Does Ultrasound Help With Placement of Labor Analgesia in Pregnant Patients?: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Does Ultrasound Help With Placement of Labor Analgesia in Pregnant Patients? (NCT02207972), a randomized na study. The primary outcome is Number of Participants With Accurate Epidural Placement.

2. Clinical Question

The clinical question is motivated by the investigators’ stated belief that ultrasound guidance could help place the epidural needle in the midline, with positive cerebrospinal fluid (CSF) in the spinal needle and correct catheter placement. The brief summary also describes adequate, symmetrical labor analgesia or anesthesia as an intended downstream result. Those ideas explain the rationale for studying the technique; they should not be mistaken for separate findings of the primary endpoint. The primary endpoint is the number of participants with accurate epidural placement, not a direct measure of pain relief or symmetry of analgesia.

The registry record lists two additional outcomes: successful placement on the first attempt and success without angle adjustments in space. These outcomes address related aspects of procedural placement, but they do not replace the primary question. The record does not report further eligibility criteria, participant characteristics, or details about the clinical setting beyond the study sponsor and the intervention descriptions. The results therefore describe the recorded groups and outcomes, rather than establishing how the findings apply to patient groups or settings not characterized in the registry record.

3. Trial Design

The registry record describes a randomized, parallel-group study with no masking. It reports enrollment of 46 participants and a completed status. The study began in 2013-05, and primary completion was recorded in 2015-02. Its phase is listed as NA. The sponsor is St. Luke's-Roosevelt Hospital Center. The method used to generate the random allocation sequence, conceal allocation, or implement randomization is not reported in the registry record.

The two arms compared ultrasound-guided CSE placement with CSE placement using palpation of anatomical landmarks. Both arm descriptions state that a continuous epidural infusion was started after placement, with an infusion of 12 ml/hr of 0.062% Bupivacaine and Fentanyl 2mcg/ml. The record does not specify whether other aspects of care were standardized, nor does it provide details about the clinicians performing the procedures or their experience with either approach.

The primary outcome is a participant count for accurate epidural placement, with a timeframe of 2 hours. The registry record also lists two immediate secondary outcomes concerning successful first-attempt placement and placement success without angle adjustments in space. The posted primary outcome counts are 21 of 22 participants in the Use of Ultrasound arm and 23 of 24 in the No Ultrasound Used arm. No separate participant-flow account, exclusions after randomization, or analysis-population definition is reported in the registry record. Although the posted arm counts align with the recorded enrollment, that alone does not establish how missing observations or protocol deviations were handled.

The design supports a direct comparison of the recorded outcomes between the two assigned approaches. With no masking, participants and clinicians would not have been masked to the use of ultrasound; whether outcome assessors were masked is not reported in the registry record. The record does not report the original sample-size justification, allocation ratio rationale, planned interim analyses, or a detailed statistical analysis plan. These omissions limit assessment of how the trial was intended to handle design and analysis choices beyond the randomized, parallel structure it records.

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: Once the patient agrees to be in the study, they will be randomized into one of the 2 arms (with or without ultrasound) for their neuraxial placement.

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 Accurate Epidural Placement, measured over 2 hours.

The primary endpoint is the number of participants with accurate epidural placement, recorded at 2 hours. Its description specifies accurate placement of the ultrasound-guided CSE technique, with the stated placement target being the midline position. In the posted results, 21 participants in the Use of Ultrasound arm and 23 in the No Ultrasound Used arm were recorded as meeting this endpoint.

This endpoint is used to address the procedural question motivating the study: whether ultrasound guidance is associated with accurate midline placement compared with placement based on palpation of anatomical landmarks. Counting participants with the outcome provides a direct summary of how many in each arm met the registry’s stated criterion. It does not, by itself, convey the full range of procedural experience or the certainty around a difference between the approaches; those require comparison estimates and measures of uncertainty.

