Laminaria Compared to Dilapan-S for Cervical Preparation Before Dilation and Evacuation at 18-24 Weeks of Gestation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Laminaria Compared to Dilapan-S for Cervical Preparation Before Dilation and Evacuation at 18-24 Weeks of Gestation (NCT02033083), a randomized na study. The primary outcome is D&E Procedure Time.

2. Clinical Question

3. Trial Design

The registry describes a randomized, triple-masked, parallel-group trial with an enrollment of 180. It lists the phase as not applicable. The condition is second-trimester abortion, and the trial title specifies cervical preparation before dilation and evacuation at 18-24 weeks of gestation. The record identifies Planned Parenthood of Greater New York as the sponsor and marks the study completed.

Participants were allocated to laminaria or Dilapan-S. In both arms, the cervical dilators were placed one day before the dilation and evacuation procedure. The comparison therefore concerns two forms of overnight cervical preparation, with procedure time assessed on the day of the procedure. The registry identifies the primary outcome as length of the procedure in minutes.

The registry labels the study triple-masked, but it does not identify which groups of people were masked or describe how masking was maintained. The method used to generate or conceal the random allocation is not reported in the registry record. Further details of the treatment procedures, including how many dilators were placed or how placement was standardized, are not reported in the registry record.

The record gives start and primary-completion dates of 2013-12 and 2016-02, respectively. It includes primary outcome summaries for both groups, but no secondary outcome results are posted. The registry record lists zero analyses. That does not establish that no analyses were conducted; it means that analyses are not listed in the record. The original study's sample-size justification and detailed 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.

Before assignment: If eligible for study participation, the member of the research team will review study procedures and the risks and benefits of participation with the patient, and obtain informed consent for study participation. Once informed consent is obtained, participants will be assigned a screening number. Research staff will then administer a verbal 10-minute survey (Form 1) to collect demographic information and assess baseline pain, bleeding, nausea and other pregnancy-related symptoms.

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 D&E Procedure Time, measured over The primary outcome measure will be assessed on the day of the patient's D&E procedure. (day 2).

The primary endpoint is dilation and evacuation procedure time, measured in minutes on the day of the procedure. It represents the length of the procedure, rather than the time spent placing cervical dilators or the duration of cervical preparation. In this trial, the endpoint was used to compare procedure time after overnight preparation with laminaria or Dilapan-S.

Procedure time is a continuous measure: it can take many values along a scale, rather than being limited to a yes-or-no outcome. The registry reports the mean and standard deviation for each arm. The mean describes the average procedure time in the posted group summary. The standard deviation describes how much individual procedure times varied around that mean; it is not the uncertainty in the mean itself.

The reported arm means are 7.35 minutes for laminaria and 7.55 minutes for Dilapan-S. These summaries make it possible to describe the observed group averages and to calculate an unadjusted difference with an interval expressing uncertainty. They do not by themselves describe the distribution of procedure times, identify reasons for individual variation, or show whether the comparison was adjusted for other participant or procedure characteristics.

The registry also lists several secondary objectives, including cervical dilation, use and ease of mechanical dilation, number of dilators placed, completion without further preparation, complications, pain and other side effects, and patient and provider acceptability. Results for those outcomes are not reported in the registry record. Consequently, the primary endpoint addresses procedure duration, but the posted results do not provide findings for the other listed questions.

7. Results Posted in the Registry

• Dilapan-S: mean 7.55 versus 7.35 on control; difference 0.20 (95% CI -1.02 to 1.42), standardized effect d = 0.05; z-test p = 0.749.

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical comparison concerns a continuous endpoint measured in minutes. For each randomized arm, the registry reports a mean and a standard deviation. A mean difference expresses how far apart the group averages are on the original measurement scale. The recalculated estimate uses Dilapan-S minus laminaria, so positive values indicate a higher mean in the Dilapan-S group and negative values indicate a lower mean in that group. The estimate is 0.2 minutes.

What does the confidence interval describe?

A confidence interval is a range of values generated by a statistical procedure to represent uncertainty about an estimated quantity. For this comparison, it is an interval for the difference between group means, not a range containing a stated proportion of individual procedure times. The interval extends from -1.023 to 1.423 minutes. Because it crosses zero, the summaries do not distinguish confidently between a lower mean, no mean difference, or a higher mean for Dilapan-S under this unadjusted calculation. The interval also shows the scale of uncertainty: the observed estimate is not precise enough to pin the difference to a narrow value.

