Severing Nuchal Cord at the Time of Delivery.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Severing Nuchal Cord at the Time of Delivery. (NCT00345254), a randomized na study. The primary outcome is Umbilical Cord pH.

2. Clinical Question

The question concerns a measurable neonatal outcome associated with two delivery practices, not a broad assessment of every possible outcome of the practices. The primary endpoint is cord pH immediately after delivery. The registry record does not report a separate primary clinical threshold or a definition of what difference in pH would be considered important. It also does not report secondary outcomes in the posted results.

The study was randomized, which means assignment to the two approaches was intended to be determined by a random process rather than by a clinician's choice alone. Random assignment can help make groups comparable at baseline, but it does not by itself guarantee that the posted analysis accounts for missing measurements, protocol deviations, or all sources of bias. The registry record does not describe those details. The results should therefore be read as a comparison of the reported group summaries and analysis, with the information about conduct and analysis limited to what the record states.

3. Trial Design

The registry record describes a randomized, parallel-group study with no masking. Its enrollment is 60. The arm descriptions list 30 participants in the severing-cord group and 30 in the untouched-cord group. The brief summary says eligible women were to enter a randomization process after ultrasound diagnosis of a cord around the fetal neck during labor. The record does not describe the randomization sequence, allocation concealment, or who knew the assignment during care or outcome assessment.

The intervention was a delivery procedure: the cord was intentionally cut. The comparator was to leave the cord untouched. The arm descriptions place the action after delivery of the anterior shoulder and before extraction of the body. The brief summary instead describes cutting after delivery of the head. This difference in timing is present in the registry record and is not resolved there. The record identifies the study as parallel, meaning that participants were assigned to one group rather than crossing between the approaches.

The listed primary outcome is umbilical cord pH, summarized as a mean with a standard deviation and measured immediately after delivery. The posted group means are 7.29 for severing and 7.32 for untouched, with standard deviations of 0.07 and 0.06, respectively. The registry reports a two-sided t-test analysis. It does not report a protocol, detailed statistical analysis plan, sample-size justification, interim analysis plan, or analysis-population definition. Those details should not be inferred from the enrollment or the planning illustrations.

The registry record lists the study as completed. It reports no secondary posted outcomes. The sponsor is Wolfson Medical Center. Beyond these items, the record does not describe recruitment flow, departures from assigned treatment, missing outcome measurements, or the process by which the posted results were assembled.

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 Umbilical Cord pH, measured over immediately after delivery.

The primary endpoint is umbilical cord pH immediately after delivery. It is a continuous measurement, and the registry summarizes it using a group mean and standard deviation. The mean describes the central value of the measurements in each group; the standard deviation describes how spread out individual measurements were around that group mean.

As a general statistical and clinical concept, pH is used to characterize acidity and alkalinity. Cord pH can provide information about acid-base status around birth. Its value as an endpoint is that it is measured numerically and can be compared between randomized groups using summaries such as means and a mean difference. The registry record does not specify whether the measurement was from arterial or venous cord blood, the collection protocol, or any threshold used to classify a result.

The recorded means are 7.29 for the severing-cord group and 7.32 for the untouched-cord group. The posted comparison estimates the untouched-cord mean minus the severing-cord mean as 0.03. This describes the difference in the group averages; it does not indicate how each individual measurement was distributed, nor does it establish the importance of a difference for a particular infant. The record does not report a threshold for clinical importance or additional primary outcomes that would broaden the endpoint assessment.

7. Results Posted in the Registry

• Untouched Cord: mean 7.32 versus 7.29 on control; difference 0.03 (95% CI -0.00 to 0.06), standardized effect d = 0.46; z-test p = 0.075.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry summarizes the primary outcome as a continuous measure, using a mean and standard deviation for each group. A mean is the arithmetic average of observed values within a group. A standard deviation describes variation among individual observations around that average. These summaries provide a compact description, but they do not show the full distribution of individual pH values or reveal whether unusual observations affected the averages.

