This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for PROSPER: PostpaRtum PrOphylaxiS for PE Randomized Control Trial Pilot (NCT01274637), a randomized phase 3 study. The primary outcome is Feasibility of Recruitment and Trial Operations..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01274637 |
| Phase | Phase 3 |
| Condition | Venous Thromboembolism, Postpartum |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 62 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Ottawa Hospital Research Institute |
| Results posted | Yes |
2. Clinical Question
Population
The study concerned postpartum women considered at risk of venous thromboembolism. The registry describes the intended population in those terms but does not report more detailed eligibility criteria or participant characteristics in the record. The recorded enrollment was 62.
Intervention
The intervention was prophylactic-dose low-molecular-weight heparin, identified as dalteparin sodium. The arm description specifies subcutaneous injections once daily for 10 (+/- 3 days), for a total of 10 (+/-3) injections. The study was open-label, with no masking.
Comparator
The comparator was a no-treatment control group. The trial used randomized allocation and a parallel-group model. The registry records 30 participants in the low-molecular-weight-heparin group and 32 in the control group.
Primary question
The primary question was about feasibility: how many participants could be recruited per site per month during a 4 months active recruitment phase. The study was described as a pilot intended to assess whether a multicenter randomized trial could be conducted. Its primary endpoint was recruitment and trial operations, not a direct test of whether prophylaxis prevents venous thromboembolism.
3. Trial Design
PROSPER was a randomized, open-label, parallel-group pilot study. The registry lists the phase as phase 3, while the study title and description identify it as a pilot focused on feasibility. These details describe different aspects of the record: the phase classification is listed, and the stated purpose centers on whether a larger multicenter randomized trial could be run.
The two groups were low-molecular-weight heparin and no-treatment control. The treatment arm description names prophylactic-dose dalteparin sodium, administered subcutaneously once daily for 10 (+/- 3 days), with 10 (+/-3) study drug injections in total. Masking was listed as none. The registry records 30 participants in the intervention group and 32 in the control group, for total enrollment of 62.
The listed start was 2011-03, and primary completion was 2014-01. The study status is completed. Ottawa Hospital Research Institute is listed as sponsor. The registry identifies venous thromboembolism and postpartum as conditions associated with the study.
Feasibility was the central design concern. The primary endpoint was the average number of participants recruited per site per month during the 4 months active recruitment phase at each site. The registry record does not report the number of sites, the recruitment period at each site, or a protocol rationale for the planned enrollment. It also does not report a detailed statistical analysis plan, allocation ratio, or sample-size justification. The record includes secondary clinical outcomes, but the study's stated primary purpose remains the assessment of recruitment and trial operations.
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
| Stage | Low Molecular Weight Heparin | Control Group |
|---|---|---|
| STARTED | 30 | 32 |
| COMPLETED | 30 | 30 |
| NOT COMPLETED | 0 | 2 |
Reasons for not completing this period:
| Reason | Low Molecular Weight Heparin | Control Group |
|---|---|---|
| Withdrawal by Subject | 0 | 1 |
| Lost to Follow-up | 0 | 1 |
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.
| Characteristic | Unit | Low Molecular Weight Heparin | Control Group | Total |
|---|---|---|---|---|
| Participants analysed | 30 | 32 | 62 | |
| Age, Continuous | years | 30.0 (20 to 43) | 31.6 (18 to 38) | 30.8 (18 to 43) |
| Sex: Female, Male: Female | Participants | 30 | 32 | 62 |
| Sex: Female, Male: Male | Participants | 0 | 0 | 0 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 2 | 2 | 4 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 28 | 30 | 58 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 1 | 2 | 3 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 4 | 3 | 7 |
| Race (NIH/OMB): White | Participants | 24 | 27 | 51 |
| Race (NIH/OMB): More than one race | Participants | 1 | 0 | 1 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Region of Enrollment: Canada | participants | 27 | 28 | 55 |
| Region of Enrollment: United States | participants | 3 | 4 | 7 |
6. Primary Endpoint
The registry lists the primary outcome as Feasibility of Recruitment and Trial Operations., measured over 4 months.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants per site per month |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint measures recruitment activity: the average number of participants recruited per site per month during a 4 months active recruitment phase at each site. It is a feasibility measure rather than a clinical outcome. A recruitment rate can help researchers judge whether a larger multicenter trial is practically achievable, alongside other operational considerations.
