IV Acetaminophen vs IV Morphine for Pain Control in Pregnant Women: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for IV Acetaminophen vs IV Morphine for Pain Control in Pregnant Women (NCT02267772), a randomized na study. The primary outcome is Change in Pain Intensity as Assessed by a Visual Analogue Scale (VAS).

2. Clinical Question

3. Trial Design

The registry describes a randomized, controlled, parallel-group trial comparing IV acetaminophen with IV morphine for pain control in pregnant women. Random allocation means participants were assigned to one of the two treatment groups rather than choosing their group. The record does not report how the random sequence was generated, whether allocation was concealed before assignment, or whether randomization was stratified. Those details are not reported in the registry record and should not be inferred from the word randomized alone.

The trial was unmasked. Participants and clinical staff therefore were not described as blinded to the assigned medication. The registry summary says participants would complete a pain scale after medication administration and be asked about side effects. Because pain scores and satisfaction are reported by participants, knowledge of the treatment assignment could be relevant when interpreting those outcomes. The record does not describe measures intended to reduce that potential influence.

The enrollment recorded in the registry is 163. This is the recorded enrollment figure, not a report of how many participants contributed data to each outcome. The primary-outcome population counts show smaller, differing numbers of observations across treatment groups and labor settings. The record does not explain why some participants did not contribute primary-outcome data, nor does it state how missing observations were handled.

The registry lists the trial status as terminated and gives the primary completion date as 2019-04-27. The reason for termination, whether recruitment ended as planned, and whether the trial reached its intended enrollment are not reported in the registry record. The record describes a comparative effectiveness objective and names maternal and fetal adverse effects among the aims, but it does not report a protocol-level sample-size justification or detailed analysis plan.

The interventions are described as IV acetaminophen and IV morphine. The summary gives maximum numbers of standard doses during the hospital stay, but not dose amounts. It also describes rescue medication as an outcome, without specifying in the available record how rescue treatment was selected or administered. The design can therefore be characterized at the broad level of a randomized, open-label, two-arm comparison, while several operational details remain unreported.

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: 163 were enrolled, including those in Group 1 (Pregnant women with uterine contractions, but not in labor), Group 2 (Pregnant women with uterine contractions in the first stage of labor), and Group 3 (Pregnant women with a medical condition associated with pain). The participant flow only reflects participants enrolled in Group 1 and Group 2, and not those in Group 3.

Overall Study

Analysis population for the primary outcome, as defined in the registry: For the IV Acetaminophen arm, data were collected for 24 out of 30 participants in pre-labor and 18 out of 18 participants in the 1st stage of labor. For the IV morphine arm, data were collected for 30 out of 32 participants in pre-labor and 20 out of 20 participants in the 1st stage of labor.

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 Change in Pain Intensity as Assessed by a Visual Analogue Scale (VAS), measured over baseline, 120 minutes after administration.

The primary endpoint is change in pain intensity assessed with a visual analogue scale. The registry describes a scale ranging from 0mm to 140mm, on which a participant marks pain with a pen. Measurements were intended at baseline and 120 minutes after administration. A change score aims to represent how pain ratings shifted from each participant’s starting value, rather than relying only on a single rating after treatment.

The registry’s endpoint description states that negative differences indicate a pain score worse than baseline and positive differences indicate improvement from baseline. That stated direction is important when interpreting any reported estimate: the sign is meaningful only in relation to the registry’s definition. The record does not provide the group means, standard deviations, between-group contrast, or uncertainty interval for this outcome. Consequently, the direction or size of the observed changes cannot be established from the registry record.

Using a continuous pain scale can retain more gradation than reducing responses to categories such as improved or not improved. A group mean describes the average score or change, while a standard deviation describes variation among observations around that mean. Those are general statistical interpretations; they do not establish whether a measured change is important to participants. The registry record does not state a threshold for a clinically meaningful change or provide a separate minimal important difference.