The endpoint should be distinguished from outcomes that are described as possible consequences of correct placement. The investigators’ brief summary links midline needle placement to positive CSF in the spinal needle, correct catheter placement, and adequate symmetrical labor analgesia or anesthesia. The primary endpoint description does not say that it measures each of those consequences. Nor does its title describe pain relief, analgesia quality, or adverse outcomes. Those outcomes should not be inferred from a count of accurate epidural placements.

The exact operational criteria used to determine “accurate” placement, the assessor, and the method of assessment are not reported in the registry record. That missing detail matters when interpreting what the count represents and how consistently the endpoint could be assessed. The posted result is therefore best read as the registry’s recorded count for this endpoint, rather than as a comprehensive measure of every technical or clinical consequence of the procedure.

7. Results Posted in the Registry

• No Ultrasound Used: 95.8% (23/24) versus 95.5% (21/22) on control; risk difference 0.4 percentage points (95% CI -11.4 to 12.2), risk ratio 1.00 (0.89–1.14); unadjusted two-proportion z-test p = 0.950.

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.

Number of Participants With Successful First Attempt

• 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:
  • No Ultrasound Used: 87.5% (21/24) versus 86.4% (19/22) on control; risk difference 1.1 percentage points (95% CI -18.4 to 20.6), risk ratio 1.01 (0.81–1.27); unadjusted two-proportion z-test p = 0.909.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between No Ultrasound Used and the control. The interval gives the range of effects that remain compatible with the data.

Number of Participants Without Angle Adjustments in Space Success

• 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:
  • No Ultrasound Used: 50.0% (12/24) versus 72.7% (16/22) on control; risk difference -22.7 percentage points (95% CI -50.0 to 4.6), risk ratio 0.69 (0.43–1.11); unadjusted two-proportion z-test p = 0.115.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between No Ultrasound Used and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes concern procedural features that are related to, but distinct from, the primary measure of accurate epidural placement. Taken together, their point estimates do not all point in the same direction: the first-attempt comparison is close to zero, while the outcome concerning success without angle adjustments has a larger point estimate favoring the ultrasound arm under the defined contrast. Their confidence intervals are broad and include zero. This pattern does not provide a consistent, precise account of a difference across all the recorded procedural outcomes.

The secondary outcomes can add context to the primary result by asking whether the placement approaches differed on aspects of the procedure beyond the principal accuracy count. They do not establish the primary endpoint’s measurement validity, nor do they measure downstream analgesia or anesthesia quality as posted. Because they describe different aspects of placement, a difference on one would not automatically imply a difference on another. The relationship between these measures and the hypothesized consequences is not fully specified in the registry record.

Unadjusted secondary results carry less weight because they are additional comparisons and the record does not state how they were prioritized or whether the analysis accounted for multiple testing. When many outcomes are examined, the chance of at least one apparently notable result from random variation can increase. No multiplicity strategy is reported in the registry record. The secondary findings should therefore be treated as exploratory descriptive evidence rather than decisive confirmation of a procedural advantage.

The registry record lists no reported analyses for the secondary endpoints. The estimates described are recalculated unadjusted comparisons from the posted counts. The absence of a reported analysis plan means it is not possible to determine whether these outcomes were prespecified in the form analyzed, how missing observations were treated, or whether there were additional planned secondary measures that were not posted. These limits counsel against selecting one secondary result in isolation to characterize the overall trial.

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

• Number of Participants With Successful First Attempt
• Number of Participants Without Angle Adjustments in Space Success

9. Statistical Interpretation

10. Statistical Methods Explained

For a binary outcome such as whether accurate placement was recorded, each participant is classified as having or not having the outcome. The event count is the number meeting the outcome, and the group size is the number of participants in that arm. The primary endpoint is posted as a count: 21 participants with the outcome among 22 in the Use of Ultrasound arm, and 23 among 24 in the No Ultrasound Used arm. The corresponding observed rates listed for the arms are 0.955 and 0.958. These rates describe the observed groups; they do not alone tell how uncertain a comparison is.

What does the risk difference express?

