Postpartum Perineal Pain After Obstetric Anal Sphincter Injuries: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Postpartum Perineal Pain After Obstetric Anal Sphincter Injuries (NCT03470675), a randomized phase 4 study. The primary outcome is Perineal Pain in Postpartum Patients 1 Week After Obstetric Anal Sphincter Injuries..

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group, triple-masked, phase 4 trial. It lists an enrollment of 67 and a completed status. The study start is recorded as 2018-06-27, and primary completion as 2024-05-20. The registry identifies Northwestern University as the sponsor.

Three regimens were assigned: epidural saline plus intravenous saline; epidural morphine 3 mg plus intravenous saline; and epidural morphine 3 mg plus intravenous ketamine 0.3 mg/kg. The trial summary characterizes the saline regimen as placebo and the study as an assessment of acute pain following OASIS. The record labels the study triple-masked but does not state which groups of people were masked or describe how masking was maintained.

The primary endpoint is perineal pain one week after vaginal delivery, assessed using a verbal rating scale (VRS). The record identifies the summary parameter as a mean and the dispersion as an interquartile range. It also posts a group value and lower and upper values for each arm, but does not explain what those lower and upper values represent. The number of participants included in the posted primary outcome summaries differs across arms. The registry lists losses to follow-up in the endpoint description, but does not explain how missing outcomes were handled.

The record lists 22 outcome measures and 21 posted secondary outcomes. The secondary outcome names include perineal pain, maternal-infant bonding, postpartum depression, and current pain measured with the Brief Pain Inventory short form. The registry reports no analysis entries for the trial. Details such as the randomization procedure, allocation concealment, masking roles, analysis population, and prespecified statistical model 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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Epidural saline + IV saline group 1 lost to follow up Epidural Morphine 3 mg + saline group 7 lost to follow up Epidural Morphine 3 mg + ketamine .3 mg/kg 1 lost to follow up

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 Perineal Pain in Postpartum Patients 1 Week After Obstetric Anal Sphincter Injuries., measured over 1 week after vaginal delivery.

The primary endpoint is a perineal pain score one week after vaginal delivery among postpartum patients with an obstetric anal sphincter injury. It uses a verbal rating scale scored from 0 for no pain to 10 for the highest pain. Because the scale runs from no pain to more pain, lower scores indicate less reported pain on the scale; they do not, by themselves, establish a difference between treatment groups.

A pain score is a way to record the reported intensity of pain at a specified time. Here, the endpoint focuses on a particular early postpartum time point rather than describing pain over the whole recovery period. The study summary frames the objective as assessing the incidence of perineal pain, while the registered primary measure is a score. The registry does not report a threshold that classifies a score as pain present or absent, so the endpoint should be read as a scale-based measure rather than a reported count of patients with pain.

The record labels the summary parameter as a mean and the dispersion as an interquartile range. It posts one value and two accompanying bounds for each arm, but does not identify the meaning of those bounds. Consequently, the bounds cannot be interpreted as confidence intervals or as the endpoints of the interquartile range from the record alone. The registry does not report a prespecified clinically important difference for this scale.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Randomized, parallel-group design means that participants are allocated to one of several regimens and followed in their assigned group. In general, randomization is used to reduce systematic differences between groups at enrollment. It does not guarantee that every characteristic will be balanced, especially in a limited sample, and it cannot resolve missing outcome data. The registry identifies the design as randomized and parallel, but does not report the sequence-generation method, allocation concealment procedure, or baseline characteristics needed to examine how these design features operated.

What does triple masking tell the reader?

The registry labels the trial triple-masked. In general, masking can reduce the influence of knowledge about treatment assignment on care, participant reports, and outcome assessment. The endpoint is a participant-reported pain score, so awareness of assignment could be relevant to how a report is made. However, the record does not specify which parties were masked, what information was concealed, or whether masking was assessed. The label alone does not establish that masking was successful.

How should the pain scale be read?

The VRS runs from 0, no pain, to 10, the highest pain. It is a bounded scale: its values have a defined lower and upper limit. The registry says that the group summary parameter is a mean. A mean describes the average score in a group, while an interquartile range, in general, describes the middle half of a distribution. These summaries answer different questions: one describes the average level, and the other describes the spread of individual scores around the distribution's center. The posted endpoint information identifies both a mean and an interquartile range, but does not unambiguously identify the role of each posted lower and upper value.

In general, a confidence interval describes uncertainty around an estimated quantity under a statistical model and analysis procedure. Its interpretation depends on what quantity it covers and how it was calculated. The registry does not label the lower and upper values accompanying the group summaries, so they cannot be treated as confidence intervals. Nor can their width be used to compare precision unless their definition is known. The record likewise does not provide a standard deviation or another clearly identified measure of variability.

What would a treatment contrast add?

A group summary describes outcomes within an arm. A treatment contrast estimates how outcomes differ between arms, and an inferential analysis can quantify uncertainty around that contrast. In general, a confidence interval for a contrast can indicate which effect sizes remain compatible with the observed data and the analysis assumptions. A p-value, when used, addresses compatibility with a specified null hypothesis under a statistical model; it does not measure the probability that a treatment works. The registry contains no posted group contrast, confidence interval, test statistic, or p-value. None should be reconstructed from the group summaries alone for interpretation.