Differences in the number of recorded observations across labor settings and treatment groups matter to the endpoint’s interpretation. A comparison is most informative when the analysis population, timing, and handling of missing measurements are clear. Those analysis details and the numerical primary results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Random allocation and the comparison

General statistical explanation: random allocation is intended to make treatment groups comparable, on average, with respect to factors that could influence outcomes. It does not guarantee that every characteristic will be balanced in a particular trial. In a parallel-group trial, each participant is assigned to one group and outcomes are compared between groups. The registry identifies randomization and a parallel model, but the sequence-generation method and allocation-concealment procedures are not reported in the registry record. Those omissions limit the detail available for judging how assignment was implemented.

The trial was unmasked. General statistical explanation: when participants know which treatment they receive, expectations may affect subjective reports, and staff knowledge may influence care or outcome assessment. A participant-marked pain scale is a subjective measurement, so masking status is relevant context. It does not, by itself, show that a result is biased; it identifies a possible source of influence that should be considered alongside the actual analysis. The record does not describe procedures to assess or reduce such influence.

What does a mean and standard deviation describe?

The primary endpoint is continuous and the registry identifies the mean and standard deviation as its summary form. General statistical explanation: a mean is an average, while a standard deviation describes how spread out individual observations are around that average. A mean change can give a concise summary of the group’s average score shift, but it does not show the full distribution of responses. The standard deviation is not the same as the uncertainty around the mean or the uncertainty around a treatment contrast. The registry does not report the primary outcome values needed to interpret these summaries.

A treatment comparison might be expressed as a difference between group means, with an uncertainty interval. General statistical explanation: a confidence interval gives a range of estimates compatible with the data and the specified statistical procedure; it conveys precision as well as the estimated direction and size. A p-value addresses compatibility with a specified null model, but does not quantify clinical importance or the probability that a treatment is effective. Neither a confidence interval nor a p-value for the primary outcome is reported in the registry record, so no such interpretation is possible for this trial’s posted primary results.

Why does the scale and its direction matter?

The VAS ranges from 0mm to 140mm, and the registry describes ratings at baseline and 120 minutes after administration. General statistical explanation: a change score depends on the order in which the measurements are subtracted and on the stated sign convention. Here the registry defines negative differences as worse than baseline and positive differences as improvement. The same numerical change would be misread if a reader assumed a different convention. The registry does not report actual change values, so the sign convention can be described but not applied to a trial result.

Continuous outcomes can be analyzed in different ways, including comparing change scores or adjusting a follow-up comparison for baseline values. These approaches can differ in assumptions and precision. Which approach was used, whether any covariates were included, and how repeated or setting-specific observations were handled are not reported in the registry record. No method should be attributed to the trial without that information.

What role do missing observations play?

The number of participants with primary-outcome data differs by treatment group and labor setting. General statistical explanation: missing outcome data can reduce precision, and it can also bias a comparison if the likelihood of having a recorded result is related to the outcome or treatment. The amount and pattern of missingness alone do not reveal whether bias occurred. Interpretation depends on why values are missing and on the assumptions and methods used to address them. Reasons for missing primary measurements, an analysis population definition, and a missing-data method are not reported in the registry record.

The enrollment figure is not interchangeable with the number of observations analyzed for a particular endpoint. General statistical explanation: an analysis population may include all randomized participants, participants who received treatment, or those with observed measurements, depending on a prespecified plan. Each choice answers a somewhat different question. The registry record does not identify which population was used for the primary comparison.

How should planning illustrations be read?

The sample-size assumptions describe planning illustrations based on a stated fraction of the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. General statistical explanation: such illustrations ask how many participants per arm would be required under specified assumptions to detect a target effect with a chosen power. They are conditional planning calculations, not evidence that the trial had that power and not a measure of the probability that a result is true. The record does not report a protocol sample-size justification, and the illustrations should not be read as the trial’s own design rationale or as observed power.

For continuous outcomes, planning calculations depend on the assumed effect and variability, among other assumptions. If the target effect is expressed as a fraction of an observed effect, the illustration inherits uncertainty in that observed estimate. The primary numerical results are not reported in the registry record, so the clinical interpretation of any such planning illustration cannot be independently connected to a reported primary estimate. No planning illustration can replace an effect estimate with its uncertainty.

