Histerectomy Vs Partial Myometrial Resection for Placenta Accreta Spectrum: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Histerectomy Vs Partial Myometrial Resection for Placenta Accreta Spectrum (NCT05013749), a randomized na study. The primary outcome is Screening Failure Percentage.

2. Clinical Question

3. Trial Design

NCT05013749 is a completed randomized, parallel-group feasibility study comparing hysterectomy with partial myometrial resection for placenta accreta spectrum. The registry lists the phase as NA and the masking as none. It identifies Fundacion Clinica Valle del Lili as sponsor. The study record gives an enrollment of 60 and describes an intended multicenter randomized trial across 3 health institutions. The record does not provide site-specific enrollment or outcomes.

The study description says that eligible participants would sign informed consent, proceed to surgery, and be randomized to one of the procedures before the procedure began. The planned follow-up included the immediate post-surgical period (72 hours), 7 to 12 days, and 42 days postpartum. The primary endpoint was assessed during surgery. The posted secondary outcomes include maternal death, intra-surgical bleeding volume, transfusion measures, near-miss criteria, bladder injury, reoperation, and intensive care admission.

The registry marks the study completed. Its start date is 2021-08-20 and its primary completion date is 2023-04-17. The study description characterizes it as a feasibility study, rather than reporting it as a definitive evaluation of comparative clinical outcomes. The planned enrollment and duration in the description are design information; they do not establish that all planned procedures or follow-up assessments occurred as intended. Reasons for any departures from the plan, participant flow, and site-level implementation details are not reported in the registry record.

The registry record contains outcome counts for the primary endpoint and some secondary outcomes, but reports no sponsor statistical analyses. It does not report how randomization was generated or concealed, whether outcome assessors were blinded, or which analysis population was intended. Those details should not be inferred from the randomized, unmasked designation.

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

Reasons for not completing this period:

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 Screening Failure Percentage, measured over During surgery.

The primary endpoint, Screening Failure Percentage, is defined as the percentage of participants who entered the study but did not have macroscopic findings of placenta accreta spectrum during laparotomy. It was assessed during surgery. In practical terms, it captures whether the suspected condition was visibly confirmed at the time of the operation among those who had entered the study.

The registry reports counts for this endpoint: 7 participants in the hysterectomy group and 2 in the partial myometrial resection group. The corresponding group sizes are 31 and 29. The endpoint title refers to a percentage, but the posted group results are participant counts; no separate percentage estimates are reported as the primary outcome values. The unadjusted recalculated risk difference is -0.157 for partial myometrial resection relative to hysterectomy, with an interval from -0.331 to 0.017.

This endpoint is useful in a feasibility study because it describes how often the suspected diagnosis was not confirmed at laparotomy, an issue relevant to recruiting and conducting a trial of procedures for placenta accreta spectrum. It should not be interpreted as a direct comparison of surgical success or as an outcome among only participants whose diagnosis was confirmed. The registry record does not report a separate analysis restricted to confirmed cases.

7. Results Posted in the Registry

• Partial Myometrial Resection: 6.9% (2/29) versus 22.6% (7/31) on control; risk difference -15.7 percentage points (95% CI -33.1 to 1.7), risk ratio 0.31 (0.07–1.35); unadjusted two-proportion z-test p = 0.089.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Blood Component Transfusion Requirement

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Partial Myometrial Resection: 58.6% (17/29) versus 61.3% (19/31) on control; risk difference -2.7 percentage points (95% CI -27.5 to 22.1), risk ratio 0.96 (0.63–1.45); unadjusted two-proportion z-test p = 0.833.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Partial Myometrial Resection and the control. The interval gives the range of effects that remain compatible with the data.

Number of Patients Who Met at Least 1 Near Miss Criterion

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Partial Myometrial Resection: 0.0% (0/29) versus 3.2% (1/31) on control; risk difference -3.2 percentage points (95% CI -9.4 to 3.0); unadjusted two-proportion z-test p = 0.329.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Partial Myometrial Resection and the control. The interval gives the range of effects that remain compatible with the data.