The registry records a value of 0.9 participants per site per month for the low-molecular-weight-heparin group and 0.9 for the control group. These arm-level values do not form a treatment-effect estimate for the clinical question of preventing venous thromboembolism. The record states that values were missing or not estimable for a two-arm comparison for this count endpoint. It therefore does not post an inferential comparison of recruitment rates between groups.
In general, feasibility endpoints are useful because a trial must be recruitable and operable before its clinical questions can be answered reliably at scale. Recruitment rate is only one part of feasibility: by itself, it does not describe retention, adherence, completeness of outcome measurement, or the resources needed to conduct a larger study. Those details are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary result is a recruitment rate of 0.9 participants per site per month in each randomized group. The endpoint was designed to describe recruitment during the active recruitment period, not to estimate the effect of heparin on venous thromboembolism. The registry indicates that a two-arm comparison was not estimable for this count endpoint. There is no posted confidence interval or p-value for a between-group primary comparison.
The matching arm-level recruitment values describe the recorded results, but they do not establish that recruitment would be the same under other study conditions or at other sites. The registry does not report the number of participating sites, site-specific rates, or uncertainty around the average. Without those details, the precision and generalizability of the feasibility estimate cannot be assessed from the posted primary result alone.
The registry also posts a secondary result for major bleeding or clinically relevant non-major bleeding from randomization to Day 90. The reported unadjusted p-value is 0.271. This is a secondary outcome with few observed participants affected, so its estimate is uncertain; the posted result does not provide strong evidence of a difference, but it also cannot rule out clinically meaningful differences. A p-value is not the probability that a hypothesis is true, and a nonsignificant result is not proof of equivalence.
In general, uncertainty is especially important when outcomes are uncommon and the trial is small. Estimates based on sparse event counts can vary substantially with only a small change in the observed data. The registry's posted results do not include a formal analysis for the primary recruitment endpoint or reported analyses for the other listed secondary outcomes. Consequently, this pilot's clinical outcome data should be read as limited descriptive information rather than as a definitive assessment of preventive effectiveness or safety.
9. Statistical Methods Explained
What does the primary endpoint describe?
The primary endpoint is a count-based recruitment rate, expressed as participants per site per month. It captures the pace of enrollment during the active recruitment phase. In general, a rate makes recruitment activity interpretable relative to time and site, but the estimate depends on how the recruitment period and participating sites are defined. The registry specifies a 4 months active recruitment phase at each site, but does not report the number of sites or site-level recruitment results. The posted arm values are 0.9 for each group.
The registry does not post a two-arm comparison for this endpoint, stating that values were missing or not estimable for a comparison. This matters because equal displayed arm values are not themselves a statistical test. A formal comparison would require an estimable contrast and its uncertainty, and neither is posted. No confidence interval or p-value for the primary endpoint is reported in the registry record.
How should the secondary binary result be read?
The posted secondary result concerns participants with major bleeding or clinically relevant non-major bleeding from randomization to Day 90. The record gives counts by randomized group and an unadjusted comparison with p = 0.271. In general, a binary outcome records whether each participant did or did not experience the defined event during the specified period. A risk difference expresses the difference between the groups' event proportions, while a confidence interval describes the range of values compatible with the data under the stated method.
These concepts do not remove the limitations of sparse data. When only a small number of participants experience an outcome, the estimate can be imprecise. The posted comparison is unadjusted, and the record does not report a multiplicity adjustment or a prespecified analysis plan. The confidence limits and other effect estimates are not restated in this interpretation; the key point is that a single unadjusted p-value does not establish either a difference or equivalence.
What do the planning illustrations mean?
The registry includes planning illustrations based on fractions of the observed secondary effect. These are illustrative sample-size calculations, not trial results and not observed power. The record describes the assumptions as a two-sided significance level of 0.05, equal allocation, and a normal approximation. In general, such calculations show how a future study's required participants per arm could change when the assumed effect is smaller or larger. They do not demonstrate that the observed effect is reliable, nor do they validate the design of this pilot.
Because the planning exercise uses an observed effect from a small dataset, the assumed effect may be unstable. Planning for a fraction of that effect can explore sensitivity to a more conservative assumption, but it still does not replace a justified target effect based on the future trial's aims. The registry explicitly distinguishes these calculations from the trial's own design. The sample-size justification for this pilot is not reported in the registry record.
What does over-dispersion mean in general?
For count outcomes, a simple statistical model may assume that variation follows a particular relationship to the average count. Over-dispersion means the observed counts vary more than that model expects. In general, ignoring over-dispersion can make uncertainty estimates too narrow and statistical evidence appear stronger than it should. The registry gives no dispersion estimate for the primary endpoint and does not report a model or adjustment for over-dispersion. It is therefore not possible to determine from the record whether this issue was assessed.