The comparison is a difference in means. Its direction is defined as the untouched-cord group minus the severing-cord group. The reported estimate is 0.03, with group means of 7.32 and 7.29, respectively. A positive estimate therefore means the untouched-cord group had the higher average in the posted comparison. The estimate concerns group averages, not a change within the same participant, and it does not describe the outcome of any particular individual.

The registry reports a two-sided t-test. In general, a t-test evaluates whether a difference in group means is compatible with a null hypothesis of no difference, under assumptions about the data and analysis. A two-sided test considers departures in either direction rather than specifying in advance that only a higher or only a lower mean matters. The registry's reported p-value is 0.1. The unadjusted recalculation from the posted summaries gives p = 0.075. A p-value is a measure of how unusual the observed data, or data more extreme, would be under the test's null hypothesis and assumptions; it is not the probability that the null hypothesis is true, and it does not measure clinical importance.

The recalculated comparison is based on the posted group means, standard deviations, and group sizes, using an unadjusted method. It is not an adjusted model that accounts for other characteristics or variables. The record does not report covariate adjustment, a prespecified model beyond the two-sided t-test, or the exact analysis population. The simple calculation should therefore be distinguished from the registry's own reported analysis and should not be interpreted as evidence that the sponsor used the same computational details.

A confidence interval for a mean difference gives a range of estimates compatible with the observed data under the calculation's assumptions. The posted interval runs from -0.003 to 0.063. Because zero lies within the interval, the data are compatible with no mean difference as well as with differences on either side of zero within that range. The interval's width conveys uncertainty, but its interpretation also depends on the method and assumptions used to construct it. The registry record does not provide further details about the interval method.

The standard deviation is relevant because individual measurements vary. In general, greater variability makes it harder to estimate a group mean precisely when the amount of information is unchanged. The pooled standard deviation listed for the comparison is 0.065. Pooling is a way of combining within-group variability for a comparison under an assumption that the groups can reasonably be described by a common variance. The record does not report diagnostics or a separate variance-model assessment. The posted standard deviations are 0.07 and 0.06, so the displayed group summaries give some sense of variation but do not establish that all model assumptions hold.

Randomization is intended to reduce systematic differences between groups at the time of assignment. A parallel design assigns each participant to one approach, so the group comparison is between separate assigned groups. The record identifies randomization and a parallel model, but does not describe the sequence-generation method, concealment, implementation, or masking of outcome assessment. It states that masking was none. These details matter when assessing whether allocation or outcome measurement could have been influenced by knowledge of assignment.

What does the p-value address?

In general, a p-value addresses compatibility between data and a specified null model, conditional on the analysis assumptions. It does not answer whether the estimated difference matters clinically, and it does not quantify the chance that a future study will obtain the same result. Here, the registry's two-sided test reports p = 0.1, while the unadjusted recalculation reports p = 0.075. The record does not explain why these values differ. They should be identified by their source rather than treated as interchangeable.

What can the planning illustrations tell readers?

The illustrations use the observed effect as a planning reference and consider smaller fractions of that effect. They show how the number of participants per arm changes under the stated assumptions when targeting 80% or 90% power. In general, a power target refers to a design's probability of detecting a specified effect under a model if that effect is present. These calculations are planning aids, not a description of the trial's original design and not a retrospective estimate of observed power. The registry record does not report the original sample-size assumptions or justification.

What remains unspecified?

The registry record does not report a detailed statistical analysis plan, handling of missing pH values, treatment of protocol deviations, an analysis-population definition, or whether any subgroup analyses were planned. It also does not report an interim analysis plan or whether any adjustment was planned for multiple testing. These omissions mean that the posted summary supports a focused reading of the listed comparison, but not a reconstruction of every analysis decision or an assessment of all potential sources of bias.

10. Confidence Intervals and Precision

The posted mean difference is 0.03, defined as the mean for the untouched-cord group minus the mean for the severing-cord group. Its confidence interval runs from -0.003 to 0.063. The interval includes zero, so the posted estimate is not precise enough to exclude no difference under the interval's assumptions. It also spans values on either side of zero, indicating uncertainty about the direction and size of the underlying mean difference.

