Paracervical Block Versus No Paracervical Block During IUD Insertion: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Paracervical Block Versus No Paracervical Block During IUD Insertion (NCT02904915), a randomized phase 4 study. The primary outcome is Pain Score as Assessed by a Visual Analogue Scale (VAS).

2. Clinical Question

The clinical question is framed around a patient-reported pain measure in the setting of IUD insertion. The registry’s study summary also refers broadly to pain and discomfort, but the primary outcome detailed in the record is the pain score at the baseline assessment, about 30 seconds after insertion of the speculum. The recorded sequence includes later pain assessments after tenaculum placement and after IUD insertion; those time points should not be confused with the primary outcome’s stated timeframe.

The registry describes a randomized comparison, with one group receiving a paracervical block and the other receiving no analgesia. It does not report a separate estimate for discomfort in the information available for this analysis. Nor does the primary endpoint establish whether pain differed at the later procedural steps, or how scores changed over time. Those questions require results for the relevant outcomes and assessment times, which are not reported in the registry record.

3. Trial Design

This was a phase 4, randomized, parallel-group trial with no masking, listed as completed. The registry reports enrollment of 50 participants. Its two intervention descriptions are IUD placement with a paracervical block using 1% lidocaine and IUD placement with no analgesia. The listed sponsor is The University of Texas Health Science Center, Houston.

The registry gives a start date of 2017-01-12 and a primary completion date of 2017-10-09. It describes the intended setting as University of Texas Physicians clinics where women presented for IUD insertion. The record does not report further details about eligibility criteria, recruitment procedures, or how random assignment was generated or concealed. The randomization method and allocation concealment are therefore not reported in the registry record.

No masking was used. Because pain was assessed by a visual analogue scale, the outcome is a participant-reported score, and the record does not describe masking of participants or other people involved in assessment. This design feature is relevant when interpreting a subjective outcome, although the record does not establish whether it affected responses.

The primary outcome is a mean pain score at the assessment about 30 seconds after speculum insertion. The registry describes a procedural sequence that also includes subsequent pain assessments after tenaculum placement and after IUD insertion. It lists three outcome measures, but secondary results are not posted in the record. Details of the original sample-size justification, the planned analysis population, and the trial’s complete statistical analysis plan 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.

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 Pain Score as Assessed by a Visual Analogue Scale (VAS), measured over baseline (about 30 seconds after insertion of the speculum).

The primary endpoint is the mean pain score on the Faces pain visual analogue scale, assessed about 30 seconds after insertion of the speculum. The scale ranges from 0, described as very happy or no hurt, to 10, described as hurting as much as can be imagined. The registry reports the arm-level results as means with standard deviations.

A continuous scale retains gradations in reported pain rather than reducing responses to categories such as pain present or absent. Comparing group means gives a summary of the average score in each randomized group at the specified assessment. The standard deviation describes how much scores varied among participants within each group; it is not the uncertainty around the group mean.

In general, a participant-reported pain scale is used to capture an experience that may not be represented fully by a clinical observation alone. The score is tied to the timing and wording of the assessment. Here, the primary timeframe is the assessment after speculum insertion, before the later steps described in the procedural sequence. It should therefore be interpreted as a score at that point, not as an overall pain score for the entire IUD insertion procedure.

The registry lists the endpoint’s scale and timing, but does not report a minimal important difference or a threshold for interpreting an individual score. It also does not post the later time-point results in the record. The scale can describe reported pain, but these registry entries alone do not establish how participants valued a particular difference in score.

7. Results Posted in the Registry

• No Analgesia: mean 2.10 versus 2.40 on control; difference -0.30 (95% CI -1.60 to 1.00), standardized effect d = -0.13; z-test p = 0.652.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry presents a continuous pain outcome as a mean and standard deviation for each group. A separate simple, unadjusted re-calculation compares the group means and gives a mean difference, confidence interval, and p-value. These are different ways of describing the same continuous-outcome comparison: the group summaries describe each arm, while the difference describes their contrast.

What does the mean difference represent?

The re-calculated contrast is defined as the no-analgesia mean minus the paracervical-block mean. The estimate is -0.3 units. With this direction, a negative value means the posted average score is lower in the no-analgesia group; a positive value would mean it is higher. The sign depends on the stated subtraction order, so the direction should always be read alongside the group labels. The means are 2.1 for no analgesia and 2.4 for paracervical block.

