Comparison of Nifedipine Versus Indomethacin for Acute Preterm Labor: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Nifedipine Versus Indomethacin for Acute Preterm Labor (NCT03129945), a randomized na study. The primary outcome is Number of Participants With Delay of Preterm Delivery by 48 Hours..

2. Clinical Question

This is a direct comparison of two active medications, rather than a comparison with placebo or no treatment. The registry summary describes the study purpose as determining which medication best delays preterm labor and identifies delay of delivery for 48 hours as the primary outcome. It also states that the two medications were commonly used at the institution and that direct comparisons had been limited. These statements describe the study rationale; they do not establish what the results mean for care.

The registry lists 36 participants as enrolled. It does not report participant-level characteristics, such as gestational age distribution, baseline clinical status, or other factors that might help readers understand how closely the participants resemble a particular clinical population. The summary also refers to 450 participants being asked to participate across all study sites. The record does not explain the relationship between that planned recruitment statement and the enrollment of 36 recorded in the study information.

3. Trial Design

The study is listed as randomized, with a parallel-group model and no masking. The two arms are nifedipine and indomethacin, and both medications are described as oral. A parallel design assigns participants to one treatment arm and follows those groups over the study period; random allocation is intended to make treatment groups comparable on average. The record does not describe how the random sequence was generated, whether allocation was concealed, or how randomization was implemented.

No masking is reported. In an unmasked study, participants and study personnel may know which treatment has been assigned. The registry does not say whether the person determining the primary outcome was masked, nor does it give further detail about steps taken to limit the influence of treatment knowledge on assessment. The extent to which knowledge of treatment could influence this particular outcome depends on how the outcome was defined and ascertained, details that are not reported in the registry record.

The registry lists enrollment of 36 and reports 15 participants in the nifedipine arm and 21 in the indomethacin arm. The study status is completed. The recorded start date is 2017-01-17 and the primary completion date is 2019-04-18. The phase is listed as NA. The stated outcome follow-up is for the duration of the hospital stay, with an expected average of 1 week. That is a stated expectation, not a participant-level description of actual follow-up time.

The registry does not report a trial-specific sample-size justification, planned allocation ratio, recruitment targets by arm, or the reasons for the observed arm sizes. It gives no information about interim analyses, stopping rules, protocol amendments, or deviations from the planned design. Although the summary mentions a larger number of participants to be asked across study sites, the record does not explain whether that figure was a target, how it related to this enrollment, or whether recruitment was conducted as planned.

These design details matter when interpreting a randomized comparison. Randomization is a design feature, not a guarantee that every source of bias or uncertainty has been addressed. The absence of masking and the lack of reported allocation and outcome-assessment procedures leave important aspects of implementation unclear. The registry does not report whether the analysis followed the original randomized assignments or how participants with incomplete records were handled.

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

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 Delay of Preterm Delivery by 48 Hours., measured over Participants will be followed for the duration of the hospital stay, an expected average of 1 week.

The primary endpoint is the number of participants with delay of preterm delivery by 48 hours. The outcome description places the question in women diagnosed with threatened preterm labor prior to 32 weeks of gestational age and treated with either nifedipine or indomethacin. The registry states that participants would be followed for the duration of the hospital stay, with an expected average of 1 week.

This is a binary participant-level outcome: for each participant, the event is whether the specified delay was achieved or not. Counting participants with the event offers a direct way to compare the share of each treatment group meeting the defined outcome. A delay threshold can be useful in clinical research when investigators want to distinguish whether an event occurred within a prespecified period, although the registry does not give the protocol rationale for selecting this threshold.

The outcome is described as delay of delivery, but the record does not specify exactly how the timing was determined, what event marked the start of the interval, or how cases without an observed delivery during follow-up were classified. It does not report whether outcome assessment was based on clinical records, participant report, or another process. Those operational details are important because different definitions or measurement procedures can affect whether participants are counted as having the event.

The outcome should therefore be read as the registry’s stated count endpoint, not as a complete account of pregnancy duration or all outcomes relevant to participants. The registry lists one outcome measure and no secondary outcomes. It does not report additional clinical measures that could clarify the broader consequences of treatment or the course of the hospital stay.

7. Results Posted in the Registry

• Indomethacin: 100.0% (21/21) versus 100.0% (15/15) on control; risk difference 0.0 percentage points (95% CI 0.0 to 0.0), risk ratio 1.00 (1.00–1.00); unadjusted two-proportion z-test p = n/a.

8. Statistical Interpretation

9. Statistical Methods Explained

What does the event count represent?

