant-level data, especially if the endpoint includes repeated measurements over time. The registry's time frame describes measurements before insertion and after epidural removal, but does not say whether the posted mean is tied to one time point or combines observations. A model that accounts for within-participant correlation over time could produce a different estimate or uncertainty from a simple comparison of group summaries. Whether such a model was planned or used is not reported in the registry record.

How should a p-value be read?

A p-value describes how compatible the observed data are with a specified null hypothesis under the assumptions of the analysis. It does not give the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The primary ultrasound-versus-sham recalculation has p = 1.0 because the estimated difference is 0.0 in these summaries. The no-epidural contrast has p < 0.001. Neither p-value addresses unreported sources of bias, measurement choices, or group differences. The registry does not report adjusted analyses, so these p-values should be understood as unadjusted recalculations rather than the outcome of a documented sponsor analysis.

Why does the confidence interval matter?

A confidence interval is a range of estimates compatible with the data and method at a stated confidence level. It communicates the precision of an estimate as well as its direction. The primary interval extends from -7.84 to 7.84 around the zero difference, so the observed equality of means does not rule out differences in either direction. The interval for the no-epidural comparison lies above zero, but that descriptive contrast has a different causal interpretation from the randomized ultrasound-versus-sham comparison. Confidence intervals do not compensate for limitations in the design or analysis.

What can planning illustrations tell readers?

The planning illustrations are based on the observed effects and are not the trial's own design justification. They use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. For the primary comparison with the no-epidural group, the illustration lists 20 participants per arm for 80% power when planning for 50% of the observed effect. Such figures are planning examples, not observed power, and do not show that the completed trial had a particular probability of detecting an effect. The registry does not report the trial's sample-size assumptions, justification, or planned power.

For binary secondary outcomes, a risk difference is an absolute contrast between group proportions. Its confidence interval can include values in both directions, and the small group summaries can make estimates imprecise. Relative measures such as risk ratios or odds ratios use different scales; they do not replace the absolute difference and may be difficult to interpret when event counts are limited. For continuous secondary outcomes, mean differences compare average counts or values. The registry does not list formal analyses for these secondary results, so recalculated contrasts remain unadjusted summaries rather than confirmatory tests.

Over-dispersion is a general issue for count outcomes: observed counts may vary more than a simple statistical model expects. If that occurs, model-based standard errors can be too small unless the analysis accounts for the extra variation. This is a general consideration for outcomes such as needle repositions, not evidence that over-dispersion occurred in this trial. The registry record does not report a count model or a dispersion assessment.

11. Confidence Intervals and Precision

Precision is most directly expressed by the confidence interval around an estimated difference. For ultrasound versus sham, the unadjusted recalculated mean difference is 0.0 and its 95% confidence interval runs from -7.84 to 7.84. The estimate is centered at no difference, but the interval spans values on both sides of zero. It therefore does not establish equivalence, and its width leaves uncertainty about the size and direction of a possible difference.

For the comparison of the no-epidural group with sham, the unadjusted recalculated mean difference is 20.8, with a 95% confidence interval from 14.28 to 27.32. This interval is separated from zero under the recalculation, but the comparison is not the same randomized contrast as ultrasound versus sham. Precision about a descriptive difference does not remove uncertainty about why the groups differ.

A confidence interval is conditional on the statistical method and data used to construct it. These intervals are recalculated from posted summary statistics, not identified as estimates from a reported sponsor analysis. The registry does not describe adjustment for repeated measurements, covariates, or missing observations. The result summaries also do not specify which scheduled measurement occasion underlies the primary means. These omissions affect how fully the displayed precision can be assessed.

The sample sizes attached to the outcome summaries are limited, and the registry does not provide a clinically meaningful threshold against which to judge the intervals. Thus, the interval for the direct ultrasound comparison should not be reduced to the statement that there is no effect. It indicates an estimated difference of zero with uncertainty extending in both directions. Better precision would require additional information or data; the planning illustrations are hypothetical design aids, not evidence of precision achieved by the trial.