Number of Patients Who Had Bladder Injuries

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Partial Myometrial Resection: 3.4% (1/29) versus 6.5% (2/31) on control; risk difference -3.0 percentage points (95% CI -13.9 to 7.9), risk ratio 0.53 (0.05–5.58); unadjusted two-proportion z-test p = 0.594.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Partial Myometrial Resection and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes add descriptive context around the primary screening result, but they address different clinical events and should not be treated as interchangeable measures. The posted results include transfusion requirement, near-miss criteria, and bladder injury. The registry also lists maternal death, intra-surgical bleeding volume, median red blood cell unit transfusion, reoperation, and intensive care admission. Results for those other listed outcomes are not reported in the registry record.

The available secondary counts do not provide a consistent basis for a broad conclusion about comparative outcomes. Some events were uncommon, and estimates based on small counts are inherently imprecise. The transfusion outcome was more frequent in both groups than the rarer event outcomes, but the record’s comparisons still leave uncertainty about the group difference. These outcomes do not validate or overturn the primary result because they measure distinct aspects of care and were not reported as a single combined endpoint.

Secondary findings generally carry less evidential weight when many outcomes are examined without a reported prespecified analysis plan or adjustment for multiple testing. A nominally notable result among several comparisons may occur by chance, while a non-notable result does not establish equivalence. The registry record reports no sponsor analyses and does not specify whether these outcomes were prespecified for inferential testing, how multiplicity was handled, or which outcome was intended to guide conclusions.

Accordingly, the secondary results are best viewed as preliminary descriptive information that may help frame future research questions. They should not be used to make a definitive claim about the procedures’ comparative safety or effectiveness. Their relationship to the primary screening-failure outcome is contextual: they describe other outcomes during follow-up, rather than providing a direct replication of the primary endpoint.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Maternal Death
• Intra-surgical Bleeding Volume
• Blood Component Transfusion Requirement
• Median Transfusion of Red Blood Cell Units (RBCU)
• Number of Patients Who Met at Least 1 Near Miss Criterion
• Number of Patients Who Had Bladder Injuries
• Number of Patients Who Need Surgical Reoperation.
• Number of Patients Who Were Admitted to the Intensive Care Unit.

9. Statistical Interpretation

10. Statistical Methods Explained

The primary comparison is expressed as a risk difference. For a binary outcome, a risk is the proportion of participants in a group who experienced the event. A risk difference subtracts the comparator group’s risk from the other group’s risk. Here, the contrast is partial myometrial resection relative to hysterectomy. A negative estimate therefore indicates a lower observed event proportion in the partial myometrial resection group. This is an absolute comparison, not a relative ratio.

What does the interval represent?

A confidence interval describes the range of effect estimates reasonably compatible with the observed data under the statistical method used. Its width reflects precision: a wider interval indicates less precision. For the primary risk difference, the interval runs from -0.331 to 0.017. Because zero lies within that interval, the data are compatible with no group difference as well as with differences in either direction. The registry record does not identify the confidence level or report a sponsor analysis that produced an interval, so the recalculated interval should be read as an unadjusted estimate based on the posted summary counts.

How should the p-value be read?

The unadjusted primary p-value is 0.089. A p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that null hypothesis and the analysis assumptions held. It is not the probability that the null hypothesis is true, nor does it communicate the effect’s clinical importance or precision. It also does not replace the estimate and interval: the estimate describes the observed contrast, while the interval conveys the uncertainty around it.

Why are these comparisons described as recalculated?

The registry reports counts by group, but the record lists no sponsor-reported statistical analyses. The risk differences, intervals, and unadjusted p-values discussed in this analysis are simple, unadjusted recalculations from the posted summary statistics. They do not represent an adjusted model or a reported sponsor analysis. Such recalculations cannot account for covariates, site differences, or other design features unless those are incorporated in the underlying analysis. The registry record does not report a model or adjustment plan.

