Foley Bulb With Oral Misoprostol for Induction of Labor: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Foley Bulb With Oral Misoprostol for Induction of Labor (NCT03407625), a randomized na study. The primary outcome is Number of Participants With Vaginal Delivery.

2. Clinical Question

3. Trial Design

This was a prospective, cluster-randomized clinical trial with a parallel design and no masking. It compared Foley bulb plus oral misoprostol with oral misoprostol alone for induction of labor. The trial was sponsored by the University of Texas Southwestern Medical Center and is recorded as completed. The registry lists enrollment as 2227. The recorded start date is 2018-01-01, and primary completion is dated 2019-05-13.

The trial summary describes the study population as women with term pregnancies requiring induction of labor. It frames the comparison around mode of delivery, noting that many induction trials evaluate time to delivery. The primary outcome was the number of participants with vaginal delivery at the first induction, measured at delivery.

The combination arm was described as an initial transcervical Foley bulb followed by oral misoprostol 100 micrograms every 4 hours for a maximum of 2 doses. The comparator arm was oral misoprostol at the same stated dose and interval, also for a maximum of 2 doses. The registry record does not give further operational detail about how clusters were defined, how many clusters were assigned to each method, or how cluster assignment was implemented. Those details matter for understanding the design and analysis, but should not be inferred from the description alone.

Other listed outcomes include time to delivery, indication for cesarean delivery, oxytocin dose, time with Foley bulb in place, chorioamnionitis, and use of analgesia or anesthesia. Detailed results for these outcomes are not reported in the registry record. The record reports one analysis for the primary outcome and identifies log-binomial regression as the sponsor’s method.

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 Vaginal Delivery, measured over at delivery.

The primary endpoint is the number of participants with vaginal delivery at the first induction, assessed at delivery. It is a binary outcome at the participant level: each participant either had a vaginal delivery at the first induction or did not. The registry labels the result as a count of participants, rather than a continuous measure such as time to delivery.

Mode of delivery is directly relevant to the trial’s stated focus. The registry summary notes that studies of induction often emphasize time to delivery, whereas this trial compares methods using delivery mode as its primary outcome. This makes the endpoint a way to assess whether the proportion of participants with vaginal delivery differs between the assigned induction approaches. The registry does not report a separate definition of vaginal delivery or additional details about how the first induction was distinguished from any later care.

For a binary outcome, a risk ratio expresses the relative outcome frequency in one group compared with another, according to the contrast used in the analysis. The sponsor reported a risk ratio of 1.00. A value of 1 represents equal estimated risks under the coded contrast; the confidence interval describes the precision of that estimate. Because the registry does not explicitly map the analysis group codes to the treatment labels in the reported result, the numerical estimate should be read as the sponsor’s reported comparison rather than assigned an unsupported direction.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record reports a log-binomial regression analysis for the primary binary outcome. This method models the probability of an outcome using a logarithmic link and can estimate a risk ratio directly. In general, a risk ratio compares the outcome risk in one group with the risk in another. Its null value is 1, corresponding to equal risks under the stated contrast. The registry reports an estimate of 1.00 and a 95% confidence interval from 0.95 to 1.05.

What does the confidence interval express?

In general, a confidence interval describes the statistical uncertainty around an estimate under the model and its assumptions. A 95% confidence interval is produced by a procedure that, over repeated studies under those assumptions, would cover the target value in 95% of intervals. It is not a statement that there is a 95% probability that the true value lies within this particular interval. For this trial, the reported interval includes the risk-ratio null value of 1 and allows values below and above it. It therefore communicates more than a binary conclusion from a significance test: it shows the range of relative effects compatible with the analysis at the stated confidence level.

How should the p-value be read?

The reported p-value is 0.86. In general, a p-value measures how unusual the observed data, or data more extreme, would be if the null hypothesis and the statistical model were correct. It does not measure the size or clinical importance of an effect, and it is not the probability that the null hypothesis is true. Read alongside the interval, it indicates that the analysis did not identify a statistically clear departure from the null. It does not establish that the two approaches have identical outcomes.