The contrast is unadjusted: it is calculated from the posted group summaries and does not account for other variables. The registry record does not describe an adjusted model for this primary outcome. An unadjusted comparison is not automatically inappropriate, but it answers a particular question: how the reported group averages differ without covariate adjustment in that calculation.

What does the standard deviation describe?

In general, a standard deviation describes the dispersion of individual observations around a group mean. Larger dispersion means that observations are more spread out, while smaller dispersion means they cluster more closely around the mean. Here, the reported standard deviations are 2.3 and 2.4. They describe variability in pain scores, not uncertainty in the estimated means and not the precision of the between-group contrast.

The re-calculation uses the posted continuous summaries, including the arm sizes and standard deviations. It does not create additional participant-level information or account for details that are absent from those summaries. The registry does not provide participant-level scores, so alternative models or checks that require those data cannot be evaluated from the posted information.

How should the confidence interval be read?

In general, a confidence interval gives a range of values compatible with the data and the calculation’s assumptions, expressing uncertainty around an estimate. For the mean difference, the reported interval runs from -1.603 to 1.003 units. Because it crosses zero, it includes no difference as well as values on either side of zero. It therefore does not isolate a single direction of difference with high precision.

A confidence interval is not a statement that a particular range of individual scores contains a specified share of participants. It concerns uncertainty in the estimated group contrast. Nor does the interval assign probabilities to each value within its limits. Its interpretation depends on the method and assumptions used to calculate it.

What does the p-value say?

In general, a p-value describes how unusual data at least as inconsistent with a null hypothesis would be under that hypothesis and the statistical model. It is not the probability that the null hypothesis is true, and it does not measure the clinical importance of a difference. The unadjusted re-calculated p-value is 0.652. Read together with the estimate and interval, it indicates that this calculation does not provide a precise distinction between the groups at the specified assessment.

The registry separately reports a Fisher Exact analysis with p = 0.59. Fisher Exact is a method for categorical data, whereas the re-calculation uses the continuous means. The registry entry does not identify the parameter or outcome values used for that sponsor analysis, so its result cannot be reconstructed from the information reported. No further detail about the sponsor’s statistical model or test assumptions is reported in the registry record.

Why can spread matter?

In general, greater variability makes a group contrast harder to estimate precisely when other design features are held constant. If a continuous outcome has more spread, the observed scores may be less informative about a small difference in group averages. Some outcomes can also show over-dispersion, meaning their variability exceeds what a simple model assumes. In such cases, a model that allows for the extra variability may be needed. The registry does not report an over-dispersion assessment or a model for this endpoint, and the posted summaries alone do not establish that over-dispersion is present.

All re-calculated statistics are simple, unadjusted calculations from the registry’s summary values. They should be distinguished from the sponsor’s reported analysis, whose stated method and p-value are recorded separately. The registry does not provide enough detail to establish that the sponsor analysis tested the same contrast at the same assessment time.

10. Confidence Intervals and Precision

The mean difference is -0.3 units, with a confidence interval from -1.603 to 1.003. This interval is wide enough to include a lower mean score in either group, as well as zero difference. The point estimate alone gives the most compact summary of the observed contrast, but the interval shows that the estimate is uncertain and does not pinpoint the direction or size of a difference.

In general, a confidence interval conveys precision as well as direction. A narrower interval would indicate a more precisely estimated contrast under the calculation’s assumptions; a wider interval indicates more uncertainty. The reported interval should be interpreted in the scale’s units, not as a range of individual participants’ pain scores. It concerns the mean difference between groups at the specified assessment.

The arm-level standard deviations are 2.3 for paracervical block and 2.4 for no analgesia, while each arm has 25 participants in the posted summaries. The spread of scores relative to the estimated contrast helps explain why a modest point estimate can remain uncertain. The registry’s record does not include participant-level data or additional interval estimates for the later pain assessments.

The interval is not evidence of equivalence. A conclusion of equivalence would require a defined margin and an analysis designed to test whether the plausible difference lies within that margin. Such a margin is not reported in the registry record. The sponsor’s Fisher Exact result also has no confidence interval or effect estimate posted, limiting assessment of its precision.

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. They are illustrations based on the observed effect rather than the trial’s original design assumptions. The registry record does not report the original sample-size justification or its assumptions.

The planning calculation assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It sets the effect to detect as a stated fraction of the observed effect. For planning at 100% of the observed effect, the displayed requirement is 964 participants per arm for 80% power and 1,291 participants per arm for 90% power. For planning at 75% of the observed effect, the figures are 1,714 participants per arm for 80% power and 2,294 participants per arm for 90% power. For planning at 50% of the observed effect, they are 3,855 participants per arm for 80% power and 5,161 participants per arm for 90% power.