The risk difference subtracts one group’s event rate from the other’s. In the comparisons for this trial, the direction is No Ultrasound Used minus Use of Ultrasound. Thus a positive value indicates a higher observed rate in the palpation arm, while a negative value indicates a higher observed rate in the ultrasound arm. The primary risk difference is 0.004. This is an absolute contrast between rates, not a relative measure. The sign and size need to be read together with its confidence interval, which communicates uncertainty around the estimate.

What do relative risks and odds ratios add?

A risk ratio compares the event rates by division, while an odds ratio compares the odds of the outcome between groups. Both are relative measures, unlike a risk difference, which is an absolute measure. For the primary endpoint, the posted risk ratio is 1.004, with limits 0.887 and 1.136; the posted odds ratio is 1.095, with limits 0.064 and 18.64. The broad odds-ratio interval illustrates that relative estimates can be especially uncertain when outcome counts are close to the edge of the possible range, as they are for this endpoint. Different effect measures answer different descriptive questions, so they should not be treated as interchangeable.

How should a confidence interval be understood?

A confidence interval is a range of values that reflects the uncertainty in an estimate under the method used to calculate it. It is not a guarantee that the true effect lies within the particular interval, and it does not assign a probability to each value in the range. For a risk difference, zero represents no difference between the group rates. The primary interval, from -0.114 to 0.122, includes zero, so it does not rule out no difference; it also spans values in both directions. Its width shows that the point estimate is much more precise than the data justify if interpreted alone.

What does the p-value describe?

A p-value measures how unusual data at least as discrepant as those observed would be under a specified null model. It is not the probability that the null hypothesis is true, nor is it a direct measure of clinical importance. The primary unadjusted p-value is 0.95. Read alongside the confidence interval and group counts, it indicates that the posted data do not provide evidence of a difference under the unadjusted comparison. It does not establish that there is no difference, and it cannot resolve the uncertainty about the size of a possible effect.

Why can over-dispersion matter in other outcome models?

General statistical context: over-dispersion occurs when observations vary more than a model assumes. It can make standard errors too small if ignored, causing intervals to be too narrow and tests to appear more conclusive than warranted. The outcomes posted for this trial are participant counts for binary endpoints, and the registry record does not report an over-dispersed outcome model. There is no basis in the record to claim that over-dispersion was assessed or found. This concept is relevant when choosing models for count or rate data, but it should not be applied as a diagnosis of these results.

What is meant by an unadjusted recalculation?

The effect estimates and p-values described for this analysis are recalculated unadjusted comparisons from the posted group counts. “Unadjusted” means that the calculations do not account for other participant characteristics or covariates. These summaries are not a substitute for a trial analysis that might adjust for prespecified factors or use a different method. The registry record lists no reported analyses for the secondary endpoints, and it does not provide a detailed statistical plan. The recalculated results should therefore be read as simple comparisons of the posted summaries.

Randomization is intended to support comparability of groups on average, but it does not ensure balance in every characteristic, especially in a small trial. The registry record describes the allocation as randomized but does not describe how randomization was generated or concealed. It also does not state whether the primary endpoint assessor was masked. Those omissions affect the ability to evaluate possible selection or measurement biases from the record alone. The no-masking designation means the study was not masked, but the record does not describe the masking status of each role in more detail.

The outcome counts and comparative estimates answer related but distinct questions. Counts show how many participants met the recorded criterion; group rates express those counts relative to each arm; the risk difference, risk ratio, and odds ratio describe contrasts; and intervals and p-values convey uncertainty or evidence under specific statistical assumptions. None of these quantities alone addresses the clinical meaning of an outcome definition that is not fully specified in the registry record. Statistical interpretation therefore depends on both the numerical comparison and the quality and clarity of the underlying measurement and design information.

11. Confidence Intervals and Precision

The primary risk-difference estimate is 0.004, with a 95% confidence interval from -0.114 to 0.122. The point estimate is close to zero, but the interval extends to values in both directions. It therefore indicates substantial uncertainty about the size and direction of the difference, rather than a precise estimate of no effect. The interval includes zero, which is consistent with no difference under this measure, but also includes other values that represent differences between the groups.

