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 Pericoital Oral Contraception With Levonorgestrel (NCT00922233), a na phase 3 study. The primary outcome is Efficacy: the Pearl Index (Number of Pregnancies Per 100 Woman-years) in the Primary Evaluable Population (18-35).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00922233 |
| Phase | Phase 3 |
| Condition | Healthy |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 72 |
| Arms in the primary outcome | n/a |
| Lead sponsor | FHI 360 |
| Results posted | Yes |
2. Clinical Question
Population
The study enrolled 72 healthy participants. The primary evaluable population was specified as participants aged 18–35. The registry record does not report how many enrollees met that age range or were included in the primary evaluable population.
Intervention
The intervention was levonorgestrel, described as 0.75 mg taken within 24 hours of sex. The study was prospective, open-label, single-arm and multicenter.
Comparator
There was no comparator arm. Allocation is recorded as not applicable, and the study model is single-group. The design therefore does not provide a randomized, concurrent comparison with another method or with no intervention.
Primary question
The primary outcome was the Pearl Index: pregnancies per 100 woman-years in the primary evaluable population aged 18–35. Participants were followed for 6.5 months. The registry record does not report the observed Pearl Index, the number of pregnancies used to calculate it, or a confidence interval.
In practical terms, the study was designed to describe a pregnancy-rate outcome during use of pericoital levonorgestrel, alongside safety and acceptability. The primary outcome description excludes months in which barrier methods, condoms, or emergency contraception were used, unless the participant conceived. That rule defines which observation time contributes to the endpoint; it does not, on its own, establish how many participants or months were included in the final calculation.
Because the study has one group, the central statistical question is descriptive: what pregnancy rate was recorded under the study’s endpoint definition? A comparison with another method is not part of this design. The registry record names acceptability based on reported bleeding patterns as a secondary outcome, but it does not report results for that outcome.
3. Trial Design
This was a prospective, open-label, single-arm, multicenter study of pericoital oral contraception with levonorgestrel. It is recorded as phase 3 and completed. The sponsor was FHI 360. The enrollment count was 72, and the condition was listed as healthy. The study start is recorded as 2010-01 and primary completion as 2010-11.
All participants were assigned to the levonorgestrel arm in the registry record. The intervention description specifies 0.75 mg of levonorgestrel within 24 hours of sex. Allocation is listed as not applicable, masking as none, and the model as single group. These design features mean that the study does not contain a separate randomized control arm. Its findings can describe outcomes among participants in the study, but the design does not directly estimate a difference between levonorgestrel and a concurrent comparison group.
The primary follow-up period is stated as 6.5 months. The primary outcome concerns the Pearl Index in the primary evaluable population aged 18–35. The endpoint description says that months involving barrier methods, condoms, or emergency contraception were excluded unless the participant conceived. The record does not report the size of the primary evaluable population, the number of participants completing follow-up, or the amount of person-time contributing to the endpoint.
The study’s open-label status indicates that masking was not used. The registry record does not report whether any other procedures were used to limit measurement or reporting bias. Nor does it report a protocol-level account of how participants were recruited, how many centers participated, or the schedule of study visits. These details should not be inferred from the multicenter designation alone.
The design is suited to recording outcomes and participant reports during use of the intervention, but it has no concurrent arm for distinguishing the observed outcome from what might have occurred under another approach. Interpretation also depends on the endpoint rules, the evaluated population, and the follow-up actually achieved. Those details are not fully 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
| Stage | Levonorgestrel |
|---|---|
| STARTED | 72 |
| COMPLETED | 68 |
| NOT COMPLETED | 4 |
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 | Levonorgestrel |
|---|---|---|
| Participants analysed | 72 | |
| Age Continuous | years | 32.4 (SD 6.9) |
| Sex: Female, Male: Female | Participants | 72 |
| Sex: Female, Male: Male | Participants | 0 |
| Region of Enrollment: Africa | participants | 72 |
6. Primary Endpoint
The registry lists the primary outcome as Efficacy: the Pearl Index (Number of Pregnancies Per 100 Woman-years) in the Primary Evaluable Population (18-35), measured over 6.5 months.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | pregnancies per 100 woman years |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the Pearl Index, expressed as pregnancies per 100 woman-years in the primary evaluable population aged 18–35. It is a rate that relates pregnancy events to time under observation, rather than simply reporting the proportion of participants who became pregnant. The registry record specifies a follow-up period of 6.5 months and describes which months are excluded from the primary calculation.