Why does cluster randomization matter?

In a cluster-randomized trial, groups of participants rather than necessarily individual participants are the units assigned to study approaches. Participants in the same cluster can share circumstances and may have correlated outcomes. In general, treating correlated observations as if they were fully independent can make uncertainty estimates too small and statistical tests misleading. The appropriate analysis needs to account for the assignment structure. The registry reports that the sponsor used log-binomial regression and identifies the design as cluster-randomized, but detailed information about the clusters and the model’s handling of clustering is not reported in the registry record.

This is why a simple individual-level recalculation from group-level outcome summaries would not be an adequate substitute for the reported analysis. The registry record explicitly cautions that such a re-analysis would be misleading, and only the sponsor’s own analysis is shown. The reported sponsor estimate, confidence interval, and p-value should therefore be kept distinct from any hypothetical calculation that ignores the design. No independent recalculation is reported.

What does the endpoint’s binary form imply?

The primary endpoint records whether a participant had vaginal delivery at the first induction. For binary outcomes, analysis can compare risks or proportions between groups. The reported risk ratio is a relative measure rather than an absolute difference. The registry does not report primary outcome counts by group or an absolute risk difference, so neither can be reconstructed from the recorded estimate. The risk ratio’s contrast direction is also not explicitly mapped to the two treatment names in the analysis result.

In general, an estimate near 1 with an interval spanning 1 indicates that the data are compatible with the null value as well as with some relative differences. The range and width of the interval are essential to judging precision. Statistical evidence against the null and evidence that two approaches are sufficiently similar for a specific decision are different questions; the latter requires a prespecified equivalence or non-inferiority framework, which is not reported in the registry record.

How should planning calculations be distinguished from trial results?

Any sample-size figures associated with planning illustrations are not observed outcomes and are not observed power. The registry’s stated illustration assumptions use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation, with the effect to detect set as a stated proportion of the observed effect. Such calculations describe hypothetical future planning under those assumptions. They do not show the probability that this completed trial detected an effect, and they do not reveal the trial’s original design justification. The trial’s own sample-size justification is not reported in the registry record.

The registry lists 24 outcome measures and one analysis for the primary result. The record does not explain how the outcome measures were organized, whether multiple testing adjustments were planned, or whether the reported primary analysis was selected from a larger set of possible analyses. Those omissions limit assessment of the broader statistical plan. The methods should be interpreted only to the level of detail stated: log-binomial regression, a risk-ratio estimate, a 95% confidence interval, and a p-value for the primary outcome in a cluster-randomized trial.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Foley Bulb Plus Oral Misoprostol", "Oral Misoprostol")
n      <- c(1117, 1110)
events <- c(869, 860)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Foley Bulb Plus Oral Misoprostol  1117  869  77.8  75.2  80.2  75.3  80.1  75.3  80.1
ARM  Oral Misoprostol  1110  860  77.5  74.9  79.9  74.9  79.8  74.9  79.8

11. Analyses Reported by the Sponsor

The reported result is the sponsor’s own analysis: log-binomial regression produced a risk ratio of 1.00, with a 95% confidence interval from 0.95 to 1.05 and p = 0.86. The record identifies the study as cluster-randomized and cautions that an individual-level re-analysis would be misleading. For that reason, no simple recalculation from the posted summary statistics is presented. Such a calculation would not adequately reproduce the sponsor’s handling of the cluster design and could give an inappropriate account of uncertainty.