The number of participants in each arm is limited: 22 in Use of Ultrasound and 24 in No Ultrasound Used. When the outcome is recorded for nearly all participants in both groups, the resulting event counts can look very similar, yet the comparison may still be imprecise. The observed counts do not eliminate uncertainty about how the rates might compare beyond these participants. The confidence interval is important because it gives a range of effects compatible with the data and method, not just the single point estimate.

The secondary confidence intervals are also broad. For successful first attempt, the risk-difference interval runs from -0.184 to 0.206. For success without angle adjustments in space, it runs from -0.500 to 0.046. Both include zero and span values in more than one direction. These intervals provide limited precision for distinguishing between the approaches on those outcomes.

Precision is not the same as validity or clinical importance. An interval can be calculated precisely under a statistical method while the endpoint definition, measurement process, or analysis population remains unclear. In this trial, the operational definition and assessment procedure for accurate placement are not reported in the registry record. The numerical intervals should therefore be interpreted with the additional limitation that the measurement details are incomplete. No conclusion about a clinically important threshold can be made because such a threshold is not reported in the registry record.

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 sample-size illustrations express the number of participants per arm for each stated planning scenario. They are not total event counts: the outcomes in this trial are participant-level binary outcomes, and the record’s planning convention assigns participants per arm for outcomes of this type. The registry record does not report the trial’s original sample-size justification or the assumptions used to plan its enrollment.

The planning illustrations use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. The 80% power column represents the planned number of participants per arm under those assumptions to have an 80% chance of detecting the specified effect if that effect is present and the assumptions hold. The 90% power column uses a higher target chance of detection under the same general planning framework. These are design concepts, not guarantees about what a future study will find.

Across the listed scenarios, planning for a smaller fraction of the observed effect requires more participants per arm than planning for the full observed effect. This is because smaller differences are harder to distinguish from random variation. The illustrations are based on the observed effect, which is uncertain in a trial with limited group sizes. They should not be read as a recommended enrollment target without a separate design decision about the effect of interest, outcome definition, analysis, and other assumptions.

The sample-size figures are planning illustrations, not observed power. They do not describe the probability that this completed trial detected an effect after its results were known, and they do not change the uncertainty in the posted estimates. The trial’s own original design assumptions, including any planned target effect, are not reported in the registry record.

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 = 0.955; treatment proportion p₁ = 0.958; average p̄ = 0.956.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.2887 = 0.5658.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.2887 = 0.2429.
4. n = (0.5658 + 0.2429)² / (0.0038)² = 45,581.2, rounded up to 45,582 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 <- 0.954545454545455                          # control proportion
p1 <- 0.958333333333333                          # 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(2207972)
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 = 45,582 (80% power), 61,020 (90% power)
 75% of observed effect: n per arm = 81,875 (80% power), 109,607 (90% power)
 50% of observed effect: n per arm = 186,108 (80% power), 249,145 (90% power)
power.prop.test: 45581.2 
Simulated power at n = 45,582 per arm: 0.800 (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 record lists one primary endpoint and two secondary outcomes, but it does not report a strategy for multiplicity. Multiplicity concerns the increased chance of a seemingly unusual finding when several outcomes or comparisons are examined. Some trials address this with a hierarchy of outcomes, an adjustment to statistical testing, or a plan to treat secondary results as exploratory. None of those approaches is described in the registry record, so the recalculated unadjusted p-values for secondary outcomes should not be treated as if they had been adjusted for the number of outcomes considered.

The record does not provide a detailed statistical analysis plan, nor does it list sponsor-reported analyses for the secondary outcomes. It is therefore not possible to assess whether the analyses followed a prespecified plan, whether alternative analyses were considered, or how any deviations were handled. The posted counts and recalculated contrasts remain interpretable as descriptive comparisons, but the absence of analysis-plan detail limits assessment of their inferential status.

Missing-data rules and the handling of participants with unavailable outcome measurements are not reported in the registry record. The posted outcome denominators are 22 and 24 for the primary endpoint and both secondary endpoints. These denominators match the arm sizes recorded for the outcomes, but the record does not explain whether all randomized participants had complete assessments, whether any imputation was used, or whether exclusions occurred before analysis. It would be inappropriate to infer a missing-data method from the matching denominators alone.

