Foley Bulb Traction for Cervical Ripening: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Foley Bulb Traction for Cervical Ripening (NCT00976703), a randomized na study. The primary outcome is Time to Delivery.

2. Clinical Question

The clinical comparison concerns two ways of applying traction to a cervical Foley catheter before induction of labor. The study is described as randomized, with the two approaches assigned in a parallel-group design. It is unmasked, so participants and study personnel were not described as blinded to the traction method.

The registry's brief summary frames the comparison around cervical dilation after ripening and the length of labor. It states a hypothesis that the weighted bag would increase the proportion reaching post-ripening dilation of at least 3 cm and shorten average labor. However, the posted primary outcome measure is time to delivery, reported as a continuous measure in hours. The registry summary and the posted primary measure therefore do not present the primary question in exactly the same way.

The posted result compares mean time to delivery for the weighted-bag and leg-taping groups. The registry also lists patient pain or comfort and time to Foley expulsion among secondary outcomes. The available record does not give outcome results for those measures, and it does not report results for post-ripening dilation or method of delivery. The principal interpretation must therefore stay with the time-to-delivery result that is posted.

3. Trial Design

The registry describes a randomized, unmasked, parallel-group trial comparing weighted-bag traction with leg taping for cervical ripening using a Foley catheter before induction of labor. The sponsor was MetroHealth Medical Center. The record lists the study as completed and reports enrollment of 197. The intervention descriptions distinguish the two traction methods: a saline bag was used to create gravity traction in one group, while the catheter was attached to the inner thigh in the other.

The reported arm results include 96.0 participants in the weighted-bag group and 95.0 in the leg-taping group. The primary outcome is time to delivery, measured in hours and summarized by a mean and standard deviation. The registry describes the measurement timeframe as an average of 20 hours, up to 40 hours. The weighted-bag group had a mean time to delivery of 19.8 hours with a standard deviation of 8.5; the leg-taping group had a mean of 18.8 hours with a standard deviation of 8.0.

The registry's design description states that its planning target was to find a 20% difference with a 40% standard deviation, 90% power, and alpha of 0.05. It says the investigators estimated a need for 86 patients in each arm and aimed to recruit 194 to account for potential dropouts and missing data. These are the design assumptions and targets described in the record; they are distinct from the later planning illustration based on the observed effect.

The registry summary describes post-ripening dilation of at least 3 cm and time to delivery as primary outcomes. Its posted primary result, however, is time to delivery. The listed secondary outcomes are patient pain or comfort rating and time to Foley expulsion. Although the summary also mentions method of delivery as a secondary outcome, outcome results for it are not reported in the registry record. The full eligibility criteria, allocation-concealment procedures, protocol details, and analysis populations 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.

Before assignment: Eligibility criteria included: admission for an induction of labor, a fetus in cephalic presentation, and an unripe cervix defined as a Bishop score ≤ 6.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: In order to find a 20% difference with a 40% standard deviation, power of 90%, and alpha of 0.05, we estimated we needed 86 patients in each arm. We aimed to recruit 194 patients to account for potential dropouts and missing data.

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 Time to Delivery, measured over an average of 20 hours, up to 40 hours.

Time to delivery measures the elapsed time from the relevant starting point in the induction process to delivery, expressed in hours. The registry identifies it as a continuous primary outcome, summarized by the group mean and standard deviation. The recorded timeframe is an average of 20 hours, up to 40 hours. The exact operational definition of when timing began and how delivery time was recorded is not reported in the registry record.

This endpoint is used to assess the duration of the process rather than only whether a particular threshold was reached. A mean provides a single summary of the average observed time in each group, while the standard deviation describes the spread of individual times around that average. Those summaries allow an unadjusted comparison of the two group means, but they do not describe every participant's experience or the full shape of the time distribution.

Time to delivery is distinct from the registry summary's other stated outcome of post-ripening dilation of at least 3 cm. That dilation outcome is expressed as a threshold, whereas time to delivery is continuous. The posted result available for interpretation is the latter. Results for dilation, pain or comfort, time to Foley expulsion, and method of delivery are not reported in the registry record. As a result, the posted time-to-delivery comparison cannot by itself describe all the clinical outcomes mentioned in the study summary.