In general, a rate can be useful when participants contribute different amounts of observation time. Expressing the result per 100 woman-years gives a common time-based scale for describing pregnancy events. The endpoint is therefore intended to summarize pregnancy occurrence in relation to the eligible observation time, under the stated study rules. The number of pregnancies and the amount of eligible person-time are both important to interpreting such a rate.
The record does not report the Pearl Index estimate, the pregnancy count used for it, the accumulated eligible person-time, or a confidence interval. It also does not report enough detail to independently reconstruct the calculation. The endpoint definition is available, but the observed value and its statistical precision are not reported in the registry record.
The exclusion rule matters to the interpretation: time during use of barrier methods, condoms, or emergency contraception was excluded unless the participant conceived. This definition makes the endpoint specific to the study’s chosen exposure-time rules. It should not be treated as a simple count of pregnancies among all 72 enrolled participants, because the primary evaluable population and eligible follow-up time may differ from total enrollment and total follow-up.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes the study question and endpoint definition, but it does not report the primary outcome result. In particular, no Pearl Index estimate, pregnancy count for the primary calculation, confidence interval, or statistical test result is reported in the registry record. Consequently, the magnitude of the pregnancy rate and the uncertainty around it cannot be described from this record. The endpoint’s stated unit and follow-up duration do not substitute for an observed result.
The enrollment count is 72, but that count should not be read as the number in the primary evaluable population or as the denominator for the Pearl Index. The primary population is identified by age, and the endpoint description applies a rule for excluding certain months of observation. The number of eligible participants and the total eligible person-time are not reported in the registry record. Without those details and the pregnancy count, the rate cannot be independently checked or interpreted for precision.
The single-arm design also limits what can be concluded. Any reported rate would describe the study group under the endpoint’s rules; it would not, by itself, quantify a difference from another contraceptive method or a no-intervention group. There is no randomized comparison in this study. Differences between this group and populations in other studies could reflect differences in participants, follow-up, outcome definitions, or other factors, and the registry record does not provide a basis for adjusting across studies.
The record lists three outcome measures and zero analyses. It identifies acceptability based on bleeding patterns reported as a secondary outcome, but does not report results for that outcome. The primary efficacy result is also absent. Thus, the registry record permits a description of planned outcome concepts and study design, but not a results-based assessment of efficacy or acceptability.
The safety figures are separate from the missing efficacy result. The registry record lists 0 serious adverse events among 72 at risk and 28 other adverse events among 72 at risk. These are counts as recorded, not a substitute for the primary endpoint. Deaths are not reported in the registry record. The record does not provide event terms for serious adverse events.
The sample-size assumptions describe planning illustrations using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects stated as fractions of an observed effect. Those assumptions describe illustrations, not the single-arm design recorded for this study. The primary observed effect is not reported in the registry record, and the illustrations are not evidence of observed power or a study result.
Overall, the registry record supports a cautious description of the design, endpoint definition, enrollment and posted safety counts. It does not support a numerical conclusion about the primary pregnancy rate, its precision, or a comparative effect.
9. Statistical Methods Explained
The primary endpoint is a rate rather than a simple participant-level proportion. In general, a rate relates the number of events to the amount of time participants contribute under the endpoint’s eligibility rules. The Pearl Index expresses pregnancies relative to woman-years and scales that rate to the stated unit of 100 woman-years. For this study, the specified population is aged 18–35, and the endpoint description excludes months involving barrier methods, condoms, or emergency contraception unless the participant conceived.
That distinction between a rate and a proportion is important. A proportion uses a defined group of participants as its denominator and indicates how many experienced an event over a specified period. A rate uses accumulated eligible time as its denominator, so participants with different follow-up durations can contribute different amounts of observation. General statistical interpretation of a rate therefore depends on both the event count and the time at risk. Neither the event count for the primary calculation nor the eligible person-time is reported in the registry record.
A confidence interval would ordinarily express the uncertainty around an estimated rate. In general, it gives a range of values compatible with the data under the chosen statistical method; it does not guarantee that the true value lies in that range. The width depends on information such as the number of events and the amount of observation time, as well as the method used. No confidence interval or other precision estimate for the primary endpoint is reported in the registry record. The endpoint estimate itself is not reported either, so its precision cannot be discussed.