The registry lists multiple outcomes, but does not report how the analyses were conducted or how inference across outcomes was handled. General statistical explanation: analysis choices, assumptions, and multiplicity procedures affect how results should be interpreted. The record does not report whether interim analyses occurred, the prespecified testing hierarchy, or adjustments for multiple comparisons. These details should remain unknown rather than being inferred from the trial design or outcome list.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome and several secondary outcomes, including pain relief, rescue medication use, study-drug quantity, satisfaction, maternal side effects, and fetal heart-rate changes. Considering multiple outcomes can raise a multiplicity issue: general statistical explanation, when many hypotheses are tested, the chance of at least one apparently unusual result can increase if each is judged separately using the same threshold. Approaches such as prespecifying a primary comparison, controlling a family-wise error rate, or treating secondary results as exploratory can address different goals. The registry record does not report a multiplicity strategy, hierarchy among secondary outcomes, or analysis plan, so none should be assumed.

The record lists no analyses in the analysis count and does not provide numerical primary-outcome results. This means the registry information does not support a reconstruction of the testing process or the selection of reported results. Whether analyses were performed but not entered, or were not conducted, is not reported in the registry record.

Primary-outcome data are recorded for different numbers of participants across the two treatment groups and labor settings. Reasons for missing data, the handling of missing observations, and the population included in any analysis are not reported in the registry record. General statistical explanation: these details matter because an analysis restricted to participants with recorded outcomes can be misleading if missingness is related to treatment or pain response. The counts alone cannot establish the direction or magnitude of any such effect.

The record also does not report interim analyses, stopping rules, or whether the primary outcome and analysis methods were changed. The trial status is listed as terminated, but the reason and its relationship, if any, to the analyses are not reported. These unknowns limit assessment of selective reporting and the completeness of the outcome record.

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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: adverse reaction to demerol administered as rescue medication, which required narcan for reversal (2.1%).

The registry reports serious adverse-event counts separately by treatment group. In the IV acetaminophen group, 1 of 48 participants at risk was recorded as affected; in the IV morphine group, 0 of 52 was recorded as affected. The registry lists zero deaths in both groups. These figures are counts in the registry record and should not be treated as a statistical comparison or as proof that an event can or cannot occur.

For other adverse events, the record lists 21 of 43 participants at risk in the IV acetaminophen group and 15 of 51 in the IV morphine group. These are distinct from the serious adverse-event counts and use their own reported at-risk denominators. The registry also lists the serious-event term “Adverse reaction to demerol administered as rescue medication, which required narcan for reversal” with 2.1%. The record does not clarify the relationship of this term to the group-level counts in the information available for interpretation.

General statistical explanation: adverse-event counts are descriptive unless accompanied by clearly defined event ascertainment, follow-up, denominators, and a comparative analysis. The record does not report detailed event definitions, timing, severity grading, or an inferential comparison. The reported counts therefore describe what the registry lists, but cannot establish a causal difference in safety between the treatments.

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

The registry record establishes that a randomized, open-label comparison of IV acetaminophen and IV morphine was planned and conducted for pain management in pregnant women. It identifies a primary pain-intensity outcome, describes its scale and assessment timing, and lists secondary outcomes related to pain, rescue medication, satisfaction, and maternal and fetal events. Those details define the clinical question, but they are not themselves evidence of comparative benefit or harm.

The numerical primary-outcome findings are not reported in the registry record. As a result, the record does not show how pain scores changed in either group, whether the groups differed, or how precisely a difference was estimated. The stated direction of the VAS change provides a key for interpreting a result if one is reported, but it cannot substitute for the missing values. The secondary-outcome names likewise do not establish what happened for those outcomes.

Safety counts are available, including serious adverse events, other adverse events, and deaths. These are descriptive figures. Without further information on event definitions, timing, follow-up, and comparative analyses, they do not establish that one treatment caused more or fewer events than the other. A recorded count of zero is not evidence that risk is absent.

General statistical explanation: a well-interpreted trial result needs an estimate, a measure of uncertainty, and enough information about design and analysis to assess the credibility and scope of that estimate. Randomization is an important design feature, but it does not fill gaps in outcome reporting, missing-data handling, or analysis methods. The registry record’s termination status also does not explain why the trial ended or what conclusions were reached.