In plain terms, the 80% power column gives the planned number per arm for a design intended to have an 80% chance of detecting the specified effect under the stated assumptions if that effect is real. The 90% power column describes the corresponding planning target for a 90% chance. These are design calculations, not guarantees about a future study’s results. The values are not observed power for this completed trial.

The pattern reflects a general planning principle: smaller effects are harder to distinguish from random variation, so detecting them requires more participants when other assumptions remain the same. These figures are illustrations based on the observed estimate and should not be read as a justified recommendation for a future trial. The record does not report a minimal important difference, and the planning calculation does not establish what effect would be meaningful to patients or clinicians.

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 = -0.300; pooled standard deviation σ = 2.351.
2. n = 2 × (1.96 + 0.842)² × 2.351² / -0.300² = 963.7, rounded up to 964 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 <- -0.3                      # observed difference in means
sigma <- 2.35053185470863                     # 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(2904915)
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 = 964 (80% power), 1,291 (90% power)
 75% of observed effect: n per arm = 1,714 (80% power), 2,294 (90% power)
 50% of observed effect: n per arm = 3,855 (80% power), 5,161 (90% power)
power.t.test: 964.6 
Simulated power at n = 964 per arm: 0.799 (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 a sponsor analysis using Fisher Exact and gives p = 0.59. It does not report an effect estimate, confidence interval, or test-specific outcome values for that entry. The statistical meaning of the sponsor’s p-value therefore cannot be fully assessed from the registry record alone.

The unadjusted re-calculation uses the posted continuous group means and standard deviations. It estimates a mean difference of -0.3 units, with a confidence interval from -1.603 to 1.003 and p = 0.652. These calculations describe a difference between average pain scores. Fisher Exact is identified as the method for the sponsor analysis, so its reported p-value should not be treated as a direct reproduction of the continuous mean comparison.

The registry record does not explain whether the sponsor analysis addressed the same endpoint, assessment time, or contrast as the re-calculation, or why the methods differ. The two p-values should therefore be reported with their respective methods rather than combined or interpreted as though they were identical tests. No sponsor effect estimate is available for a direct comparison of magnitudes.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures, while the number of posted secondary outcomes is 0. It also indicates three analyses, but the record does not report enough detail about all analyses, their relationship to the outcome measures, or which were designated primary or secondary beyond the primary endpoint described. The reported analysis entry identifies Fisher Exact with p = 0.59, but gives no estimate or confidence interval.

When a study examines multiple outcomes, assessment times, or statistical comparisons, the chance of finding at least one apparently notable result can increase. In general, multiplicity procedures or a prespecified hierarchy can help govern interpretation across multiple tests. The registry record does not report a multiplicity adjustment, testing hierarchy, or detailed plan for handling multiple comparisons. The posted information therefore does not establish whether or how multiplicity was addressed.

The record does not report how missing pain scores were handled, whether any participants lacked outcome data, or whether an imputation method was used. It also does not identify the analysis population, such as whether the primary analysis followed randomized assignment or included only participants with recorded scores. These details are not reported in the registry record, so the completeness and population basis of the summaries cannot be independently evaluated from the posted entries.

The original statistical analysis plan, sample-size justification, interim-analysis plan, and details of any protocol deviations are not reported in the registry record. Their absence from the registry entries does not demonstrate that such procedures were or were not used; it means their role cannot be assessed from this record.

15. 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 reports 0 serious adverse events among 25 participants at risk in the paracervical-block group and 0 among 25 participants at risk in the no-analgesia group. It also reports 0 other adverse events in each group. No serious adverse-event terms are listed.

These entries mean that no events in the reported categories were recorded in the registry for the listed groups. They do not show that no adverse events of any kind occurred outside the categories or reporting period represented in the record. The registry does not provide further details about adverse-event definitions, the duration of safety follow-up, or the method used to collect events.

Zero reported events in groups of the posted size cannot establish that the risk of an event is absent. The figures are descriptive safety information for this trial record, not a guarantee about risk in other patients or settings.

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

The posted primary summaries show mean pain scores of 2.4 with paracervical block and 2.1 with no analgesia at the assessment about 30 seconds after speculum insertion. The unadjusted mean difference, defined as no analgesia minus paracervical block, is -0.3 units. Its confidence interval, -1.603 to 1.003, spans zero and values in both directions. The data therefore do not provide a precise estimate of the direction or size of the difference at this assessment.