The interval is calculated from the posted means, standard deviations, and sample counts using an unadjusted comparison. It does not incorporate covariate adjustment, clustering, or other modeling details. The registry does not report the trial's own analysis method, so the recalculation should not be confused with an analysis performed or selected by the investigators. If the registry record contained a discrepancy between sponsor-reported and recalculated results, the sponsor's analysis would take precedence; no such discrepancy is flagged for this record.

What does the p-value add?

The unadjusted p-value is 0.749. In general, a p-value describes how compatible data at least as extreme as those observed are with a specified null hypothesis, under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. Here, the p-value is consistent with the uncertainty visible in the confidence interval. It should not be used alone to declare the preparations equivalent or to conclude that no difference exists.

Standard deviations and standard errors have different roles. A standard deviation describes dispersion of participant-level measurements around an arm mean. The registry summaries report standard deviations of 3.63 minutes for laminaria and 4.59 minutes for Dilapan-S. A standard error, by contrast, concerns the precision of an estimate such as a mean. The recalculation includes arm-level standard errors of 0.387 and 0.489 minutes. Neither measure describes the full range of individual procedure times, and neither should be interpreted as a treatment effect.

Why can over-dispersion matter?

As a general statistical point, over-dispersion means that observed variability is greater than a statistical model expects. When a model understates variability, standard errors can be too small and confidence intervals can be too narrow, making results appear more precise than they are. This concern is especially relevant to count or binary outcomes analyzed with models that impose a particular variance structure. The primary endpoint is continuous, and the registry provides arm-specific standard deviations, but it does not report diagnostics or a model assessment. Over-dispersion is not reported as a finding in this trial, and the posted record does not allow a diagnostic assessment.

The sample-size illustrations use a normal approximation and equal allocation, with a two-sided significance level of 0.05. They use fractions of the observed effect as planning targets. In general, planning calculations depend on assumptions about the effect to detect, variability, significance threshold, allocation, and analysis method. These illustrations use the assumptions stated in the registry's planning material, but those assumptions are not evidence of the original trial design. The original sample-size rationale, target effect, anticipated variability, and any allowance for missing outcomes are not reported in the registry record.

The randomized design is relevant to interpreting the group comparison because random allocation is intended to balance factors between groups on average. However, the registry does not report allocation-generation or concealment details, and the posted recalculation does not adjust for participant characteristics. The trial is labeled triple-masked, but the people masked and the practical masking procedures are not reported in the registry record. These omissions limit assessment of how the trial was implemented and analyzed.

The primary outcome summaries and recalculation provide a focused comparison of average procedure time. They do not reveal the shape of the outcome distributions, possible outliers, missing outcome patterns, or whether all randomized participants were included in the reported means. Those details, along with the prespecified analysis population, handling of missing observations, and any planned sensitivity analyses, are not reported in the registry record. The results should therefore be read as summary-statistic evidence, not as a complete reconstruction of the trial's statistical analysis.

10. Confidence Intervals and Precision

The unadjusted recalculated mean difference is 0.2 minutes, with a confidence interval from -1.023 to 1.423 minutes. This interval expresses uncertainty about the difference between the arm means. It spans zero and includes values in both directions, so the estimate does not locate the underlying difference precisely on one side of zero. The range should not be read as a prediction interval for an individual patient's procedure time.

The observed means are 7.35 minutes for laminaria and 7.55 minutes for Dilapan-S, while the arm standard deviations are 3.63 and 4.59 minutes, respectively. The standard deviations indicate variability in procedure times among participants. The confidence interval instead reflects uncertainty around the estimated difference between averages. The width of the interval is important alongside the point estimate: a small estimated difference does not, by itself, mean that the true difference is known to be small.

Precision depends on the amount of information in the data and on variability. The primary summaries include 88.0 participants in each arm. The registry does not report whether those counts reflect all randomized participants, how missing outcome data were handled, or whether the interval was part of a prespecified analysis. Those uncertainties matter when assessing how fully the interval represents the trial's intended analysis.

No threshold for a clinically important difference in procedure time is reported in the registry record. Statistical uncertainty can therefore be described, but the interval cannot be classified against a trial-defined threshold for clinical importance. The posted results are most appropriately read as showing a modest difference between observed averages with substantial uncertainty about the direction and size of the underlying difference.

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 apply to a continuous outcome and are illustrations based on the observed effect, using the stated fractions of that effect. 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 the stated fraction of the observed effect. The assumptions used for the trial's original design are not reported in the registry record.

The 80% power column describes the number of participants per arm estimated, under these assumptions, to give an 80% chance of detecting the specified effect if that effect is present. The 90% power column gives the corresponding planning number for a 90% chance. These are prospective planning quantities, not descriptions of the trial's achieved probability of finding a result. This is not observed power.