Accordingly, the record supports a description of the study question and some reported safety counts, but not a conclusion about the relative pain outcomes of IV acetaminophen and IV morphine. It also does not establish whether either approach reduced opioid use or affected maternal or fetal outcomes, despite those aims appearing in the trial summary. Those conclusions require results and analyses that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically noteworthy because its primary outcome is a participant-reported, continuous measure, while the registry also describes several clinically relevant secondary outcomes. That combination illustrates why a clear outcome hierarchy and analysis plan matter. A single primary endpoint can focus the main comparison, while secondary endpoints can add context; without reported methods and results, however, readers cannot determine how the trial translated these aims into statistical conclusions.

The design also brings together randomization and open-label treatment. General statistical explanation: randomization is intended to reduce confounding in treatment comparisons, while lack of masking can matter especially for subjective outcomes and treatment-related decisions. These are separate design features. Neither one cancels out the other, and their importance depends on how the outcome was collected and analyzed. The registry identifies both the randomized allocation and the lack of masking but does not give enough procedural detail for a fuller assessment.

Unequal numbers of recorded primary-outcome observations across groups and labor settings make analysis populations and missing-data handling especially important to understand. General statistical explanation: a reader needs to know which participants contribute to the estimate and whether missingness could be related to outcomes. The registry lists endpoint-specific counts but does not report the reasons for missing values or the method used to handle them.

The entry also illustrates the distinction between planning calculations and evidence from an observed treatment comparison. Sample-size planning illustrations rely on assumptions; they are not proof of actual power or of an effect. Likewise, adverse-event counts provide descriptive information but do not replace comparative estimates with uncertainty. These distinctions are important when a registry record contains a trial’s aims and design but lacks numerical primary results and a detailed analysis account.

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 principal limitation of the registry information is that it does not report numerical results for the primary VAS outcome. Group summaries, a treatment contrast, uncertainty intervals, and a p-value are not reported in the registry record. Without these, the central comparison cannot be evaluated for magnitude, direction, or precision. The secondary outcomes are named, but their numerical findings are also not reported in the information.

The primary-outcome counts differ across treatment groups and labor settings. The registry does not explain why some participants lack recorded data, whether data from pre-labor and the first stage of labor were analyzed separately or combined, or how repeated assessments were handled. It also does not identify the analysis population or report a missing-data method. These are trial-specific gaps, not evidence that a particular bias occurred.

The study is described as unmasked, while the primary outcome is based on participants’ pain ratings. This is relevant context for a subjective endpoint, but the registry does not describe the exact assessment procedures or steps to limit potential influence from treatment knowledge. The randomization method and allocation concealment are also not reported.

Although the record lists multiple secondary outcomes and safety counts, it does not give a statistical analysis plan, multiplicity approach, event definitions, or detailed event-level reporting. The listed termination status and primary completion date do not explain why the trial ended. A protocol-level sample-size justification, interim-analysis details, and any changes to planned outcomes or methods are not reported in the registry record. These omissions restrict assessment of design implementation, completeness, and comparative interpretation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: IV Acetaminophen vs IV Morphine for Pain Control in Pregnant Women — NCT02267772.
• Registry record last updated 2021-01-22; status last verified 2020-12.
• Results first posted 2021-01-22.
• 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 NCT02267772, a randomized, open-label, parallel-group comparison of IV acetaminophen and IV morphine for pain management in pregnant women. Enrollment is recorded as 163, and the status is listed as terminated, with primary completion on 2019-04-27.

The primary outcome is change in VAS pain intensity, measured at baseline and 120 minutes after administration. The scale is described as 0mm to 140mm, with positive differences indicating improvement and negative differences indicating worse pain than baseline. The registry reports differing numbers of primary-outcome observations by treatment group and labor setting, but does not report numerical primary results or the analysis method.

Secondary outcomes include pain relief, rescue medication, total study-drug amount, satisfaction, maternal side effects, and fetal heart-rate changes. Serious and other adverse-event counts are listed, as are zero deaths in each group. The reason for termination, detailed analysis plan, handling of missing data, and comparative outcome estimates are not reported in the registry record.