7. Results Posted in the Registry

• Leg Taping (Taping): mean 18.80 versus 19.80 on control; difference -1.00 (95% CI -3.34 to 1.34), standardized effect d = -0.12; z-test p = 0.402.

8. Statistical Interpretation

9. Statistical Methods Explained

What does the mean difference represent?

The primary outcome is continuous, measured in hours, and summarized with a mean in each group. The comparison is expressed as the leg-taping mean minus the weighted-bag mean. Its estimate is -1.0 hours. A negative value means the observed mean was lower in the leg-taping group; it does not on its own establish that the groups differ beyond what could plausibly arise from sampling variation. The calculation is unadjusted and is based on the posted group summaries.

A mean is a compact summary of a set of observations. It is useful for comparing average times, but it does not show how individual times are distributed. The standard deviation gives information about variation within a group: larger spread means individual observations tend to be farther from the group mean. The reported standard deviations are 8.5 hours for weighted bag and 8.0 hours for leg taping. These summaries do not reveal whether the observations follow a symmetric pattern, include extreme values, or cluster in distinct ways.

What does the confidence interval add?

The confidence interval for the mean difference runs from -3.341 to 1.341 hours. It represents a range of values reasonably compatible with the data and the assumptions used to form the interval. Because the range includes zero, the posted result does not distinguish a difference from no difference at conventional significance thresholds. Because it also includes values on either side of zero, it remains compatible with a shorter average time in either group. A confidence interval describes uncertainty in the estimate; it is not a range containing a fixed proportion of individual delivery times.

The registry result gives an unadjusted p-value of 0.402. In a statistical test framed around no mean difference, a p-value describes how unusual a result at least as discordant with that null model would be if the model and its assumptions held. It is not the probability that the null hypothesis is true, and it does not quantify clinical importance. A p-value alone cannot tell whether the estimate is precise; the confidence interval is more informative about the range of values compatible with the data.

Why do the outcome type and analysis matter?

Time to delivery is recorded as a continuous mean, not as a binary event or a time-to-event analysis in the posted result. The registry record does not report whether delivery times were censored, how missing times were handled, or whether a survival-analysis method was used. The stated timeframe is an average of 20 hours, up to 40 hours, but the exact timing origin and analysis handling are not reported. Those details matter because different definitions and methods can lead to different interpretations of an average duration.

The trial is described as randomized, unmasked, and parallel-group. Random assignment is intended to make comparison groups similar on average, including for characteristics that were not measured. It does not guarantee balance in a particular trial, and the record does not provide baseline characteristics or details of the randomization procedure. Lack of masking can affect aspects of care or outcome assessment, although the extent of any such effect cannot be determined from this record. Time to delivery is a time-based measure, but it is not a subjective rating; the way it was recorded and assessed is not reported in the registry record.

Why can variation affect a comparison?

When individual values vary considerably within groups, the group means may be estimated less precisely than when observations are tightly clustered, all else equal. The reported standard deviations show meaningful variation in both groups compared with the observed separation in their means. The standard deviations do not, by themselves, establish whether a normal-distribution model is appropriate. The recalculated comparison uses the posted summary statistics and an unadjusted approach; it should not be confused with an analysis that accounts for other variables or uses a model tailored to a different distribution.

General statistical context: over-dispersion means the data vary more than a chosen model expects. When that occurs, standard errors can be too small if the model does not allow for the extra variation, making confidence intervals too narrow and tests too optimistic. The registry record does not report a model-based dispersion assessment for this endpoint. It is therefore not possible to say whether over-dispersion was evaluated or whether it affected the sponsor's analysis.

What is known about the sponsor's analysis?

The record reports the posted group means, standard deviations, sample sizes, mean difference, confidence interval, and unadjusted p-value. It does not report a detailed statistical analysis plan, adjusted estimates, interim analyses, or analysis-population definitions. It also does not report how missing outcome data were handled. Those omissions limit assessment of whether the posted comparison follows a prespecified analysis and how robust it is to analytic choices. They do not change the arithmetic meaning of the displayed unadjusted estimate, but they constrain broader interpretation.