Random allocation is intended to support fair comparison by distributing prognostic factors across groups, on average. In an unmasked study, knowledge of the assigned procedure may influence care, outcome assessment, or reporting. The registry identifies the study as randomized and unmasked, but does not report allocation concealment, details of sequence generation, or blinding of endpoint assessment. The record therefore does not allow those potential sources of bias to be evaluated fully.

Why can sparse counts matter?

When binary outcomes occur infrequently, a small change in the number of events can materially change the estimated group contrast. The resulting estimates can be imprecise, as reflected by wide intervals. Standard methods that rely on approximate large-sample behavior may also be less dependable with sparse data. General statistical alternatives can include exact methods or regression methods suited to sparse outcomes, but the registry record does not state that any such methods were used. No new model-based result should be inferred from the posted counts.

Over-dispersion is principally a concern for outcomes modeled as counts or rates when observed variability exceeds what a chosen model expects. General methods may then need to allow for extra variability. The primary endpoint is recorded as a binary participant outcome, not a count rate, and the record does not report an over-dispersion assessment. The registry also lists continuous or event-volume secondary outcomes, but their numeric results and analysis details are not reported in the registry record.

The study’s feasibility framing matters for interpreting all these methods. The record describes randomized procedures and follow-up, but does not report the original statistical plan, analysis population, missing-data strategy, or prespecified handling of multiple outcomes. Consequently, the posted summary comparisons are best treated as descriptive, unadjusted evidence rather than as a complete confirmatory analysis.

11. Confidence Intervals and Precision

Precision is limited for the primary comparison. The risk-difference estimate is -0.157, and its interval extends from -0.331 to 0.017. The range spans zero and includes both a lower event proportion for partial myometrial resection and a possible difference in the opposite direction. The estimate alone should not be treated as a precise measure of the size of any underlying effect.

The group counts are 7 of 31 for hysterectomy and 2 of 29 for partial myometrial resection. With relatively few observed screening failures, individual events have substantial influence on the proportions and their contrast. This is one reason an interval can be wide even when the point estimate appears notable. The interval communicates uncertainty that the point estimate cannot convey.

The unadjusted p-value of 0.089 does not resolve that uncertainty. It does not show that the groups are equivalent, and it does not establish a meaningful difference. A result can have an interval that crosses zero while still being compatible with effects that may matter; deciding what magnitude would matter requires a clinical threshold, which is not reported in the registry record.

The secondary outcomes also have limited precision, particularly where few events are recorded. Their posted comparisons should be read as exploratory. The registry record does not report confidence intervals or sponsor analyses for every listed secondary endpoint, so their uncertainty cannot be fully characterized from the record. Overall, the observed counts offer preliminary information, but the available estimates do not sharply identify the magnitude or direction of comparative differences.

12. 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 effect, not the trial’s original design calculation. For these binary outcomes, the figures mean participants per arm, not total events. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The assumed effect to detect is the stated fraction of the observed effect.

The 80% power column gives an illustrative group size intended to yield an 80% chance of detecting the assumed effect under those planning assumptions, if the assumed effect and model are appropriate. The 90% power column describes the larger group size associated with a 90% chance under the same conditions. These are conditional planning quantities, not observed properties of the completed study.

For the primary endpoint, planning for 100% of the observed effect gives 80 participants per arm for 80% power and 106 participants per arm for 90% power. Planning for 75% of the observed effect gives 157 and 210 participants per arm, respectively; planning for 50% gives 387 and 517. The same general pattern applies across the listed binary outcomes: smaller assumed effects require more participants to detect, because the groups’ outcome proportions are harder to distinguish.

The plotted curve is a visual aid to this relationship between assumed effect size and planning sample size; it does not change the assumptions or turn the observed estimate into a reliable target for a future trial. These calculations are not observed power. The registry record does not report the trial’s own original sample-size assumptions or justification, so the planning illustrations should not be presented as the rationale for the enrollment target.