For a binary endpoint, each participant is classified according to whether the event occurred. The arm-level event count is the number of participants classified as having the event, while the arm size describes the number of participants in that group. A risk, or event proportion, relates those quantities. Here, the registry describes the outcome as a count of participants and reports 15 of 15 in the nifedipine arm and 21 of 21 in the indomethacin arm. The registry does not separately give event definitions or participant-level records, so the counts cannot be checked against individual outcome histories.

A risk difference expresses the contrast between the event proportions in the two groups. A value of 0.0 indicates that the reported point estimates are the same on the risk-difference scale. A relative risk compares the event proportion in one group with that in the other; the reported value of 1.0 likewise represents no difference in the point estimates on that scale. These are distinct ways of expressing a comparison. They do not supply information about whether the result is sufficiently precise to rule out differences that could matter.

What does a confidence interval add?

A confidence interval describes uncertainty around an estimate under the statistical model and method used to construct it. In general, a wider interval indicates that the data and method are compatible with a broader range of values; a narrower interval indicates a more restricted range under those assumptions. An interval is not a guarantee that the true value lies within its limits, nor does it account automatically for problems such as selection bias, inaccurate measurement, or missing data.

The registry’s risk-difference interval is reported as 0.0 to 0.0, and the relative-risk interval as 1.0 to 1.0. Both are intervals with no displayed width. The registry does not state the interval method or explain this result. A reader should not infer that sampling uncertainty has disappeared simply because the reported limits coincide. The outcome counts are at the boundary where all listed participants have the event, and ordinary interval methods can behave differently at such boundaries. Without a named method and supporting analysis details, the statistical meaning of these limits cannot be evaluated fully.

Why are analysis details important?

For a randomized study, analysis choices include which participants are included, how participants are kept in their assigned groups, how missing outcomes are treated, and which statistical method is used. An analysis based on assigned groups generally aims to preserve the benefits of randomization. An analysis restricted to participants with complete outcome information can be affected if missingness is related to treatment or outcome. The registry does not report the analysis population, missing-data approach, or whether the randomized assignments were retained in the analysis.

The record lists no analyses and does not provide a p-value or a statistical test. A p-value, when reported, addresses how compatible data are with a specified null model under assumptions; it is not the probability that the null hypothesis is true, and it does not describe the size or clinical importance of an effect. Since no p-value is reported, none should be inferred from the interval or the arm counts. The point estimates and interval are the comparison statistics available in the registry record.

Random allocation and an unmasked design describe different parts of the study. Random allocation concerns how treatment groups are formed; masking concerns whether participants or study personnel know assigned treatment. The registry reports randomization and no masking, but does not report sequence generation, allocation concealment, or masking of outcome assessors. These omissions do not establish that procedures were inadequate, but they mean readers cannot assess those aspects from the record.

What can planning calculations tell a reader?

Sample-size planning is distinct from analysis of the observed trial. The registry’s planning illustration is described as using a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. The record also states that this is a planning illustration based on the observed effect, not the trial’s own design. No trial-specific sample-size justification or planning result is reported in the registry record.

A planning calculation asks how many participants might be needed under chosen assumptions to detect an effect at a specified power. It does not establish the power of the completed study after the outcome data are observed. In particular, a calculation anchored to an observed effect is sensitive to the observed estimate and should not be treated as independent confirmation of that estimate. The registry does not report a protocol-based effect assumption or a justification for the enrollment of 36. The illustration therefore cannot explain whether the completed enrollment met the study’s original aims.

General statistical interpretation also depends on the number of outcome events, the size of the treatment groups, and the method used. At boundary counts, some conventional estimates or intervals can be unstable or may require methods designed for sparse data. This is a general methodological point, not a claim about which method the investigators used. The registry does not name its method, so it is not possible to determine whether special handling was applied or whether the displayed interval reflects a particular software or coding convention.

The most defensible statistical reading keeps the reported quantities separate from what is unknown. The counts and point estimates are recorded. The width of the reported intervals is zero as displayed. But the analysis method, outcome ascertainment, participant flow, missing data, and inferential test are not reported. Those absences limit conclusions about precision and robustness, even when the numerical comparison appears simple.

10. Confidence Intervals and Precision

Precision concerns how narrowly the data and statistical method constrain an estimate. The registry reports a risk difference of 0.0 with limits of 0.0 and 0.0, and a relative risk of 1.0 with limits of 1.0 and 1.0. These intervals display no spread around their point estimates. Read literally, they communicate no uncertainty, but the record does not name the interval method or provide enough analysis detail to establish that such exactness is warranted.

