Gabapentin for Perioperative Pain Relief in Surgical Abortion: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gabapentin for Perioperative Pain Relief in Surgical Abortion (NCT04292171), a randomized early/phase 1 study. The primary outcome is Pain Score.

2. Clinical Question

3. Trial Design

The record describes a randomized, triple-masked, parallel-group clinical trial titled “Gabapentin for Perioperative Pain Relief in Surgical Abortion.” The sponsor is the University of Nevada, Las Vegas. The registry lists the phase as EARLY PHASE1 and the status as COMPLETED. Enrollment is recorded as 219.

The two interventions are gabapentin and placebo. The gabapentin arm is described as receiving 600 mg 1-2 hours before surgical abortion. The placebo arm is described as receiving placebo (vit C) at the same interval. The record does not specify who was masked under the triple-masking designation, or how masking was maintained.

The registry dates the start to 2017-05-01 and primary completion to 2018-03-30. The primary outcome is pain score at 5 minutes postoperative. Secondary outcomes listed include Pain Score 24, nausea, vomiting, and Pain Score at 30 Minutes Postoperative. Numerical summaries are present for nausea and vomiting at 24 hours postoperative; numerical values for the other listed secondary measures are not reported in the registry record.

The registry record does not report the randomization procedure, allocation concealment, eligibility criteria, recruitment setting beyond the office-based surgical abortion description, or the intended sample-size justification. It also does not report the analysis population definition or a detailed statistical analysis plan. These omissions limit what can be concluded about design decisions beyond the randomized, triple-masked, parallel-group structure recorded in the registry.

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:

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 Pain Score, measured over 5 minutes postoperative.

The primary endpoint is pain score at 5 minutes postoperative. It is described as a score on a 100mm visual analog scale (VAS) for level of pain, with scores from 1 to 100, where 1=no pain and 100= extreme pain. The outcome is summarized as a median with an inter-quartile range.

In general, a visual analog scale represents a participant’s subjective assessment along a bounded scale. A pain score can therefore capture the intensity of an experience that is not directly measured by an external instrument. The selected time point gives the score a specific interpretation: it concerns pain at 5 minutes after the procedure, not pain throughout recovery or at a later time. This outcome should not be treated as equivalent to the listed secondary pain measures at other time points.

The registry reports a median of 17.0 in the gabapentin arm and 17.0 in the placebo arm. The posted intervals are 0.0 to 60.0 for gabapentin and 2.0 to 53.0 for placebo. These are the reported group summaries, not confidence intervals for the medians. The record does not report a primary-endpoint test, confidence interval for an arm contrast, or the analysis population. Thus, the group summaries describe the observed distributions but do not establish the precision of an estimated treatment contrast.

The primary endpoint is a direct measure of the study’s stated pain question. Its usefulness for statistical interpretation depends not only on the scale, but also on the group comparison method and analysis details. Those details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry characterizes the study as randomized, triple-masked, and parallel-group. In a randomized trial, assignment is intended to reduce systematic differences between groups at baseline. Masking is intended to limit the influence of expectations on treatment delivery, outcome assessment, or reporting. These are general purposes of the design features; the registry record does not describe the randomization procedure, who was masked, or the safeguards used to maintain masking. The parallel-group label indicates that the listed arms are compared as separate groups rather than through a crossover design.

What does a median describe?

A median is the central value after observations are ordered. It is less affected by unusually high or low observations than an arithmetic mean, which can be useful when a score distribution is skewed. The inter-quartile range describes the middle portion of the observed values, from the lower quartile to the upper quartile. It describes spread within a group, not uncertainty about the group median and not the uncertainty of a difference between groups. Here, the primary results are reported as medians and inter-quartile ranges, but the record does not report a statistical method for comparing the medians.

The primary arm summaries are 17.0 in both groups. Their reported inter-quartile ranges differ in their endpoints. This is compatible with equal medians and different distributions; the median alone does not capture the full shape of the scores. A formal contrast could address a specified aspect of the distributions, but no such primary analysis is reported. A confidence interval for the difference would be needed to communicate the range of effect values compatible with that analysis, subject to its assumptions.

What does a confidence interval communicate?

In general, a confidence interval expresses uncertainty around an estimated quantity under a statistical procedure and its assumptions. It is not a range containing a fixed proportion of individual participants’ scores. For a difference in means, an interval that includes zero indicates that zero is among the values not ruled out by that interval at its stated confidence level; it does not prove there is no difference. The registry’s primary summaries are not accompanied by a confidence interval for an arm contrast. The secondary mean comparisons include recalculated 95% confidence intervals, derived from the posted summary statistics rather than reported as trial analyses.