13. 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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.226; treatment proportion p₁ = 0.069; average p̄ = 0.147.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5013 = 0.9826.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4889 = 0.4115.
4. n = (0.9826 + 0.4115)² / (-0.1568)² = 79.0, rounded up to 80 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
p0 <- 0.225806451612903                          # control proportion
p1 <- 0.0689655172413793                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(5013749)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 80 (80% power), 106 (90% power)
 75% of observed effect: n per arm = 157 (80% power), 210 (90% power)
 50% of observed effect: n per arm = 387 (80% power), 517 (90% power)
power.prop.test: 79 
Simulated power at n = 80 per arm: 0.824 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary endpoint and multiple secondary outcomes. When several outcomes are analyzed, the chance of at least one apparently unusual result can increase if each is tested separately without adjustment. Multiplicity procedures can control the overall false-positive risk or organize outcomes into a prespecified hierarchy. The registry record does not report whether any such procedure was planned or used.

The record also reports no sponsor statistical analyses. It does not provide a statistical analysis plan, prespecified model, analysis population, or protocol deviations. It is therefore not possible to establish from the registry whether the posted comparisons were intended as confirmatory tests, exploratory summaries, or analyses selected after data review. The unadjusted recalculations should not be treated as evidence that multiplicity was addressed.

Missing-data handling is likewise not reported in the registry record. The outcome group sizes are not uniform across the safety and efficacy records, and the record does not explain the relationship between those analysis denominators or whether missing observations, exclusions, or different safety populations account for them. The reasons should not be guessed. No imputation method, missingness assessment, or sensitivity analysis is reported.

The registry does not state whether the primary analysis followed intention-to-treat principles, used a per-protocol population, or included all randomized participants with available outcome data. It also does not describe how participants with an unconfirmed diagnosis were treated in analyses other than the screening-failure endpoint. These omissions limit assessment of possible selection bias and the robustness of the results.

These gaps do not erase the posted counts, but they narrow what can be concluded from them. A complete assessment of inferential strength would require the prespecified analysis plan, participant flow, missing-data accounting, and multiplicity approach. Those details are not reported in the registry 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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: adverse event (18.5%).

The registry reports serious adverse events among the safety groups: 3 affected participants among 33 at risk in the hysterectomy group and 5 among 27 at risk in the partial myometrial resection group. It reports zero deaths in each group. The listed non-serious adverse event counts are zero in both groups, with 33 and 27 participants at risk, respectively. These safety denominators differ from the posted group sizes for the primary outcome, and the registry does not explain the difference.

The serious-event term listed most prominently is “Adverse event” at 18.5%. The record does not provide further detail in the registry entries about the events’ nature, timing, severity criteria, or relationship to the assigned procedure. Serious adverse events are not automatically caused by treatment, and these counts alone cannot establish comparative safety.

Because the study is small and the event counts are limited, the safety figures are descriptive and uncertain. Zero reported deaths does not establish that a risk is absent. The record does not report an adjudication process, a detailed safety analysis plan, or comparative statistical analyses for adverse events.

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

The posted results show a numerical difference in the primary screening-failure outcome between the randomized groups: the reported count was 7 of 31 participants with hysterectomy and 2 of 29 with partial myometrial resection. The unadjusted recalculated risk difference is -0.157, with an interval from -0.331 to 0.017. This interval includes zero, so the data do not pin down a direction or magnitude with precision.

The endpoint is specifically about participants who entered the study but did not show macroscopic findings of placenta accreta spectrum during laparotomy. It is not a direct measure of how well either procedure treats confirmed placenta accreta spectrum. The result should not be generalized to other maternal outcomes, to participants outside the study, or to settings not described in the registry.

The study’s feasibility framing and the absence of a reported sponsor analysis plan further constrain interpretation. The posted summary comparisons are unadjusted recalculations, and the record does not report details needed to evaluate missing data, multiplicity, site variation, or the exact analysis population. The study therefore offers preliminary information rather than a definitive test of comparative effects.