The registry summary lists a dilation threshold and time to delivery as primary outcomes, while the posted primary result is time to delivery. The registry also lists patient pain or comfort and time to Foley expulsion as secondary outcomes, while its brief summary mentions method of delivery as well. The record does not report a multiplicity strategy for handling inference across multiple outcomes. General statistical context: when several outcomes are tested, the chance of at least one apparently notable result can rise unless the analysis accounts for multiple testing. No correction or hierarchy can be inferred from this record.

10. Confidence Intervals and Precision

The estimated mean difference in time to delivery is -1.0 hours, with a confidence interval from -3.341 to 1.341 hours. The interval is wide enough to include both a potentially shorter mean time with leg taping and a potentially shorter mean time with weighted-bag traction. It also includes zero, so the data do not provide a precise directional separation between the group means.

Confidence intervals are a way to express uncertainty in an estimated quantity. In general, an interval produced by a method with a stated confidence level would cover the true value at that rate across repeated use of the same procedure, if the assumptions held. The confidence level for this reported interval is not stated in the registry record, so it should not be assigned a level based on the appearance of the interval. The posted interval is an uncertainty range for the mean difference, not a range of individual delivery times.

The group means are close relative to the reported standard deviations: weighted bag has a mean of 19.8 hours and standard deviation of 8.5, while leg taping has a mean of 18.8 hours and standard deviation of 8.0. The variability within groups makes clear that individual delivery times differ considerably; the interval conveys uncertainty about the difference in averages, not the spread of those individual observations.

The unadjusted p-value is 0.402. It should be interpreted alongside the estimate and interval, not as a substitute for them. The interval shows that the result is not sufficiently precise to rule out differences in either direction. No adjusted confidence interval is reported in the registry record, and the interval's construction method is not reported. The result is therefore best described as an unadjusted estimate with substantial uncertainty, rather than as evidence of equivalence or proof that the methods produce identical times.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are illustrations based on the observed mean difference, not the original trial's design calculation. For this continuous time-to-delivery outcome, the listed figures are participants per arm. The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. These assumptions describe the illustration; they do not establish what methods were used in the original trial.

The 80% power column gives the illustrative number of participants per arm for a design with an 80% chance of detecting the specified effect under those assumptions, if that effect is real. The 90% power column gives the corresponding number per arm for a design with a 90% chance. These are design probabilities under a model, not probabilities that a result is true or that the treatment will produce the estimated effect. This is not observed power.

Planning for 100% of the observed effect gives 1,070 participants per arm for 80% power and 1,433 for 90% power. Planning for 75% of the observed effect gives 1,902 per arm for 80% power and 2,546 for 90% power. Planning for 50% of the observed effect gives 4,280 per arm for 80% power and 5,729 for 90% power. The effect fractions are planning scenarios, not observed outcomes.

Smaller effects are harder to distinguish from random variation, so they require more participants to reach the same planned power under the stated assumptions. These large illustrative counts also reflect the small observed mean difference relative to the variability in the outcome. They should not be read as a retrospective judgment about whether the completed trial was adequately designed. The registry separately reports its original planning description: a target 20% difference, a 40% standard deviation, 90% power, alpha of 0.05, an estimated 86 patients in each arm, and a recruitment aim of 194. The record does not report whether those original planning assumptions were met in the final analysis.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -1.000; pooled standard deviation σ = 8.255.
2. n = 2 × (1.96 + 0.842)² × 8.255² / -1.000² = 1,069.8, rounded up to 1,070 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -1                      # observed difference in means
sigma <- 8.25510904814863                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(976703)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 1,070 (80% power), 1,433 (90% power)
 75% of observed effect: n per arm = 1,902 (80% power), 2,546 (90% power)
 50% of observed effect: n per arm = 4,280 (80% power), 5,729 (90% power)
power.t.test: 1070.7 
Simulated power at n = 1,070 per arm: 0.800 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry summary discusses more than one outcome: post-ripening dilation of at least 3 cm and time to delivery are described as primary outcomes, while patient pain or comfort and method of delivery are described as secondary outcomes. The listed secondary outcomes in the posted record are patient pain or comfort rating and time to Foley expulsion. The posted primary result is time to delivery. This mismatch in the descriptions makes it difficult to determine from the record how the outcomes were formally prioritized.