12. Multiplicity, Missing Data and Analysis Populations

The registry record does not report a multiplicity strategy for the primary and secondary outcomes or for the several group comparisons. Multiplicity is the general issue that arises when many statistical tests are considered: without an adjustment or a prespecified hierarchy, the chance of at least one apparently notable result arising by chance can increase. This concern is particularly relevant when interpreting unadjusted secondary comparisons. The registry lists six outcome measures, while posted secondary summaries are available for fewer than all of the named outcomes.

The record does not report a statistical analysis plan, a primary-analysis population, or a rule for handling deviations from assigned groups. Although allocation is described as randomized, the analysis population used for the posted summaries is not stated. It is therefore not possible to determine from the registry whether the results reflect an intention-to-treat analysis, a per-protocol analysis, or another approach. The record does not report how adherence to the assigned procedures was defined or handled.

Missing-data methods are not reported in the registry record. The enrollment figure and the group-specific outcome sample sizes are both recorded, but the registry does not explain the relationship between them or why the outcome counts differ from enrollment. There is no basis to infer whether this reflects missing measurements, exclusions, differences in availability by outcome, or another reason. The missingness mechanism and any imputation or sensitivity analysis are likewise not reported.

The primary measurement schedule involves repeated occasions, but the record does not describe whether all scheduled measures were collected, how they were combined, or how within-participant correlation was handled. Interim analyses, stopping rules, and any prespecified adjustment for repeated looks are not reported in the registry record. These are absences of documentation, not proof that no such procedures existed. They limit the ability to evaluate whether the posted estimates and their uncertainty correspond to the planned analysis.

13. 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.

The registry reports zero serious adverse events in each of the three groups and zero other adverse events in each group. It also reports zero deaths in each group. No serious adverse event terms are listed. These figures describe what was recorded in the registry; they do not establish that no adverse events of any kind occurred outside the definitions, observation period, or reporting process used for the record.

The adverse-event group counts are not accompanied by a description of surveillance, event definitions, severity grading, causal attribution, or duration of follow-up. The registry record does not report how often safety information was collected or how missing safety observations were handled. In particular, the primary outcome's measurement period should not be assumed to be the safety follow-up period.

Zero reported events in the recorded groups should be interpreted as an absence of reported events in this record, not as evidence that the procedures carry no risk. The group sizes are limited, and rare events may not be captured reliably in a trial of this scale. The safety figures are descriptive and do not support a comparative safety conclusion without fuller reporting of ascertainment and follow-up.

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

The primary posted summaries show equal mean pressure sensitivity for the ultrasound and sham groups: 26.8 in each. The unadjusted recalculated mean difference is 0.0, with a 95% confidence interval from -7.84 to 7.84. This is the result most directly relevant to whether the ultrasound examination process changed the endpoint relative to sham. It is an estimate with uncertainty, not proof that the procedures are equivalent or that a possible difference is exactly zero.

The no-epidural group has a higher posted mean than the sham group, and the unadjusted recalculated contrast is 20.8. That comparison involves groups differing in epidural receipt, so it cannot isolate the effect of ultrasound. It is a descriptive group difference and should not be framed as evidence that the ultrasound procedure caused a change in sensitivity.

The endpoint is localized pressure sensitivity at the insertion site. It is not the same as chronic or generalized back pain, and the posted result cannot be extended to those outcomes. The registry explains why short-term sensitivity interested the investigators, but does not report a threshold for clinical importance or show how the measure relates to mobility and activities. The measurement schedule is described, but the time point or summary represented by the posted means is not identified.

The registry also does not report the analysis plan, missing-data approach, or methods for handling repeated observations. The recalculated contrasts are unadjusted and based on summary statistics. Accordingly, the results support a limited reading of the recorded group summaries, not a broad claim about all people receiving epidurals, all ultrasound-guided procedures, or longer-term health effects. The trial's completed status and randomized label do not by themselves settle these interpretive limitations.