In general, a confidence interval is a range produced by a statistical procedure that, over repeated use under its assumptions, would contain the target quantity at the procedure's stated coverage rate. It is not a range of individual participants' pH measurements, nor is it a probability statement about the true value after observing this particular interval. The registry record does not report the confidence level for this interval, so no level should be inferred from the posted bounds.

The p-value from the unadjusted recalculation is 0.075; the registry's reported two-sided test gives p = 0.1. These values are not identical, and the registry record does not explain the difference. The interval and p-values address statistical compatibility under their respective calculations, not clinical importance. No threshold for a clinically meaningful pH difference is reported. The absence of such a threshold makes it difficult to use the interval to distinguish clinically trivial from important differences.

The sample sizes listed for the groups and the observed variability help contextualize the estimate, but they do not remove its uncertainty. The interval should be read as a statement about the precision of the group-mean comparison, not as a guarantee that future results will fall within the same bounds. The registry record does not report further precision analyses or an adjusted interval.

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 participants per arm, not total events. The sample-size 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 as the stated fraction of the observed effect. These are planning assumptions for the illustration; the registry record does not report the trial's own original design assumptions or sample-size justification.

The 80% power column gives the participants per arm that the illustration estimates would be needed to have an 80% probability of detecting the specified effect under the stated assumptions, if that effect were present. The 90% power column gives the corresponding requirement for a 90% probability. The illustration lists 75 and 100 participants per arm for planning for 100% of the observed effect; 132 and 177 for planning for 75% of the observed effect; and 297 and 397 for planning for 50% of the observed effect, respectively for the 80% and 90% power targets.

The pattern reflects a general design principle: smaller effects are harder to detect and require more participants when the other assumptions are held fixed. A higher power target also requires a larger planned sample in these illustrations. The calculations use the observed effect as a reference, so their requirements depend on that estimate and on the assumptions. The registry record does not establish that these were the assumptions used when the study was originally designed.

This is not observed power. The figures are planning illustrations and do not tell whether the completed study had a particular probability of detecting an effect after its results were known. They should not be used as a replacement for reading the observed estimate and confidence interval.

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 = 0.030; pooled standard deviation σ = 0.065.
2. n = 2 × (1.96 + 0.842)² × 0.065² / 0.030² = 74.1, rounded up to 75 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 <- 0.0300000000000002                      # observed difference in means
sigma <- 0.0651920240520265                     # 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(345254)
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 = 75 (80% power), 100 (90% power)
 75% of observed effect: n per arm = 132 (80% power), 177 (90% power)
 50% of observed effect: n per arm = 297 (80% power), 397 (90% power)
power.t.test: 75.1 
Simulated power at n = 75 per arm: 0.801 (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. Analyses Reported by the Sponsor

The registry reports the sponsor's analysis as a two-sided t-test with p = 0.1. The unadjusted recalculation from the posted group summaries gives p = 0.075 for the mean difference. The registry record does not explain why the reported and recalculated p-values are not identical. The reported analysis and the recalculation should therefore be kept distinct rather than presented as one value.

The recalculation uses the posted means, standard deviations, and group sizes as summary inputs. It is a simple unadjusted comparison and does not reproduce any analysis details that are not reported in the registry record. The sponsor's result is the analysis recorded by the registry; the recalculation is useful as a transparent comparison based on the displayed summaries, but it is not a substitute for a fuller analysis plan or participant-level data.

Both p-values should be interpreted in context with the estimated mean difference of 0.03 and its confidence interval from -0.003 to 0.063. Neither p-value conveys clinical importance, and the registry record reports no threshold for a meaningful difference. It also does not provide information that would resolve the difference between the two p-values, such as additional model details or an explanation of rounding. The trial's own reported analysis is the one attributed to the sponsor; the recalculated result remains explicitly unadjusted.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure and one reported analysis. It reports no secondary posted outcomes. These registry entries describe what is posted, but do not establish that no other outcomes or analyses were considered during study conduct. The registry record does not report a detailed plan for controlling multiplicity, such as whether any adjustment was planned for testing more than one outcome, time point, subgroup, or analysis.