That qualification is important because the reported outcome counts are 15 of 15 for nifedipine and 21 of 21 for indomethacin. Estimates at the boundary of all participants having the event can require careful statistical treatment. General interval methods may produce different results in such circumstances, and an interval’s meaning depends on the method and assumptions behind it. The registry does not identify those choices. The apparent zero-width intervals should therefore not be taken as proof that the treatment contrast is known exactly.

The arm sizes are also limited: the registry reports 15 and 21 participants. The record gives no trial-specific precision target, detectable-effect target, or sample-size justification. It does not report a p-value or an analysis explaining whether the displayed intervals are adjusted or otherwise modified. Consequently, the numerical intervals alone cannot support a strong conclusion about the range of plausible treatment effects.

A confidence interval is not a measure of all uncertainty. It does not account automatically for uncertain outcome definitions, incomplete follow-up, bias in outcome assessment, or departures from the analysis plan. The registry does not report sufficient detail to assess these factors. In practical reading, the identical point estimates are clear as recorded, but their apparent precision is not independently assessable from the registry information.

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when researchers examine multiple outcomes, comparisons, subgroups, or interim results. As the number of statistical questions grows, the chance of finding a nominally notable result by chance can increase unless the analysis plan addresses that issue. General methods include prespecifying a primary question, controlling error across a family of tests, or clearly labeling additional analyses as exploratory.

The registry lists one outcome measure and reports no secondary outcomes. It lists zero analyses. It does not describe an adjustment for multiple comparisons, a hierarchy of outcomes, subgroup analyses, or interim analyses. These details are not reported in the registry record, so it is not possible to determine whether multiplicity was relevant to analyses beyond the listed primary outcome or how it was handled.

Missing-data handling is also not reported. The arm counts sum to the recorded enrollment, but that does not establish that every randomized participant had complete outcome data or that all participants were included in the analysis. The registry does not report withdrawals, exclusions, loss to follow-up, reasons for missing observations, or imputation procedures. The outcome follow-up is described as the hospital stay, with an expected average of 1 week, but actual follow-up by participant is not given.

The analysis population is not reported. In randomized trials, whether the analysis includes participants according to their assigned groups can affect interpretation, particularly if treatment is discontinued, changed, or not received as planned. The record does not say whether the analysis followed assignment, included only participants who received treatment, or used another population. No conclusions about adherence or the analysis population should be inferred from the arm counts alone.

These omissions do not prove that multiplicity or missing data caused bias. They mean that readers cannot assess these issues from the registry record. The reported comparison should be interpreted as the result posted for the primary outcome, with the scope and handling of other analyses and incomplete observations unknown.

12. 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 events for 0 of 15 participants at risk in the nifedipine arm and 0 of 21 at risk in the indomethacin arm. It reports no deaths in either arm. For other adverse events, it records 1 of 15 participants at risk in the nifedipine arm and 0 of 21 at risk in the indomethacin arm. These figures are the safety counts in the registry record.

Serious adverse events and other adverse events are reported separately. A zero count means no event was recorded in the listed category among the participants at risk; it does not establish that an event could not occur or that the treatments have identical safety profiles. The record does not provide serious adverse event terms, and it does not describe how events were defined, collected, graded, or judged to be related to treatment. It also does not report the observation period for these safety counts separately from the stated hospital-stay follow-up.

These data are limited in scale and should not be treated as a comprehensive comparison of safety. The small arm sizes and absence of event-detail reporting make it difficult to interpret rare or clinically distinct harms. The single other adverse event recorded in the nifedipine arm is a count, not evidence by itself that the event was caused by treatment. No medical advice or treatment conclusion follows from these registry counts.

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

The posted results report equal point estimates for the primary outcome comparison: the risk difference is 0.0 and the relative risk is 1.0. The arm-level outcome counts are 15 of 15 for nifedipine and 21 of 21 for indomethacin. These values describe what the registry record reports for delay of preterm delivery by 48 hours. They do not establish that the medications have equivalent effects or that either treatment is superior.

Equivalence is a specific research claim. It ordinarily depends on a prespecified margin defining what degree of difference would count as acceptably small, together with an analysis precise enough to exclude differences outside that margin. The registry does not report an equivalence or non-inferiority objective, a margin, or a trial-specific precision justification. A point estimate of no difference is not by itself evidence of equivalence.

The displayed confidence intervals have identical lower and upper limits, but the registry does not identify the statistical method used to obtain them. They cannot be interpreted as proof of certainty. The outcome counts place every listed participant in the event category, and the record does not explain the outcome ascertainment or analysis procedures. These gaps matter when judging whether the posted numbers provide a reliable estimate of the treatment contrast.