For nausea, the recalculated mean difference is 0.0 and the 95% confidence interval is -3.303 to 3.303. For vomiting, the recalculated mean difference is 0.11 and the 95% confidence interval is -1.822 to 2.042. Both intervals include zero. The width of an interval depends on the observed variability, the amount of information, and the calculation method. A broad interval can be compatible with a range of effects in either direction, even when the point estimate is close to zero.

Why distinguish an unadjusted p-value?

A p-value summarizes how unusual data at least as incompatible with a specified null model would be, if that model and the test assumptions were correct. It is not the probability that the null hypothesis is true, nor a measure of clinical importance. The secondary p-values are labelled unadjusted because no correction for considering multiple outcomes is applied in these recalculations. If many outcomes are examined, the chance of at least one apparently notable result can increase. The registry record does not report a multiplicity procedure or a sponsor-reported analysis for these measures.

The posted nausea and vomiting comparisons use means and standard deviations, and the calculations are simple unadjusted recalculations from those summaries. The registry record does not report a distributional assessment or a model used by the trial investigators. General statistical practice treats conclusions from a mean-based method as dependent on its assumptions, including whether the mean and its standard error adequately characterize the data. The record does not permit a check of those assumptions using participant-level data.

How should the planning illustration be read?

The planning illustration is based on the observed vomiting effect, not on the trial’s own design justification. It assumes a two-sided significance level of 0.05, equal allocation, and a normal approximation. The effect to detect is expressed as a stated fraction of the observed effect. Under those assumptions, the illustration lists participants per arm for 80% and 90% power: planning for 100% of the observed effect gives 41,258 and 55,233; planning for 75% gives 73,348 and 98,192; planning for 50% gives 165,032 and 220,931.

These are planning illustrations, not observed power and not evidence that the trial was designed to detect those effects. They are highly dependent on the observed effect used as the starting point, which is small for this endpoint, and on the stated assumptions. The registry record does not report a trial-specific sample-size justification, target effect, or planned power calculation. The illustration should therefore be interpreted as a conditional design calculation rather than a statement about what the completed trial could reliably detect.

10. Multiplicity, Missing Data and Analysis Populations

The registry record does not report how multiplicity was handled. It lists a primary outcome and secondary outcomes at several times or for several symptoms, but there is no reported adjustment procedure, hierarchy of secondary hypotheses, or plan for interpreting multiple comparisons. In general, testing multiple outcomes can increase the chance of at least one apparently unusual result under null hypotheses. An adjustment or a prespecified hierarchy can address that issue, but the record does not establish whether either approach was used in the trial analysis.

The available nausea and vomiting p-values are unadjusted recalculations from posted summary statistics. They should not be read as multiplicity-controlled evidence. No reported analyses are listed for these secondary outcomes. The primary endpoint has no reported p-value or confidence interval, so there is no registry-reported primary inferential result to compare with the secondary calculations.

Missing-data handling is not reported in the registry record. The record gives the primary outcome denominators as 107.0 and 109.0, and the secondary denominators as 68.0 and 61.0 for nausea and vomiting. It does not explain why the denominators differ among outcomes, whether observations were missing, whether participants were excluded from particular analyses, or how any missing values were handled. No imputation method, sensitivity analysis, or reasons for missing outcome data are reported.

The analysis populations are also not reported in the registry record. It is therefore not possible to determine from the record whether analyses followed intention-to-treat principles, used a per-protocol population, or applied another rule. The total enrollment is recorded as 219, but enrollment alone does not identify which participants contributed to each outcome analysis. These uncertainties limit assessment of the robustness and generalizability of the posted comparisons.

11. 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 lists zero serious adverse events in the gabapentin arm among 107 participants at risk and zero in the placebo arm among 109 participants at risk. It also lists zero other adverse events in each arm, with the same respective numbers at risk, and zero deaths in both arms. No serious adverse event terms are listed.

These entries describe what the registry reports for the stated safety categories. A zero count in a record does not establish that an event is impossible or that the groups have identical safety profiles. The interpretation depends on how events were defined, collected, and followed, and those details are not reported in the registry record. The record also does not provide a safety analysis, confidence intervals, or a detailed account of ascertainment.

The listed counts should be read as recorded adverse-event summaries, not as a comprehensive account of every possible symptom or experience. The registry separately lists nausea and vomiting among secondary outcomes, but the adverse-event entries do not by themselves explain the relationship between those symptom measures and adverse-event reporting. The posted safety figures are descriptive and do not support a broader comparative safety conclusion.

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

The posted primary result describes the central pain scores at 5 minutes postoperative: both arms have a recorded median of 17.0. The associated inter-quartile ranges indicate the spread of scores within each arm, but they are not confidence intervals for a difference. Because the registry record does not report an inferential comparison for the primary outcome, the precision of the between-arm contrast cannot be determined from the primary summaries alone.