In general, standard statistical procedures for means rely on assumptions about the outcome distribution and sampling process. Pain scores are bounded and can have distributions that are not well represented by a normal model. Alternative approaches may be appropriate depending on the study question and data structure, but the registry does not state which model or test was used. A description of a possible method would not establish that the trial used it.

Why does dispersion matter?

In general, over-dispersion means that observed variation is greater than a model expects. When a model assumes less variation than the data contain, standard errors can be too small and uncertainty can be understated. This is a general consideration rather than a reported finding about this trial: the registry does not provide enough distributional information to determine whether over-dispersion was assessed or present. For this endpoint, knowing how the lower and upper values were defined and how individual VRS scores were distributed would help characterize variability.

The study has three arms, so its overall statistical question could involve more than one pairwise contrast. In general, if several hypotheses are tested, a multiplicity strategy can address the increased chance of false-positive findings across tests. Options and their consequences depend on which comparisons were prespecified and which outcomes were considered primary. The registry does not report a testing hierarchy, multiplicity adjustment, or primary contrast. It is therefore not possible to infer how any family of comparisons was handled.

The sample-size assumptions recorded for a planning illustration use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is defined as a fraction of an observed effect. This describes an illustrative planning approach, not the trial's original design or a result about the observed sample. The registry does not report the trial's own sample-size justification or a planned target for power. Planning illustrations are not observed power and do not replace a prespecified design rationale.

Finally, the registry reports zero analysis entries. That absence means the statistical plan, fitted models, analysis populations, and inferential results are not documented in the registry record. General explanations of statistical concepts cannot fill those gaps or establish which methods were actually used.

10. Multiplicity, Missing Data and Analysis Populations

The trial has three assigned regimens and the registry lists 22 outcome measures, including 21 posted secondary outcomes. In general, examining several outcomes or treatment contrasts creates a multiplicity issue: the chance of at least one apparently notable result can increase as the number of tests increases. A prespecified hierarchy, adjustment procedure, or other strategy can clarify how multiple findings are interpreted. The registry does not report such a strategy, nor does it identify a planned primary contrast among the three arms.

The record reports no analysis entries. It therefore does not describe the statistical analysis plan, analysis populations, treatment of protocol deviations, or whether results were analyzed according to assigned group. The registry also does not report an interim analysis plan. These omissions mean that the results cannot be assessed against a documented prespecified inferential approach.

The primary endpoint description lists losses to follow-up of 1 in the epidural saline plus intravenous saline group, 7 in the epidural morphine plus intravenous saline group, and 1 in the epidural morphine plus intravenous ketamine group. The posted primary outcome summaries include 13, 19, and 24 participants, respectively. The registry does not explain how the loss counts relate to these outcome counts, whether any other exclusions occurred, or whether missing values were imputed. It also does not report reasons for loss to follow-up or compare participants with and without observed scores.

In general, missingness can matter when the probability of having an outcome recorded is related to the outcome itself or to participant characteristics. Analyses that rely only on observed scores may be affected if missingness is informative. This is a general statistical concern, not a claim about what happened in this trial. Without a stated missing-data method or sensitivity analysis, the effect of missing pain scores on the posted summaries is not established.

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.

Most frequent non-serious adverse event terms

The registry reports serious adverse event counts of 0 in each group: among 14 at risk in the epidural saline plus intravenous saline group, among 26 at risk in the epidural morphine 3 mg plus intravenous saline group, and among 25 at risk in the epidural morphine 3 mg plus intravenous ketamine 0.3 mg/kg group. Deaths are reported as 0 in each group. These are the serious-event and death counts entered in the registry; they do not establish that no events occurred outside the registry's recorded categories or reporting period.

The registry separately reports other adverse event counts of 4 among 14 at risk for the saline group, 14 among 26 at risk for morphine plus saline, and 13 among 25 at risk for morphine plus ketamine. These are counts of affected participants as recorded, not a measure of event severity or a comparison adjusted for follow-up and exposure. The record does not provide event descriptions in the listed serious-event terms, and no serious-event terms are listed.

In general, safety counts are best interpreted alongside definitions, observation periods, event types, and the completeness of reporting. The registry does not provide enough detail to determine whether the groups had comparable safety surveillance or whether the counts refer to unique participants experiencing at least one event. No causal conclusion about the regimens follows from these counts alone.

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

The posted results establish that the registry contains group-level VRS summaries for perineal pain one week after vaginal delivery and gives the number of participants included in each summary. The reported values are 3.5 for epidural saline plus intravenous saline, 2.7 for epidural morphine 3 mg plus intravenous saline, and 2.4 for epidural morphine 3 mg plus intravenous ketamine 0.3 mg/kg. On the scale described in the record, lower values correspond to lower reported pain scores. This is a description of the posted summaries, not an estimate of a treatment effect.