A multiplicity plan explains how inference is managed when several outcomes or comparisons are examined. General statistical context: testing many outcomes without adjustment can increase the chance of at least one apparently unusual result. The registry record does not report a multiplicity adjustment, outcome hierarchy, or statistical analysis plan that would clarify how multiple outcomes were handled. No correction, selection rule, or prespecified primary-outcome hierarchy should be inferred.

The record reports enrollment and outcome group sizes, but it does not report the analysis population, exclusions, or missing-data handling for time to delivery. The registry's design description says recruitment was intended to account for potential dropouts and missing data, but it does not state how missing observations were treated in the analysis. It is not reported in the registry record whether participants were analyzed according to assignment, whether any were excluded from the reported outcome, or how incomplete records affected the estimates.

The outcome measure is a duration, yet censoring procedures and the handling of participants without a recorded delivery time are not reported in the registry record. Nor are the timing origin, detailed measurement rules, or use of imputation described. These omissions matter because the analyzed group and missing-data assumptions can influence an estimate and its uncertainty. The available result can be described as the posted unadjusted comparison, but its relation to a full intention-to-treat analysis or another defined analysis population cannot be established from the record.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 1% reporting threshold.

The serious adverse event entries report 0 affected among 96 at risk in the weighted-bag group and 0 affected among 95 at risk in the leg-taping group. The other adverse event entries also report 0 affected in each group, with the same at-risk counts. These are counts recorded in the registry, not estimates of the rate of all possible harms.

Zero recorded events does not establish that no adverse events occurred, particularly when the record does not describe event definitions, monitoring methods, follow-up completeness, or how events were collected. The death counts are not reported in the registry record. The record also does not list serious adverse event terms. Without details on ascertainment and duration of follow-up, the entries should be read narrowly as the posted counts for the recorded categories, rather than as a comprehensive safety assessment.

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

The posted primary result compares average time to delivery between weighted-bag traction and leg taping. The weighted-bag group mean was 19.8 hours and the leg-taping group mean was 18.8 hours. The unadjusted mean difference, calculated as leg taping minus weighted bag, was -1.0 hours, with a confidence interval from -3.341 to 1.341 hours and an unadjusted p-value of 0.402. The interval includes zero and values on both sides, so the result does not establish a clear difference in average time.

This does not show that the methods are equivalent. Equivalence requires a defined margin and an analysis designed to establish that the plausible difference lies within that margin; such a margin and analysis are not reported in the registry record. Nor does the result prove that there is no difference. The uncertainty range leaves room for effects in either direction, and the posted estimate is an unadjusted comparison.

The comparison also does not establish what happened for every participant. A group mean can conceal variation in individual times and cannot describe the full distribution. The standard deviations, 8.5 hours for weighted bag and 8.0 hours for leg taping, indicate variation around the group averages. The record does not report distributional summaries, subgroup results, or an adjusted analysis that might address differences in participant characteristics.

The time-to-delivery estimate cannot answer every clinical question mentioned in the registry. Results for post-ripening dilation of at least 3 cm, patient pain or comfort, time to Foley expulsion, and method of delivery are not reported in the registry record. The available serious and other adverse event entries show 0 affected in each group, but the record does not provide enough information about ascertainment to conclude that no harms occurred.

Overall, the posted data describe a small estimated difference in group means with uncertainty spanning both directions. They do not establish a causal explanation for the observed means, demonstrate equivalence, or provide a complete assessment of the listed outcomes and safety. The interpretation is limited to the recorded randomized comparison and the outcome information available in the registry record.