The sponsor’s analysis therefore takes precedence over an unadjusted re-calculation. The reported estimate should be read as the result of the analysis described in the registry, not as a result independently verified by reconstructing participant-level data. The registry record does not provide enough detail to reproduce the regression or assess all its specifications. It also does not map the reported group codes explicitly to the intervention labels, so the result is best stated without assigning a treatment direction that the record does not establish.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists 24 outcome measures and reports one analysis for the primary endpoint. It does not report how the multiple outcomes were organized into primary, secondary, or exploratory families for statistical testing, nor whether any adjustment for multiple comparisons was planned or applied. Without that information, it is not possible to assess how the reported p-value fits into a broader multiplicity strategy. The primary result should be read as the stated analysis rather than as evidence that all outcome comparisons were controlled for repeated testing.

The registry identifies vaginal delivery at the first induction as the primary outcome and gives a timeframe of at delivery. It does not report how missing primary outcome data were handled, whether any participants were excluded from the analysis, or the size and reasons for any missingness. An analysis population, such as intention-to-treat or per-protocol, is not reported in the registry record. The result therefore cannot be assumed to represent a particular analysis population or a specified missing-data procedure.

The cluster-randomized design is important to this interpretation. The record does not detail the cluster definitions, the number of clusters, or how the analysis incorporated clustering. It reports log-binomial regression and cautions against a simple individual-level re-analysis, but does not give enough methodological detail to independently reproduce the sponsor’s model. The sponsor’s result should be retained as reported, while recognizing that some design and analysis details are not available in the record.

The registry lists one primary analysis, but does not report whether other prespecified primary analyses, sensitivity analyses, interim analyses, or subgroup analyses were planned. Their presence or absence cannot be inferred from the single analysis reported. The statistical analysis plan and detailed missing-data strategy are not reported in the registry record.

13. 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 records zero serious adverse events in the Foley bulb plus oral misoprostol group among 1117 participants at risk, and zero in the oral misoprostol group among 1110 participants at risk. It also records zero other adverse events in each group and zero deaths in each group. No serious adverse event terms are listed.

These figures describe what was reported in the registry; they do not establish that no adverse events occurred beyond those captured or reported. A count of zero does not by itself show that the risk is zero, and it does not provide a precise estimate of the range of possible risks. The record does not give further details about adverse-event definitions, collection procedures, observation periods, or how the at-risk counts were determined. Those details are not reported in the registry record.

Safety counts should be interpreted separately from the primary efficacy analysis. They do not alter the reported risk ratio for vaginal delivery and do not provide a complete assessment of the benefit-risk profile. The registry lists no serious event terms, but the available record does not describe the full clinical context of safety monitoring or event ascertainment.

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

The result means that the sponsor’s reported model estimated a risk ratio of 1.00 for vaginal delivery at the first induction, with a 95% confidence interval from 0.95 to 1.05 and p = 0.86. The estimate is at the null value for a risk ratio, and the interval includes that value. Under the reported analysis, the data do not provide a statistically clear difference from the null. The interval also indicates that the result is not exact: it remains compatible with relative differences on either side of 1.

This is not proof that the two induction approaches are equivalent. Establishing equivalence requires a prespecified range of differences considered unimportant and an analysis designed to test whether the result falls within that range. The registry record does not report an equivalence margin or an equivalence analysis. Nor does it report a non-inferiority margin or a non-inferiority analysis. A non-significant result cannot substitute for either design.

The result also does not show that either approach is preferable for every participant or clinical circumstance. The reported endpoint concerns vaginal delivery at the first induction, and the registry record does not provide the primary outcome counts by group, detailed participant characteristics, or the other outcome results listed. It does not report the group-code mapping for the risk-ratio contrast, so direction should not be inferred beyond the sponsor’s stated estimate.

The record’s safety figures list zero serious adverse events, zero other adverse events, and zero deaths in both groups, using the recorded at-risk counts. These reports should not be read as proof that risk is absent, particularly without details on event definitions and ascertainment. Overall, the available registry result is a precise statement about the sponsor’s primary analysis, not a complete account of all outcomes, all possible harms, or every question relevant to choosing an induction approach.