Multiplicity matters in general because conducting multiple statistical tests can increase the chance that at least one result appears unusual by chance. Whether that concern applies, and how it should be handled, depends on the prespecified analysis plan and the family of tests considered. Those details are not reported in the registry record. The single posted primary comparison should not be treated as proof that no other analyses took place.

The record identifies the outcome as umbilical cord pH immediately after delivery and reports means and standard deviations by group. It does not report how missing pH measurements were handled, whether any participants lacked an outcome measurement, or whether exclusions occurred after randomization. The exact analysis population is not reported in the registry record. It is therefore not possible to determine from the posted information whether the analysis was based on all randomized participants or on a subset with available measurements.

The registry record also does not report whether participants were analyzed according to assigned group, how any departures from the assigned procedure were handled, or whether any sensitivity analyses were conducted. These details affect interpretation because the observed comparison can depend on who is included and how incomplete or irregular observations are treated. No assumptions about missingness or adherence should be substituted for information that is not reported in the registry record.

The record does not report an interim analysis plan or stopping rules. It also does not provide a detailed statistical analysis plan that would allow readers to distinguish prespecified analyses from analyses chosen after results were available. The information supports describing the posted primary comparison and its uncertainty, but not a definitive appraisal of multiplicity control, missing-data handling, or analysis-population choices.

15. 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 0% reporting threshold.

The registry reports zero serious adverse events in the severing-cord group and zero in the untouched-cord group. It also reports zero other adverse events in both groups. The groups listed as at risk each contain 30 participants. These figures describe the adverse-event entries in the registry record; they do not establish that no adverse experiences of any kind occurred or that all events were captured.

Death counts are not reported in the registry record. The record does not provide definitions of serious and other adverse events, the period during which events were collected, how events were solicited, or how relatedness to the delivery procedure was assessed. It also does not describe whether any participants were lost to safety follow-up. Without those details, the zero counts should be read narrowly as the posted counts, not as evidence that the procedures carry no risk.

Adverse-event counts are separate from the primary pH outcome. The registry does not report additional safety analyses or descriptions of event types. These data therefore offer limited information about safety, and should not be extended beyond the recorded event categories and group counts.

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

The posted result is a comparison of mean umbilical cord pH immediately after delivery. The severing-cord group mean is 7.29, and the untouched-cord group mean is 7.32. The estimated difference, calculated as untouched minus severing, is 0.03, with a confidence interval from -0.003 to 0.063. The interval includes zero and is compatible with a range of differences around the observed estimate.

This result does not establish that the groups have exactly the same mean. A confidence interval that includes zero can still be compatible with nonzero differences. At the same time, the estimate does not establish that the observed difference is clinically important. The registry record does not report a threshold for interpreting the size of a pH difference, and the posted result concerns only the listed primary outcome.

The sponsor's reported two-sided t-test gives p = 0.1. The unadjusted recalculation gives p = 0.075, and the registry record does not explain their difference. Neither p-value is the probability that a treatment approach is effective or ineffective. The p-values also do not state the likelihood that the observed result will be reproduced in another study.

The record describes randomization, which supports a comparative design, but it does not provide enough detail to assess all aspects of implementation and analysis. It does not report the randomization procedure, allocation concealment, missing outcome handling, analysis population, or a full statistical analysis plan. The summary should therefore be interpreted as evidence about this posted group comparison rather than as a complete account of all possible outcomes or design considerations.

The findings do not answer whether one approach is preferable in clinical practice, and they should not be used as medical advice. They do not address outcomes that are not reported in the registry, nor do they establish the consequences of the procedures in populations or circumstances not described by this trial. The appropriate statistical reading is limited: the posted average pH was higher in the untouched-cord group, while the estimate remains uncertain and its clinical importance is not defined in the record.