Each row changes the effect size used in the planning illustration: the calculations consider 100%, 75%, and 50% of the observed effect. A smaller effect is harder to distinguish from random variation, so more participants are needed to detect it at the same significance level and planned power. The posted participant counts rise as the assumed effect becomes smaller. The large values should not be read as a recommendation for a future study or as the number needed to interpret the current trial; they are conditional on the stated assumptions and the observed effect used for the illustration.

Because the observed mean difference is small relative to the variability in procedure time, planning around a fraction of that observed difference produces large participant requirements. Such calculations can be sensitive to the estimated effect, especially when it comes from a trial with limited outcome counts. The registry record does not report the original target effect, sample-size method, or design rationale, so these illustrations cannot establish whether the completed trial met its own planned enrollment target.

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 = 0.200; pooled standard deviation σ = 4.138.
2. n = 2 × (1.96 + 0.842)² × 4.138² / 0.200² = 6,719.6, rounded up to 6,720 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 <- 0.2                      # observed difference in means
sigma <- 4.13793426724012                     # 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(2033083)
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 = 6,720 (80% power), 8,996 (90% power)
 75% of observed effect: n per arm = 11,946 (80% power), 15,993 (90% power)
 50% of observed effect: n per arm = 26,879 (80% power), 35,983 (90% power)
power.t.test: 6720.6 
Simulated power at n = 6,720 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. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure and zero analyses. It identifies several secondary objectives in the study summary, but secondary outcome results are not reported in the registry record. The record therefore does not allow a reader to see whether those outcomes were analyzed, how many comparisons were made, or whether results were selected for posting.

Multiplicity arises when many outcomes, treatment contrasts, or subgroup comparisons are examined. In general, the more statistical tests conducted, the greater the chance that some results may appear notable by chance. Researchers may address this through prespecified outcome hierarchies, adjustment procedures, or clearly defined exploratory analyses. Any multiplicity procedure, hierarchy, or distinction between confirmatory and exploratory analyses is not reported in the registry record. The posted unadjusted p-value is not described as adjusted for multiple comparisons.

The registry does not report how missing primary outcome observations were handled, whether any imputation was used, or whether sensitivity analyses were conducted. The primary outcome summaries include 88.0 participants per arm, whereas the enrollment is 180. The record does not explain the relationship between these counts, so no reason for the difference can be inferred. The counts alone do not establish whether participants were excluded, outcomes were missing, or a different analysis population was used.

The analysis population is not reported in the registry record. In particular, the record does not say whether the primary comparison followed an intention-to-treat approach, included participants according to treatment received, or used another defined population. The allocation is described as randomized, but the posted summary does not establish how deviations from assigned preparation, if any, were handled.

These gaps affect the interpretation of both the effect estimate and its uncertainty. If outcome availability or analysis-set membership differed from the randomized groups, the reported summaries might not represent the full randomized comparison. That possibility is not evidence that such differences occurred; the registry record does not provide enough information to assess it. A complete account of missingness, analysis populations, multiplicity handling, and the prespecified statistical plan is not reported in the registry 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 0% reporting threshold.

The registry safety summary lists 89 participants at risk for serious adverse events in the laminaria group and 89 in the Dilapan-S group. It records zero participants affected by serious adverse events in either group. For other adverse events, it also lists 89 at risk in each group and zero participants affected in each group.

These entries mean that the posted registry summary reports no affected participants in the listed categories among the stated risk groups. They do not prove that no adverse events of any kind occurred or provide detail about event definitions, collection methods, duration of follow-up, or severity categories beyond the serious-versus-other distinction. The death entries are not reported in the registry record.

The safety risk counts differ from the primary outcome counts of 88.0 participants in each arm. The registry record does not explain that difference, so the counts should be kept distinct rather than treated as interchangeable. The summary also does not provide event narratives or additional safety analyses. It is a concise registry report, not a full account of safety monitoring or all clinical outcomes.

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

The posted primary outcome describes average dilation and evacuation procedure time after overnight cervical preparation with laminaria or Dilapan-S. The means are 7.35 minutes and 7.55 minutes, respectively. The unadjusted recalculated difference is 0.2 minutes, with a confidence interval from -1.023 to 1.423 minutes. These statistics describe the observed group summaries and the uncertainty around their difference.

The result does not establish that the two preparations produce equivalent procedure times. A nonsignificant unadjusted p-value of 0.749 is not proof of equality, and the confidence interval includes differences in either direction. The interval also does not tell whether any value within it would matter clinically; a threshold for clinical importance is not reported in the registry record.