Nothing in these data establishes that either procedure is superior, equivalent, or safer. The secondary outcomes and adverse-event counts provide additional descriptive observations, but they also have limited precision and no reported sponsor statistical analyses. Clinical decisions require broader evidence and individual context; the registry results alone are not a basis for medical advice.

17. Why This Trial Matters Statistically

This trial is statistically important because it places randomization into a feasibility study of two surgical approaches for placenta accreta spectrum. Feasibility work can reveal whether recruitment, random allocation, procedures, and follow-up can be organized in a multicenter setting. It can also show how often the suspected diagnosis was not confirmed at laparotomy, an issue that directly affects how a future trial defines its eligible population and interprets its outcomes.

The primary endpoint also illustrates the difference between an observed contrast and a precise estimate. The groups’ screening-failure counts differ, but the unadjusted interval crosses zero and remains wide. A point estimate can be useful for generating planning hypotheses, yet it is unstable when based on limited outcome information. The sample-size illustrations make clear that detecting smaller effects requires substantially larger groups under the stated assumptions.

The record also highlights why transparent reporting matters. Without the analysis plan, participant flow, missing-data strategy, and multiplicity approach, readers cannot determine how closely the posted results follow a prespecified inferential framework. These omissions are especially relevant when multiple secondary outcomes are listed and only some have posted result counts.

In that sense, the study contributes more as a source of preliminary design and outcome information than as a definitive comparison of procedures. The uncertainty itself is informative: it identifies the limits of what the available data can support and the need for careful planning and reporting in subsequent research.

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 registry record does not report detailed participant characteristics, eligibility criteria, site-specific results, participant flow, or reasons for any exclusions. These details are important for judging how representative the study population was and whether the randomized groups remained comparable in the analyzed outcomes. The enrollment is reported, but the record does not establish how many participants completed each follow-up assessment.

Although the study is identified as randomized and unmasked, the registry does not describe sequence generation, allocation concealment, assessor blinding, or protocol deviations. The intervention descriptions are incomplete in the available record, so the procedures cannot be assessed in full from these registry entries. The study is described as multicenter, but site-level implementation and outcome variation are not reported.

The primary endpoint concerns absence of macroscopic findings at laparotomy, rather than a clinical outcome among confirmed cases. This distinction limits its interpretation as a comparison of the procedures themselves. The record does not report a separate confirmed-case analysis. It also reports a primary endpoint title framed as a percentage while giving group outcome values as counts, without a separate primary percentage result.

Results are not reported for all listed secondary outcomes, and the registry provides no sponsor statistical analyses or detailed safety analysis. The safety denominators differ from the primary outcome group sizes, with no explanation in the registry record. Missing-data methods, analysis populations, multiplicity handling, and the original sample-size justification are also not reported. These limitations make the posted data most suitable for cautious, descriptive interpretation.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Histerectomy Vs Partial Myometrial Resection for Placenta Accreta Spectrum — NCT05013749.
• Registry record last updated 2024-11-25; status last verified 2024-11.
• Results first posted 2024-11-25.
• 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

NCT05013749 is a completed, randomized, parallel-group, unmasked feasibility study sponsored by Fundacion Clinica Valle del Lili. It compared hysterectomy with partial myometrial resection for placenta accreta spectrum, with planned enrollment of 60 and an intended multicenter setting across 3 health institutions.

The primary endpoint was screening failure during surgery: entry into the study without macroscopic findings of placenta accreta spectrum at laparotomy. The reported counts were 7 of 31 in the hysterectomy group and 2 of 29 in the partial myometrial resection group. The unadjusted recalculated risk difference was -0.157, with an interval from -0.331 to 0.017 and an unadjusted p-value of 0.089. The interval includes zero, indicating substantial uncertainty about the group difference.

Some secondary and safety results are posted, but the registry reports no sponsor statistical analyses. Details of the original statistical plan, missing-data handling, and analysis populations are not reported in the registry record. The results are therefore preliminary and descriptive, not a definitive determination of comparative clinical effects.