This result does not establish that the treatments produce identical pain-score distributions. Equal medians can coexist with differences in variability, distribution shape, or other features. Nor does it establish that one treatment changes pain more than the other. Such claims would require a clearly defined comparison, an appropriate analysis, and uncertainty estimates. The registry record does not provide those for the primary endpoint.

The secondary mean comparisons are recalculated, unadjusted results based on posted group summaries. Their confidence intervals include zero, but that fact is not proof of no difference. Their interpretation is limited by uncertainty, the lack of reported multiplicity handling, the absence of sponsor-reported analyses, and the fact that some listed secondary outcomes have no numerical results in the registry record. The planning calculations are conditional illustrations and are not observed power or evidence about the trial’s original design.

Randomization and masking are relevant design strengths as recorded, but they do not remove uncertainty created by incomplete reporting. The record does not give enough detail to assess analysis populations, missing-data handling, outcome ascertainment, or the primary statistical method. Accordingly, the posted data support a description of the recorded summaries and their limitations, not a definitive treatment-effect conclusion.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of the distinction between descriptive summaries and an inferential comparison. The primary outcome is reported with medians and inter-quartile ranges, but no formal contrast or uncertainty interval is reported. Readers can see the central values and within-group spread, yet cannot use those summaries alone to assess the precision of the between-arm difference.

The trial also illustrates why outcome-specific denominators and analysis populations matter. The registry records an enrollment of 219, while the numbers attached to outcome summaries vary. Without participant flow, analysis-population definitions, and missing-data details, readers cannot determine why the available denominators differ or how those differences affect interpretation. Transparent reporting of these features is important for evaluating whether a result could be sensitive to exclusions or missing observations.

Another statistical issue is the distinction between a trial’s own analysis and recalculations from summary statistics. The nausea and vomiting comparisons are recalculated and unadjusted, rather than listed as sponsor-reported analyses. Such calculations can offer context, but they do not replace a prespecified model or analysis plan. They also do not address multiplicity across the several outcomes listed in the record.

Finally, the planning illustration demonstrates how sample-size calculations depend on the effect chosen for detection and on assumptions such as allocation, significance level, and approximation method. It is not the trial’s design justification and not a measure of achieved power. The registry record does not report the original sample-size rationale. Together, these features make clear why complete statistical reporting is needed to move from outcome summaries to a well-calibrated interpretation.

14. 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 trial-specific reporting gaps limit interpretation. The registry record does not describe eligibility criteria or provide detailed characteristics of the population. The primary-outcome population field is empty, and the analysis populations are not reported. As a result, the extent to which the analyzed participants represent the enrolled population cannot be assessed from this record.

The primary endpoint is reported descriptively, without a reported between-arm test, confidence interval, or adjusted estimate. The group medians are equal as recorded, but no statistical method for comparing the primary distributions is given. The registry also does not explain the endpoint denominators or report participant flow and missing-data handling. These omissions prevent assessment of whether differences in available observations could affect the summaries.

The record contains no detailed protocol-level analysis plan, no multiplicity approach, and no sponsor-reported analyses for the two secondary measures with numerical results. The numerical secondary comparisons are unadjusted recalculations. Results for the listed secondary pain outcomes are not reported in the registry record, limiting assessment across time points.

Additional design and conduct details are not reported, including the randomization method, allocation concealment, masking procedures, outcome-assessment procedures, and the trial’s sample-size justification. The registry identifies the study as triple-masked but does not specify which roles were masked. The safety entries are counts without detailed definitions or ascertainment information. These limitations concern what can be evaluated from the registry record; they do not establish that the unreported procedures were absent from the trial.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Gabapentin for Perioperative Pain Relief in Surgical Abortion — NCT04292171.
• Registry record last updated 2020-12-02; status last verified 2020-11.
• Results first posted 2020-12-02.
• 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.

18. Record Summary

The registry record describes a completed, randomized, triple-masked, parallel-group trial of gabapentin versus placebo for perioperative pain in surgical abortion. The gabapentin arm received 600 mg 1-2 hours before the procedure, and the placebo is described as vitamin C given at the same interval. Enrollment is recorded as 219.

The primary outcome is pain score at 5 minutes postoperative on a 100mm visual analog scale. The recorded median is 17.0 in each arm, with inter-quartile ranges of 0.0 to 60.0 for gabapentin and 2.0 to 53.0 for placebo. A formal primary comparison is not reported in the registry record.

Nausea and vomiting at 24 hours postoperative have numerical summaries and unadjusted recalculated comparisons. Other listed secondary outcomes lack numerical results in the registry record. The record lists zero serious adverse events, zero other adverse events, and zero deaths in both arms, while detailed safety methods are not reported.