The trial's stated hypothesis was that procedure time would be less with Dilapan-S. The posted mean is slightly higher in the Dilapan-S group, but the estimate is uncertain and the registry does not provide an adjusted sponsor analysis. The result should not be converted into a conclusion about treatment effectiveness or an individual clinical decision. It is a comparison of one recorded endpoint in the posted group summaries.

The record also does not report results for the listed secondary questions about cervical dilation, mechanical dilation, dilator number, completion without further preparation, complications, pain and other side effects, or acceptability. The safety summary records zero serious and other affected participants in each group among 89 at risk, while deaths are not reported in the registry record. These entries do not substitute for the missing secondary results or a detailed safety account.

In practical statistical terms, the result is informative about the scale of the observed averages, but not decisive about the underlying difference. Its meaning is bounded by the outcome counts, the width of the confidence interval, and the lack of detail about analysis methods, missing outcomes, and the original statistical plan. It supports neither a claim of equivalence nor a claim that a meaningful difference has been ruled out.

16. Why This Trial Matters Statistically

This trial illustrates why a point estimate should be read together with its uncertainty. The arm means are close, and the recalculated mean difference is 0.2 minutes, but the confidence interval extends to values on either side of zero. Looking only at the difference or only at the p-value would conceal how uncertain the comparison remains.

It also shows the distinction between within-group variability and precision of a treatment contrast. The standard deviations describe variation in procedure time among participants. The confidence interval describes uncertainty in the difference between arm means. A reader needs both kinds of information to understand what the posted summaries do and do not establish.

The registry also gives a useful example of the limits of planning calculations based on an observed effect. The illustrations translate different fractions of that effect into participant requirements under stated assumptions. Smaller target effects require more participants. But those calculations are not the original trial's design rationale, and they do not describe the probability that this completed trial would detect a result.

Finally, the distinction between a registry summary and a full statistical report matters. The record identifies randomization and triple masking, yet does not provide details of allocation procedures, masking roles, missing-data handling, or the analysis population. It reports the primary outcome but no secondary results. Statistical interpretation depends not only on the numerical estimate, but also on how outcomes were collected and analyzed and how completely those decisions are documented.

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.

The registry record gives limited information about how the trial was conducted and analyzed. Although it labels the study randomized and triple-masked, the randomization method, allocation concealment, and identities of the masked groups are not reported in the registry record. Those details would help readers assess the protection against selection and measurement biases.

The primary summaries include 88.0 participants in each arm, while the registry reports enrollment of 180. The safety summaries list 89 participants at risk in each arm. The record does not explain the different counts or identify the primary outcome analysis population. It also does not report missing-data handling, participant flow, protocol deviations, or sensitivity analyses. No explanation should be inferred from the counts alone.

Only the primary endpoint is reported. The study summary lists secondary aims concerning cervical dilation, mechanical dilation, number of dilators, further preparation, complications, pain and side effects, and acceptability, but those findings are not reported in the registry record. This limits the ability to assess the broader set of questions the trial was designed to address.

The posted comparison is an unadjusted recalculation from summary statistics, not a reported sponsor analysis. The registry record does not provide an analysis plan, a justification for the original sample size, a clinically important difference threshold, or a description of outcome distributions. It is therefore not possible from this record to assess whether the posted comparison matches the planned analysis or whether the trial was designed to detect a particular effect.

The adverse-event summary reports zero affected participants for the listed categories, but deaths are not reported in the registry record. Event definitions, follow-up details, and more complete safety findings are also not reported. These limitations do not show that problems occurred; they define what the posted record can support.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Laminaria Compared to Dilapan-S for Cervical Preparation Before Dilation and Evacuation at 18-24 Weeks of Gestation — NCT02033083.
• Registry record last updated 2021-07-12; status last verified 2021-06.
• Results first posted 2018-09-12.
• 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

NCT02033083 is a completed randomized, triple-masked, parallel-group trial sponsored by Planned Parenthood of Greater New York. It enrolled 180 participants and compared laminaria with Dilapan-S for cervical preparation one day before dilation and evacuation at 18-24 weeks of gestation.

The primary outcome was procedure time in minutes, assessed on the day of the procedure. The registry summaries report means of 7.35 minutes for laminaria and 7.55 minutes for Dilapan-S, with standard deviations of 3.63 and 4.59 minutes. The unadjusted recalculated mean difference is 0.2 minutes, with a confidence interval from -1.023 to 1.423 minutes and an unadjusted p-value of 0.749.

The record does not report secondary outcome results, the trial's detailed analysis plan, missing-data handling, or the original sample-size justification. Safety summaries record zero serious and zero other affected participants in each group among 89 at risk; deaths are not reported in the registry record.