Analysis populations are also not defined. The registry record does not state whether results were analyzed by assigned group, among participants who received the allocated procedure, or using another population. It also does not describe protocol deviations or crossovers. Randomization supports a comparison according to assignment when analyzed appropriately, but the available record does not document the population rule used. These gaps affect interpretation of the results and prevent a full evaluation of the robustness of the analyses.

Finally, the registry record does not report interim analyses, stopping rules, or adjustments for interim monitoring. This is an absence of reporting, not evidence that such procedures were or were not used. Taken together, missing information about multiplicity, missing data, analysis populations, and analysis planning means that the posted numerical results should be read as limited summaries of the registered outcomes rather than a complete account of the trial’s statistical conduct.

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.

The registry record reports zero serious adverse events and zero other adverse events in both groups. The serious-event risk groups are 22 for Use of Ultrasound and 24 for No Ultrasound Used; the other-event risk groups are also 22 and 24, respectively. Deaths are recorded as zero in both groups. No serious-event terms are listed.

These figures describe the adverse-event counts posted in the registry record. They do not, on their own, establish that no adverse events occurred outside the categories or collection procedures reflected in the record. Definitions, ascertainment methods, follow-up duration for adverse events, and the process used to attribute events are not reported in the registry record. The primary outcome timeframe is 2 hours, but the safety follow-up timeframe is not specified in the adverse-event information.

Zero recorded events in a small group should be interpreted as an absence of events recorded in that group, not proof that an event is impossible or that there is no safety risk. The record does not provide enough detail to assess the completeness of safety monitoring or to compare uncommon events reliably. These counts are descriptive registry results and do not support medical advice or a broad safety conclusion.

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

The posted primary counts are close: 21 of 22 participants in the ultrasound arm and 23 of 24 in the palpation arm were recorded as having accurate epidural placement. The recalculated unadjusted risk difference is 0.004, with a 95% confidence interval from -0.114 to 0.122. This is a small point estimate with an interval that includes zero and extends in either direction. The data therefore do not provide a precise estimate of a difference, and the high unadjusted p-value does not establish that the methods are equivalent.

The trial addresses a focused procedural question, not every possible clinical consequence of the placement approach. The primary endpoint is not a direct measure of pain relief, the quality or symmetry of labor analgesia, catheter performance over time, or patient satisfaction. Although the investigators’ rationale connects accurate placement with these possible downstream outcomes, the posted results do not establish those outcomes. The registry record’s stated endpoint and its timeframe should guide interpretation.

The secondary outcomes add descriptive information about first-attempt success and success without angle adjustments. Their estimates remain uncertain, and the registry record does not report how multiplicity was handled. These outcomes are therefore not a basis for a definitive claim about the comparative performance of the techniques. The adverse-event record reports zero serious events, zero other events, and zero deaths in each group, but limited reporting detail and group sizes prevent a broad safety inference.

The findings apply most directly to the participants and procedures recorded in this trial. Important details—including eligibility criteria, the operational definition and assessment of accurate placement, analysis populations, missing-data handling, and the original design assumptions—are not reported in the registry record. The results cannot be assumed to apply unchanged to other clinical settings or patient groups. They also do not resolve whether a difference of a particular size would matter clinically, because no threshold for clinical importance is reported.

The most defensible reading is that the registry records very similar primary outcome counts in the two groups, while the unadjusted comparison remains imprecise. That description neither claims a treatment benefit nor rules one out. It distinguishes the observed data from stronger conclusions that would require clearer endpoint methods, a prespecified analysis account, and greater precision.

17. Why This Trial Matters Statistically

This trial is statistically instructive because its primary outcome counts are close, yet the comparison remains uncertain. A point estimate near zero can look reassuringly definitive when read alone. The interval shows why it is not: the data are compatible with a range of differences, including values in either direction. The distinction between a small observed contrast and a precise conclusion is central to interpreting randomized trial results.