What analysis details are available?
The registry records zero reported analyses for the primary outcome and no reported analyses for the listed secondary outcomes. It does not report the analysis population, handling of missing observations, covariate adjustment, interim analyses, or the statistical plan. In general, these details help readers understand which participants contributed to each estimate and how results were calculated. Without them, the posted numbers can be described, but the analysis cannot be fully reproduced or checked against a prespecified plan.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists five secondary outcomes in addition to the primary feasibility endpoint. It does not report a multiplicity strategy, such as a hierarchy for testing secondary endpoints or an adjustment to account for examining several outcomes. In general, when multiple outcomes are tested, the chance of at least one apparently unusual result can rise if each result is considered separately. Unadjusted secondary p-values should therefore be treated as exploratory unless the analysis plan establishes otherwise.
The record reports no analyses for the primary endpoint and no reported analyses for the listed secondary outcomes. It does not describe whether analyses followed an intention-to-treat, per-protocol, or other analysis population. The number of randomized participants is recorded by group, but the record does not say which participants contributed to each outcome analysis or whether all randomized participants were included.
Missing-data methods are not reported in the registry record. The record does not describe the amount or pattern of missing outcome data, any imputation approach, or sensitivity analyses. In general, missingness can affect an estimate if the likelihood of an outcome being observed is related to participant characteristics or outcomes. Without details about completeness and handling, readers cannot assess the direction or size of possible bias.
The registry also does not report an interim-analysis plan, stopping boundaries, or a detailed statistical analysis plan. These omissions do not show that such methods were or were not used; they mean the relevant information is not reported in the registry record. The posted secondary p-value is explicitly unadjusted, and the record offers no basis for determining whether it was prespecified. These gaps limit reproducibility and make it difficult to distinguish confirmatory analyses from exploratory ones.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Low Molecular Weight Heparin | 2 | 30 | 6.7% |
| Control Group | 0 | 32 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Low Molecular Weight Heparin | 3 of 30 |
| Control Group | 0 of 32 |
Most frequent serious adverse event terms
| Event term | Organ system | Low Molecular Weight Heparin | Control Group |
|---|---|---|---|
| Hospitalization | Pregnancy, puerperium and perinatal conditions | 1 of 30 | 0 of 32 |
| Hospitalization | Infections and infestations | 1 of 30 | 0 of 32 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Low Molecular Weight Heparin | Control Group |
|---|---|---|---|
| Cellulitis | Infections and infestations | 1 of 30 | 0 of 32 |
| Cellulitis | Infections and infestations | 1 of 30 | 0 of 32 |
| Abnormal Lab result | Blood and lymphatic system disorders | 1 of 30 | 0 of 32 |
Serious events with the highest arm-level rate: hospitalization (3.3%).
The registry reports serious adverse events affecting 2 participants in the low-molecular-weight-heparin group and 0 in the control group. It lists hospitalization at 3.3% among the top serious adverse event terms. Other adverse events are recorded for 3 participants in the intervention group and 0 in the control group. The record does not report deaths in either group.
These figures are descriptive counts from a small pilot, not a complete comparative safety analysis. The registry does not provide a statistical comparison for these adverse-event counts or explain how events were collected, classified, or attributed. A difference in recorded counts should not be interpreted on its own as evidence that treatment caused or prevented an event. Conversely, zero recorded events in a group does not establish that the risk is absent.
In general, safety interpretation depends on the definitions used, the period of observation, completeness of reporting, and the number of participants observed. The registry's serious adverse event term and group counts should therefore be read as limited monitoring information. More detailed safety methods and analyses are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
The result principally describes whether recruitment occurred at the recorded pace during a feasibility pilot. The primary measure was 0.9 participants per site per month in each randomized group, and the registry does not post an estimable between-group comparison for that count endpoint. This provides a descriptive recruitment result, not evidence about the clinical effectiveness of postpartum prophylaxis.
The registry's stated purpose was to assess the feasibility of conducting a multicenter randomized trial. The record does not provide enough operational detail to judge feasibility across sites or to determine how other aspects of trial conduct performed. The number of sites, retention, adherence, and completeness of outcome collection are not reported in the registry record.
Clinical outcomes appear as secondary measures, but most do not have detailed results or reported analyses in the record. The available secondary comparison is unadjusted and based on a small number of participants with the outcome. It cannot establish a reliable treatment effect, and a nonsignificant result does not demonstrate that groups are equivalent. The posted safety counts are also descriptive and do not establish causation.