The trial record also cannot answer broader questions that are not represented by the primary outcome. It lists no secondary outcomes and no analyses. The safety counts report no serious adverse events or deaths and one other adverse event in the nifedipine arm, but event definitions and details are absent. The record does not report longer-term outcomes, participant characteristics, adherence, or treatment changes. Results for delay by 48 hours should not be generalized to outcomes that were not reported.

In short, the registry records matching treatment-group point estimates for the primary endpoint, along with limited safety counts. The small enrollment, missing analysis details, and lack of outcome-definition information limit what can be concluded about the precision and broader meaning of those estimates. The record supports a description of the posted data, not a treatment recommendation or a conclusion about clinical benefit.

14. Why This Trial Matters Statistically

This trial raises statistical questions that are useful beyond this particular comparison. A randomized design can support a fair treatment comparison, but interpreting the estimate still depends on how allocation was carried out, how outcomes were measured, and which participants were analyzed. The registry identifies the study as randomized and unmasked, while leaving several of those implementation details unreported.

The primary outcome is a participant count for a binary event. Such outcomes can be easy to communicate, but their analysis depends on having a clear event definition and reliable classification. Here the recorded event count equals the reported arm size in each group, and the comparison intervals have no displayed width. That combination makes it especially important not to equate a simple result with a fully interpretable one. Readers need method details to understand what the estimate and interval represent.

The record also illustrates why an observed point estimate and a planning calculation answer different questions. A planning illustration based on the observed effect is not the study’s original design justification and is not observed power. The registry does not report a trial-specific sample-size rationale. Without that information, readers cannot tell how the enrollment target was selected or whether the study was designed to estimate a particular effect with a specified level of precision.

Finally, sparse reporting about missing data, analysis populations, and safety event definitions constrains reproducibility and critical appraisal. These are not merely technical details: they affect whether readers can trace how the reported counts were generated and determine which conclusions are supported. The trial is statistically informative as an example of why numerical estimates should be read alongside the methods and data definitions needed to interpret them.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several limitations are specific to the information in this trial record. The enrolled sample is 36, with 15 participants assigned to nifedipine and 21 to indomethacin. The registry does not explain the imbalance or report a sample-size justification. Its summary says that 450 participants would be asked to participate across all study sites, but does not explain how that statement relates to the recorded enrollment. This leaves recruitment context and intended study scale unclear.

The study is reported as randomized but unmasked. The registry does not describe sequence generation, allocation concealment, assessor masking, or implementation procedures. It does not report participant characteristics or detailed eligibility criteria beyond the outcome description’s reference to threatened preterm labor prior to 32 weeks of gestational age. These omissions restrict assessment of how the groups were formed and to whom the results may apply.

The primary endpoint is named, but its operational definition and ascertainment procedures are not described. The record reports counts equal to the arm sizes, yet does not provide participant-level data or an explanation of how the event was classified. The risk difference and relative risk intervals have identical limits, and no interval method is named. No p-value or analysis details are reported, and the record lists zero analyses.

There is also no reported account of withdrawals, missing outcomes, treatment adherence, protocol deviations, or the analysis population. The safety record gives only aggregate counts, with no serious adverse event terms or event descriptions. No secondary outcomes are listed. These are limits on what can be learned from the registry record; they do not establish that the underlying study failed to collect or analyze such information.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Comparison of Nifedipine Versus Indomethacin for Acute Preterm Labor — NCT03129945.
• Registry record last updated 2021-11-05; status last verified 2021-10.
• Results first posted 2021-11-05.
• 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.

19. Record Summary

NCT03129945 is a completed, randomized, parallel-group, unmasked study comparing oral nifedipine with oral indomethacin for premature obstetric labor. The registry reports enrollment of 36, a start date of 2017-01-17, and a primary completion date of 2019-04-18. The primary outcome is the number of participants with delay of preterm delivery by 48 hours; follow-up is described as the hospital stay, with an expected average of 1 week.

The outcome counts are 15 of 15 in the nifedipine arm and 21 of 21 in the indomethacin arm. The reported risk difference is 0.0 and the relative risk is 1.0, with identical lower and upper limits for each interval. Serious adverse events and deaths are reported as 0 in both arms; one other adverse event is recorded in the nifedipine arm and none in the indomethacin arm.

The registry does not report analysis methods, a p-value, an analysis population, missing-data handling, or a trial-specific sample-size justification. The posted estimates should be read with those limitations in mind.