The study also illustrates why outcome definitions matter. The rationale links midline placement with positive CSF, correct catheter placement, and adequate symmetrical analgesia, but the primary endpoint is the recorded count of accurate placement. Those concepts are related in the investigators’ stated hypothesis, yet they are not interchangeable outcomes. Clear operational definitions and assessment procedures are necessary to understand exactly what a count represents.

Another statistical lesson is that a high p-value does not prove equality. The registry record reports no equivalence or non-inferiority margin, and the primary interval is broad. Without a design and analysis framework intended to demonstrate equivalence, similar observed counts should not be translated into a claim that the techniques perform the same. The same caution applies to secondary comparisons, particularly when multiplicity handling is not reported.

Finally, the record demonstrates the importance of transparent reporting beyond outcome counts. Details about randomization implementation, masking of assessors, missing data, analysis populations, and the original sample-size rationale are not reported. Their absence does not invalidate the posted results, but it limits how fully readers can assess bias, precision, and the intended inferential claims. Statistical interpretation is strongest when numerical results and methods are both described.

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 specific to this trial affect interpretation. The registered primary endpoint is described as accurate epidural placement in the midline, but the precise operational definition, assessment method, and assessor are not reported in the registry record. This makes it difficult to judge how the outcome was determined or whether it could be assessed consistently across groups. The brief summary describes related intended consequences, including positive CSF, correct catheter placement, and adequate symmetrical analgesia or anesthesia, but the posted primary endpoint does not establish those consequences.

The group sizes are limited, and the primary risk-difference interval is broad. The point estimate is close to zero, but the data do not precisely locate the underlying difference. The registry record does not report an equivalence or non-inferiority design, a clinically important difference threshold, or the original sample-size justification. The sample-size illustrations based on the observed effect cannot fill those gaps or establish what the trial was designed to detect.

Methodological details are incomplete. Randomization is recorded, but sequence generation and allocation concealment are not described. The trial is listed as having no masking, while the masking status of outcome assessors is not reported. Participant eligibility, baseline characteristics, clinician experience, protocol deviations, and crossovers are also not described in the information available from the registry record.

Missing-data rules, analysis populations, multiplicity handling, and interim analysis procedures are not reported. The posted denominators match the recorded arm sizes, but that does not reveal how unavailable measurements or exclusions were handled. The record lists no reported analyses for the secondary outcomes, so the recalculated comparisons should be interpreted as unadjusted summaries rather than as a complete account of the trial’s planned analysis.

Finally, the adverse-event information provides event counts but not definitions, monitoring procedures, or a safety follow-up timeframe. Zero recorded events should not be generalized beyond the categories and period captured in the registry record. These limitations do not erase the recorded results, but they narrow the conclusions that can responsibly be drawn from them.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Does Ultrasound Help With Placement of Labor Analgesia in Pregnant Patients? — NCT02207972.
• Registry record last updated 2018-02-13; status last verified 2018-02.
• Results first posted 2018-02-13.
• 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

The registry record describes a completed, randomized, parallel trial with no masking, enrolling 46 participants. It compares ultrasound-guided CSE placement with placement using palpation of anatomical landmarks. The primary outcome is the number of participants with accurate epidural placement at 2 hours. The posted counts are 21 of 22 in the ultrasound arm and 23 of 24 in the palpation arm.

The recalculated unadjusted primary risk difference is 0.004, with a 95% confidence interval from -0.114 to 0.122 and an unadjusted p-value of 0.95. The interval indicates limited precision and includes zero. The secondary outcomes concern first-attempt success and success without angle adjustments in space; their recalculated comparisons are also unadjusted. The registry record reports zero serious adverse events, zero other adverse events, and zero deaths in each arm.

Important details about endpoint assessment, randomization procedures, analysis populations, missing data, multiplicity, and the original sample-size rationale are not reported in the registry record. The results therefore support a description of the posted counts and uncertainty, rather than a definitive claim of equivalence or a conclusion about downstream analgesia outcomes.