17. Why This Trial Matters Statistically

This trial is statistically interesting because it compares two specific procedural approaches using random assignment and a continuous outcome measured immediately after delivery. A mean difference gives a direct summary of how the group averages compare, while the standard deviations and confidence interval help readers consider the variability and uncertainty behind that summary.

The estimate is small in the scale of the reported pH values, but the registry record does not state what magnitude would matter clinically. Statistical interpretation therefore requires separating the numerical estimate from judgments about importance. The confidence interval, from -0.003 to 0.063, includes zero and leaves uncertainty about the direction and size of the underlying difference. This distinction is central to reading small trials: a non-conclusive statistical result is not proof of no effect, and an observed numerical difference is not automatically meaningful.

The trial also illustrates why sponsor analyses and recalculations based on summary statistics need to be identified separately. The registry's reported p-value is 0.1, while an unadjusted recalculation gives 0.075. The record does not explain the difference. Keeping both values attributed to their source makes the analysis more transparent without suggesting that a simple recalculation reproduces unreported analytic details.

Finally, the record makes clear that statistical conclusions depend on more than a p-value. The original sample-size rationale, missing-data handling, analysis population, and multiplicity plans are not reported. Planning illustrations can show how assumptions about target effect size and power relate to participant requirements, but they do not reconstruct the trial's original design or measure observed power. These issues matter when interpreting what a randomized comparison can establish from the information posted.

18. 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 specific to this trial constrain interpretation. The registry record gives two different descriptions of when the cord was cut: the arm description places the procedure after delivery of the anterior shoulder and before extraction of the body, while the brief summary refers to cutting after delivery of the head. The record does not resolve this difference, so the precise procedural timing cannot be established from the descriptions alone.

The posted primary result is limited to umbilical cord pH immediately after delivery. The registry does not report the blood-vessel source of the pH measurement, collection details, or a clinical threshold for meaningful differences. It also reports no secondary outcomes. The result therefore cannot be treated as a broad account of neonatal outcomes.

The registry record does not report the original sample-size justification, detailed randomization methods, allocation concealment, or masking of outcome assessment. Masking is listed as none. Missing-data handling, analysis-population definition, protocol deviations, and interim analyses are also not reported in the registry record. These gaps prevent a full assessment of the risks of bias and the exact analysis choices.

The registry-reported p-value is 0.1, whereas an unadjusted recalculation from posted summary statistics gives p = 0.075. The record does not explain the difference. The confidence interval includes zero, and no clinical-importance threshold is stated. Finally, the adverse-event entries report zero serious and zero other events in both groups, but event definitions and ascertainment details are not reported; death counts are not reported in the registry record. These limitations call for a focused reading of the posted comparison rather than broader conclusions.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Severing Nuchal Cord at the Time of Delivery. — NCT00345254.
• Registry record last updated 2017-05-11; status last verified 2017-04.
• Results first posted 2017-01-10.
• 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.

22. Record Summary

The registry record describes NCT00345254, a completed randomized, parallel-group study sponsored by Wolfson Medical Center. Masking is listed as none, and enrollment is 60. The trial compared intentional severing of an umbilical cord encircling the fetal neck with leaving the cord untouched. The arm descriptions place the procedure after delivery of the anterior shoulder and before extraction of the body, while the brief summary gives a differing timing description.

The primary outcome was umbilical cord pH immediately after delivery. The group means were 7.29 for severing and 7.32 for untouched cord. The posted mean difference, untouched minus severing, was 0.03, with a confidence interval from -0.003 to 0.063. The sponsor-reported two-sided t-test gives p = 0.1; the unadjusted recalculation gives p = 0.075. No secondary outcomes are posted. The record reports zero serious and zero other adverse events in both groups; death counts are not reported in the registry record.

Details of the original sample-size rationale, missing-data handling, analysis population, and full statistical plan are not reported in the registry record.