16. Why This Trial Matters Statistically

This trial is statistically instructive because it places a point estimate beside its uncertainty. The difference in average time to delivery is -1.0 hours, but the confidence interval ranges from -3.341 to 1.341 hours. Focusing only on the point estimate could suggest a direction; considering the interval makes clear that the data are compatible with differences in either direction. That distinction is central to interpreting clinical research: an estimate is not the same as a precise conclusion.

The outcome also illustrates the difference between variation within groups and separation between group averages. The standard deviations are 8.5 and 8.0 hours, while the estimated difference is -1.0 hours. The averages summarize the groups, but the substantial spread means the mean difference alone does not describe individual experiences. Reporting both means and measures of variability helps readers understand that contrast.

The registry record offers two distinct kinds of planning information. It describes the original design target in terms of a 20% difference, a 40% standard deviation, 90% power, alpha of 0.05, and an estimated 86 patients in each arm, with a recruitment aim of 194. Separately, the planning illustration based on the observed effect shows how participant requirements can grow when the effect to detect is smaller. These are different planning contexts and should not be conflated.

The record also demonstrates why outcome definitions and analysis plans matter. Its summary mentions several outcomes, while the posted primary result focuses on time to delivery and the available secondary outcome list does not match every outcome mentioned in the summary. Missing details about multiplicity, missing data, analysis populations, and measurement procedures limit assessment of how the reported estimate fits into the full study plan. Those are substantive interpretation issues, not merely reporting details.

17. Limitations

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

Several trial-specific details needed to evaluate the result are not reported in the registry record. Eligibility criteria and participant characteristics are not given, so the group composition and the population to which the estimate might apply cannot be assessed. Details of random sequence generation and allocation concealment are also absent. Although the trial is described as randomized, the record does not allow evaluation of those procedures.

The study was unmasked. The record does not explain whether outcome recording was standardized or whether those assessing time to delivery could have been influenced by knowledge of the assigned traction method. The exact starting point for measuring delivery time and the procedures for recording it are not reported. The stated timeframe is an average of 20 hours, up to 40 hours, but the record does not clarify how that timeframe affected observation or analysis.

The posted endpoint result is an unadjusted mean comparison. Baseline data, adjusted results, distributional checks, and detailed model assumptions are not reported. Nor does the registry specify the analysis population, the treatment of missing outcome observations, or any censoring approach. These omissions prevent a full evaluation of the robustness of the estimate.

Outcome reporting is also incomplete or not fully aligned across the record. The brief summary describes post-ripening dilation and time to delivery as primary outcomes; the posted primary result is time to delivery. The summary mentions method of delivery, while the listed secondary outcomes are patient pain or comfort and time to Foley expulsion. Results for those outcomes and for dilation are not reported in the registry record. A multiplicity plan is not reported, so the role of the posted result among the intended outcomes is unclear.

The adverse event entries record no affected participants in the listed categories, but details of event collection, definitions, and follow-up are not reported. Death counts are not reported in the registry record. These limitations mean the posted record supports a narrow reading of the time-to-delivery comparison, rather than a comprehensive assessment of all study outcomes.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Foley Bulb Traction for Cervical Ripening — NCT00976703.
• Registry record last updated 2013-06-07; status last verified 2013-05.
• Results first posted 2013-06-03.
• 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.

21. Record Summary

NCT00976703, titled “Foley Bulb Traction for Cervical Ripening,” is a completed randomized, unmasked, parallel-group trial sponsored by MetroHealth Medical Center. It enrolled 197 participants and compared weighted-bag traction with leg taping during cervical ripening with a Foley catheter before induction of labor.

The posted primary outcome is time to delivery, measured in hours and summarized as a mean. The weighted-bag group had a mean of 19.8 hours and standard deviation of 8.5; the leg-taping group had a mean of 18.8 hours and standard deviation of 8.0. The unadjusted mean difference was -1.0 hours, with a confidence interval from -3.341 to 1.341 hours and an unadjusted p-value of 0.402.

The interval includes zero and values in both directions, so the result does not establish a clear difference in average time to delivery. Results for the other outcomes mentioned in the registry summary are not reported in the registry record. The record also does not report detailed analysis methods, missing-data handling, or a multiplicity plan.