This result does not establish equivalence between the approaches. Equivalence requires a prespecified margin and a suitable analysis, neither of which is reported in the registry record. A p-value that is not small does not prove that there is no difference, and the point estimate does not establish a clinically meaningful difference. The registry does not report a threshold for meaningful change on this scale.

The result is specific to the primary assessment after speculum insertion. The procedural description includes later pain assessments after tenaculum placement and IUD insertion, but their outcome results are not reported in the registry record. The result therefore cannot be used to infer the comparative pain scores at those later points or across the full procedure.

The findings also do not answer every question in the broad study summary, which refers to pain and discomfort. The primary result concerns a defined pain score, not a separately reported discomfort outcome. The record does not provide enough detail to assess missing scores, the analysis population, or the sponsor analysis’s relationship to this continuous comparison.

More generally, the posted results describe the observed trial data and their uncertainty. They do not establish what any individual will experience, and they should not be extended beyond the population and setting described without supporting evidence. The record’s limited eligibility and follow-up details further constrain broader interpretation.

17. Why This Trial Matters Statistically

This trial illustrates why a group comparison should be read through both its estimate and its uncertainty. The mean difference is small in the scale’s units, but the confidence interval ranges across zero and values favoring either direction under the defined subtraction order. Reporting only the point estimate or only a p-value would leave out important information about precision.

It also illustrates the distinction between within-group spread and uncertainty about a between-group contrast. The standard deviations describe variation in participants’ pain scores, while the confidence interval describes uncertainty in the estimated mean difference. These quantities answer related but different questions and should not be substituted for one another.

The endpoint’s timing matters. Pain was assessed at several procedural steps according to the registry’s description, but the primary outcome refers to the assessment after speculum insertion. A result at that time point is not automatically a summary of pain during later steps. Clear interpretation depends on matching each estimate to its measurement and timing.

Finally, the record juxtaposes a continuous-outcome re-calculation with a sponsor analysis identified as Fisher Exact. Without an effect estimate or further method details for the sponsor entry, those results cannot be reconciled fully. This highlights the value of reporting the analysis method, outcome definition, effect estimate, and confidence interval together. The trial is statistically informative as an example of why design details and transparent reporting shape what conclusions can be drawn from a result.

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.

The posted enrollment is 50, with 25 participants in each arm’s outcome summary. The small amount of information available for estimating a continuous group difference is reflected in the confidence interval, which includes values on either side of zero. The record does not report an original sample-size justification, so it is not possible to assess the precision the trial was designed to achieve.

The study was unmasked. Because the endpoint is a participant-reported pain score, expectations or awareness of the assigned approach could potentially influence reporting in general. The registry does not show whether any such influence occurred. The record also does not describe masking of those collecting or analyzing the outcome.

The registry’s primary timeframe is a single assessment about 30 seconds after speculum insertion, while the procedural description includes later assessments. Results for those later assessments are not posted, and secondary outcomes are not reported. This limits interpretation to the specified primary assessment rather than pain over the entire procedure.

Eligibility criteria, participant characteristics, outcome completion, missing-data handling, and analysis-population details are not reported in the registry record. The sponsor’s Fisher Exact entry also lacks an effect estimate and confidence interval, and its relationship to the continuous primary comparison is not explained. These reporting gaps limit evaluation of generalizability, analysis decisions, and the full context of the posted result.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Paracervical Block Versus No Paracervical Block During IUD Insertion — NCT02904915.
• Registry record last updated 2018-11-07; status last verified 2018-10.
• Results first posted 2018-11-07.
• 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 describes a completed, phase 4, randomized, parallel-group trial without masking, comparing paracervical block with 1% lidocaine against no analgesia during IUD placement. Enrollment was 50. The listed start date is 2017-01-12, and the primary completion date is 2017-10-09.

The primary endpoint is the mean Faces pain visual analogue scale score about 30 seconds after speculum insertion. The posted means are 2.4 for paracervical block and 2.1 for no analgesia. The unadjusted re-calculated mean difference is -0.3, with a confidence interval from -1.603 to 1.003 and p = 0.652. The sponsor analysis is listed as Fisher Exact with p = 0.59.

No serious adverse events or other adverse events are reported in either group. Further details about eligibility, missing data, analysis populations, and the original sample-size assumptions are not reported in the registry record.