In general, a pilot can inform the design and conduct of later research, but its estimates may be imprecise and should not be mistaken for definitive clinical evidence. The sample-size illustrations are planning exercises based on observed secondary data, not observed power and not proof that a future trial will achieve a particular result. The registry record does not report a sample-size justification for the pilot or a full statistical analysis plan.
Accordingly, the record supports a narrow reading: it reports an arm-level recruitment rate and limited secondary and safety information. It does not resolve whether low-molecular-weight heparin prevents venous thromboembolism in postpartum women at risk. No medical decision should be based on this pilot's posted registry results alone.
13. Why This Trial Matters Statistically
This study is statistically useful because it makes the distinction between feasibility and clinical effectiveness especially clear. Its primary endpoint measures recruitment rate, not a clinical event. A pilot that asks whether a larger randomized trial can be conducted addresses a necessary research question, but its primary result cannot answer whether the intervention changes clinical outcomes.
The primary values are recorded separately by randomized group, yet the registry does not provide an estimable comparison for the count endpoint. That distinction is important: displayed group summaries are not automatically a treatment-effect estimate, and a shared value does not establish equivalence. Without uncertainty estimates or a formal comparison, the strength and precision of the recruitment finding cannot be fully judged.
The record also illustrates why sparse secondary data require restraint. A small trial may collect clinically relevant outcomes, but estimates based on few events are vulnerable to substantial uncertainty. Unadjusted comparisons across several outcomes carry additional interpretive limitations when the analysis plan and multiplicity approach are not reported. The available data can motivate further study, but do not substitute for adequately planned confirmatory evidence.
Finally, the planning illustrations demonstrate a useful distinction between calculations for a future study and power observed in a completed study. They are based on an observed effect and stated assumptions, so they are scenarios rather than guarantees. Reading them as planning tools, rather than as evidence that the pilot was adequately powered for clinical outcomes, preserves the appropriate scope of the study's conclusions.
14. 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 main limitation is the mismatch between the trial's clinical motivation and its primary endpoint. The stated motivation concerns prevention of venous thromboembolism, while the primary measure is recruitment feasibility. That design is appropriate to the stated pilot purpose, but it means the primary result does not estimate a clinical treatment effect.
The registry records enrollment of 62 and group sizes of 30 and 32. With this scale, clinical outcome estimates based on uncommon events are likely to be imprecise. The record does not post an estimable primary two-arm comparison, confidence intervals for the primary endpoint, or detailed analyses for most secondary outcomes. The absence of those results limits assessment; it should not be interpreted as evidence that no events occurred.
Several details needed to evaluate generalizability and conduct are not reported in the registry record, including the number of sites, participant characteristics, detailed eligibility criteria, retention, adherence, and outcome completeness. The record also does not describe the analysis population, missing-data methods, multiplicity handling, interim analyses, or a detailed statistical analysis plan. The sample-size justification for the pilot is not reported in the registry record.
The open-label design means masking was absent, as recorded. The registry does not explain whether this could have affected ascertainment or management of outcomes. The no-treatment control and the specified injection schedule are described, but adherence and co-interventions are not reported. These limitations constrain interpretation of both feasibility and clinical outcome information. They do not establish that the study was conducted improperly; they identify what cannot be assessed from the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: PROSPER: PostpaRtum PrOphylaxiS for PE Randomized Control Trial Pilot — NCT01274637.
- Registry record last updated 2017-08-01; status last verified 2017-01.
- Results first posted 2017-08-01.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
PROSPER, NCT01274637, is a completed randomized, open-label, parallel-group pilot study sponsored by Ottawa Hospital Research Institute. The registry lists phase 3. Enrollment was 62, with 30 participants in the low-molecular-weight-heparin group and 32 in the no-treatment control group. The listed start was 2011-03, and primary completion was 2014-01.
The primary endpoint was average recruitment per site per month during a 4 months active recruitment phase. The posted rate was 0.9 in each group, with no estimable two-arm comparison reported. The registry lists five secondary outcomes; detailed numerical comparison data are posted for major bleeding or clinically relevant non-major bleeding, while analyses for the other listed outcomes are not reported in the registry record.
The study's stated aim was to assess whether a multicenter randomized trial could be conducted. The posted recruitment, secondary outcome, and safety information should be interpreted as limited pilot data rather than a definitive test of clinical effectiveness.