15. Why This Trial Matters Statistically

This trial raises a useful statistical distinction between a direct intervention contrast and a baseline comparison. Ultrasound versus sham is the comparison that most clearly isolates the examination process while keeping epidural placement common to both groups. The no-epidural group provides a different reference: it contrasts participants with and without epidural placement. Treating these contrasts as interchangeable would blur the causal question.

The primary result also illustrates why an estimate and its uncertainty should be read together. The point estimate for ultrasound versus sham is zero, but the confidence interval extends in both directions. A zero point estimate is not a demonstration of equivalence, particularly when no equivalence margin is reported. Statistical interpretation requires attention to plausible effect sizes as well as whether a test crosses a conventional significance threshold.

Repeated measurement adds another important issue. The stated outcome schedule includes measurements before insertion and on days after epidural removal, yet the registry does not say how those observations produced the posted group means. Longitudinal measurements from one participant are generally related rather than independent; a suitable analysis needs to account for that structure if multiple occasions are combined. The absence of a reported analysis method prevents readers from assessing this aspect.

Finally, the record demonstrates the limits of registry-level summaries for evaluating completeness and robustness. Enrollment and outcome group counts are both reported, but their relationship is unexplained; the analysis population, missing-data methods, multiplicity approach, and clinically meaningful threshold are not reported. Those details affect precision and interpretation, even when group means and recalculated intervals are available. The statistical value of the record lies in separating what the observed summaries indicate from what remains unestablished.

16. 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 available record for this trial. The endpoint schedule includes measurements before epidural placement and on each day after removal for 3 days, but the result is not tied to a particular occasion or an identified summary over time. Without that information, the primary mean cannot be interpreted as a clearly defined time-specific response or trajectory.

Although the trial is labeled randomized, the registry does not describe the randomization process, sequence generation, allocation concealment, or how assignment was implemented. It also does not identify who was masked. The sham procedure is described as the examination process with the monitor off, but the record does not provide further details that would allow assessment of how closely it matched the active procedure.

Enrollment is listed as 80, while the primary outcome group summaries report 22, 28, and 19 participants. The registry does not reconcile these counts. This makes it difficult to assess the analysis population, exclusions, missing observations, and the extent to which the posted results represent the enrolled participants. No baseline characteristics are posted in the stated details, so comparability of groups on measured characteristics cannot be assessed.

The registry does not report a sample-size justification, a formal analysis plan, a clinically meaningful difference, or a method for accounting for repeated measurements. Recalculated tests use only the group summaries and are unadjusted. The record also lists secondary outcomes without posted results for every outcome, and does not describe outcome definitions or multiplicity control. These limitations constrain causal interpretation, precision assessment, and the ability to judge whether the analysis followed a prespecified plan.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Ultrasound-Guided Landmark and Epidural Site Pain — NCT02813681.
• Registry record last updated 2019-10-03; status last verified 2016-06.
• Results first posted 2019-10-03.
• 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.

20. Record Summary

NCT02813681 is a completed, randomized, parallel-group trial sponsored by The University of Texas Medical Branch, Galveston. The registry records single masking, enrollment of 80, a start date of 2014-05, and primary completion in 2016-05. It compared ultrasound before epidural placement, a sham ultrasound process before epidural placement, and spontaneous vaginal delivery without an epidural.

The primary outcome was pressure sensitivity at the epidural insertion site, measured with an algometer and summarized as a mean with standard error. The ultrasound and sham groups each had a posted mean of 26.8. Their unadjusted recalculated mean difference was 0.0, with a 95% confidence interval from -7.84 to 7.84. The no-epidural group had a posted mean of 47.6.

The record does not identify which measurement occasion is represented by the primary means or report the planned analysis, missing-data methods, multiplicity strategy, or clinically meaningful threshold. The no-epidural comparison is not an ultrasound-specific contrast. Secondary outcomes and safety counts offer descriptive context, but do not resolve these limitations.