The record does not report direct statistical comparisons, uncertainty intervals for between-group effects, or p-values. The lower and upper values next to the group summaries are not defined in the record, so they cannot resolve the uncertainty around differences between regimens. A numeric ordering of group summaries does not show whether the groups differ beyond sampling variation, nor whether any difference would be clinically important.

The registry also does not report a threshold for classifying pain as present, despite describing the study objective in terms of incidence. The endpoint is therefore most clearly understood as a score at a specified time point. The summaries do not describe the entire postpartum course, pain at other time points, or outcomes such as maternal-infant bonding or postpartum depression.

In general, a treatment conclusion requires a clearly defined comparison, a suitable analysis, and an assessment of uncertainty and potential bias. Randomization is a useful design feature, but it does not substitute for those results. The absence of posted analysis entries, missing-outcome methods, and a documented multiplicity strategy limits what can be concluded from the registry record. The record does not establish that one regimen is superior, equivalent, or inferior to another.

The adverse-event entries provide counts of serious and other adverse events and deaths as recorded. They do not on their own establish comparative safety. Taken together, the posted material describes the trial design and some observed outcome and safety summaries, but leaves the inferential questions unanswered.

13. Why This Trial Matters Statistically

This trial addresses a clearly specified measurement problem: perineal pain after OASIS at one week following vaginal delivery. The use of a bounded verbal rating scale provides a direct, patient-reported score at a defined time point. The registry also identifies three distinct medication regimens, allowing a study design that includes a saline comparator and two active regimens.

Statistically, however, describing the outcome is not the same as estimating a treatment effect. Group summaries can show the observed score levels among participants with recorded outcomes, but a comparative conclusion requires a defined contrast and an account of its uncertainty. The registry's lack of posted analysis entries makes this distinction especially important. Readers should not infer a confirmatory result solely from the numerical order of the three summaries.

The study also illustrates why endpoint definitions and reporting details matter. The objective refers to incidence, while the primary endpoint is recorded as a score; the endpoint description identifies a mean and interquartile range, but the posted lower and upper values are not defined. The distinction between an individual-level pain score, a group summary, a binary incidence outcome, and a between-group treatment effect is consequential for interpretation.

Finally, the reported losses to follow-up, three-arm design, and multiple listed outcomes make analysis documentation important. Missing-data handling and multiplicity decisions can affect the meaning of inferential results. Because these details are not reported in the registry record, the posted information is useful for understanding the trial's scope and descriptive results, while remaining insufficient to answer whether the regimens differed statistically or clinically.

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.

The registry record does not report a statistical analysis plan, a planned primary comparison, a statistical test, or an estimated contrast among the three groups. It also does not report confidence intervals for treatment effects or p-values. As a result, the posted group summaries cannot establish the magnitude or precision of a comparative effect.

The meaning of the lower and upper values accompanying each primary outcome summary is not identified. The endpoint fields describe the summary as a mean with interquartile range, but do not clearly explain how those labels relate to every displayed value. Without that clarification, those values should not be treated as confidence intervals or as a specified measure of distributional spread.

The endpoint description records losses to follow-up of 1, 7, and 1 across the respective groups, but does not explain how missing scores were handled or how those counts relate to the reported outcome sample sizes. Reasons for missingness, imputation, sensitivity analyses, and the analysis population are not reported in the registry record. The extent to which missing outcomes could affect the summaries is therefore unknown.

The record identifies the trial as randomized and triple-masked but does not describe the randomization procedure, allocation concealment, which parties were masked, or whether masking was successful. It does not report baseline characteristics that would help readers assess comparability of the observed groups. The original sample-size justification and any interim analysis plan are also not reported.

The registry lists multiple outcomes but does not describe a multiplicity strategy. It does not give an operational threshold for classifying the pain score as incidence of pain, and does not define the posted bounds. These reporting gaps limit interpretation of both the endpoint and the broader outcome set. These are limitations of what can be established from the registry record; they do not establish that a particular method was or was not used outside that record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Postpartum Perineal Pain After Obstetric Anal Sphincter Injuries — NCT03470675.
• Registry record last updated 2026-04-24; status last verified 2026-04.
• Results first posted 2026-04-24.
• 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

NCT03470675 is a completed, randomized, parallel-group, triple-masked phase 4 trial sponsored by Northwestern University. The registry records enrollment of 67. It compares epidural saline plus intravenous saline, epidural morphine 3 mg plus intravenous saline, and epidural morphine 3 mg plus intravenous ketamine 0.3 mg/kg.

The primary outcome is perineal pain one week after vaginal delivery, measured on a VRS from 0 for no pain to 10 for the highest pain. The posted group summaries are 3.5, 2.7, and 2.4, with outcome sample sizes of 13, 19, and 24, respectively. The registry also reports loss-to-follow-up counts and adverse-event counts.

No statistical analysis entries are reported. The record does not explain the lower and upper values accompanying the pain summaries, provide a treatment-effect comparison, describe missing-data handling, or state a multiplicity approach. The posted information supports a description of the trial and its group summaries, but does not provide an inferential comparison of the regimens.