15. Why This Trial Matters Statistically

This trial is statistically notable because the intervention was assigned through a cluster-randomized design, while the primary outcome was recorded for individual participants. Cluster assignment can create dependence among outcomes within a cluster. Analyses that ignore this structure may misstate uncertainty, so the design is not a minor technical detail. The registry specifically warns that a simple individual-level re-analysis would be misleading and presents the sponsor’s own analysis instead.

The primary endpoint also reflects a choice to focus on mode of delivery rather than only time to delivery. The registry summary explicitly places this choice in the context of induction studies that often evaluate time to delivery. Statistically, defining a clear primary outcome helps direct attention to a specific comparison, although the registry does not report the full analysis plan or how the other listed outcomes were treated.

The reported risk ratio of 1.00 and confidence interval from 0.95 to 1.05 illustrate why an estimate and its precision should be read together. A point estimate at the null does not establish equality, and a p-value alone cannot convey the range of effects compatible with the analysis. The confidence interval communicates uncertainty, while the missing equivalence framework prevents treating the result as a formal demonstration of equivalence.

The record also highlights the importance of transparent reporting. Information about cluster definitions, outcome counts by group, missing data, analysis populations, and multiplicity procedures would help readers evaluate the result more fully. Their absence does not invalidate the sponsor’s reported analysis, but it limits independent assessment and reproduction. The trial therefore offers a useful example of interpreting a model-based result in the context of a cluster-randomized design while keeping statistical evidence, precision, and design limitations distinct.

16. 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 how clusters were defined, how many clusters were involved, or how cluster assignment was carried out. These details are important for understanding the randomization and the dependence structure in the data. Although the sponsor’s analysis is identified as log-binomial regression, the record does not describe its cluster adjustment or other model specifications, limiting independent evaluation and reproduction.

The primary outcome result is reported as a risk ratio with a confidence interval and p-value, but primary outcome counts by treatment group are not reported. The analysis group codes are not explicitly mapped to the two treatment labels in the result. Consequently, the estimate should not be converted into group-specific risks or presented with a direction that is not established by the record. The analysis population and missing-data handling are also not reported.

The registry lists 24 outcome measures but does not describe a multiplicity strategy, an analysis plan for the other outcomes, or whether interim or sensitivity analyses were planned. The sample-size justification for the trial is not reported. Planning illustrations based on the observed effect do not replace the original design rationale and should not be interpreted as observed power.

Participant characteristics, detailed eligibility criteria, and results for the listed secondary outcomes are not reported in the registry record. The safety entry gives event counts but not event definitions, ascertainment procedures, or follow-up details. These reporting gaps limit assessment of generalizability, the completeness of outcome capture, and the broader interpretation of benefits and harms. The sponsor’s reported primary result remains the appropriate result to quote, with these limitations kept in view.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Foley Bulb With Oral Misoprostol for Induction of Labor — NCT03407625.
• Registry record last updated 2020-11-04; status last verified 2020-10.
• Results first posted 2020-11-04.
• 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.

20. Record Summary

The registry record describes a completed, prospective, parallel, cluster-randomized trial with no masking. It compared an initial transcervical Foley bulb followed by oral misoprostol with oral misoprostol alone for induction of labor in women with term pregnancies requiring induction. Both arms used oral misoprostol 100 micrograms every 4 hours for a maximum of 2 doses. Enrollment is recorded as 2227.

The primary outcome was the number of participants with vaginal delivery at the first induction, assessed at delivery. The sponsor used log-binomial regression and reported a risk ratio of 1.00, a 95% confidence interval from 0.95 to 1.05, and p = 0.86. The record cautions against an individual-level re-analysis because of the cluster-randomized design. It lists zero serious adverse events, zero other adverse events, and zero deaths in both treatment groups.

Further detail about the cluster structure, group-code mapping, missing data, analysis population, multiplicity handling, and results for secondary outcomes is not reported in the registry record.