The study is single-arm, with no randomized comparator. In general, a single-group design can describe outcomes observed among enrolled participants, but does not provide a randomized estimate of how those outcomes differ from a comparison group. A comparison against an external rate would require details about the source population and the comparability of outcome definitions, eligibility rules, follow-up, and participant characteristics. Such a comparison is not reported in the registry record and should not be inferred.
Open-label describes a study without masking, as also recorded by the absence of masking. In general, knowledge of the intervention can affect participant reporting or outcome assessment, depending on how outcomes are collected. The primary endpoint is based on pregnancies, but the registry record does not describe the procedures used to ascertain or confirm pregnancies. Acceptability based on bleeding patterns is a reported secondary outcome concept; participant reporting may be relevant to how such an outcome is measured. No specific assessment procedures are reported in the registry record.
The record identifies the study as prospective and multicenter, but does not report the number of centers or the participant-level distribution across them. In general, multicenter data can reflect variation in practice or measurement across sites. Whether such variation was considered in the analysis is not reported in the registry record. No analysis methods or fitted statistical models are reported, and the registry record lists zero analyses.
The sample-size assumptions describe a planning illustration: two-sided significance level 0.05, equal allocation between two arms, normal approximation, and an effect defined as a stated fraction of the observed effect. The assumptions also distinguish total events for time-to-event illustrations from participants per arm for other illustrations. In general, such calculations explore the sample size associated with specified assumptions; they do not describe the number of participants actually analyzed or establish observed power. Here, the recorded study design is single-arm, so the equal-allocation two-arm assumption is not a description of the trial’s allocation. The record does not report the actual planning justification or an observed primary effect, and the illustrations should not be treated as trial results.
Over-dispersion is a general concern when event counts vary more than a simple statistical model expects. If present, it can make uncertainty estimates based on a less variable model too small. The registry record does not report an over-dispersion assessment or a count model for the primary endpoint. It also does not give enough outcome data to assess whether such a concern applies. This is a general methodological consideration, not a finding about this study.
Time at risk also requires clear rules. In general, excluding periods from a rate calculation changes the time represented by its denominator and can affect which events are attributed to the endpoint. The stated rule excludes months involving barrier methods, condoms, or emergency contraception unless conception occurred. The record does not explain in detail how partial months, missing exposure reports, or other deviations from follow-up were handled. Those are relevant implementation details, but they are not reported in the registry record.
Finally, a statistical result needs both a defined analysis population and a result estimate to support interpretation. The registry identifies an age-defined primary evaluable population but does not report its size or detailed inclusion rules beyond the stated month exclusions. It does not report a result, uncertainty interval, or inferential analysis. The design and outcome definition can therefore be explained, but no calculation or conclusion beyond the registry’s posted counts can be reconstructed.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists three outcome measures and identifies acceptability based on reported bleeding patterns as a secondary outcome. The other outcome measures and their definitions are not reported in the registry record. The record lists zero analyses, and it does not report a hierarchy for outcomes, a plan for controlling multiplicity, or an adjustment for multiple statistical tests. Without the analysis details and results, it is not possible to determine whether multiple outcomes or analyses affected the interpretation.
Missing-data handling is also not reported in the registry record. The primary population is described as evaluable and aged 18–35, but the record does not give its size, the number completing follow-up, reasons for missing observations, or methods for handling incomplete outcome or exposure information. It does not report imputation procedures or sensitivity analyses. These omissions matter because the rate depends on both pregnancy events and eligible observation time.
The endpoint description specifies that months involving barrier methods, condoms, or emergency contraception are excluded unless the participant conceived. The record does not report how these periods were identified, how missing reports about those methods were handled, or how the resulting eligible time was assembled. The registry record also does not give a detailed definition of the primary evaluable population beyond the age range and endpoint description.
As a result, the posted information does not establish how missingness, multiple outcomes, or analysis-population choices were handled in practice. These are not evidence of a particular bias or error; they are reporting gaps that limit reproducibility and interpretation.
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 |
|---|---|---|---|
| Levonorgestrel Arm | 0 | 72 | 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 |
|---|---|
| Levonorgestrel Arm | 28 of 72 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Levonorgestrel Arm |
|---|---|---|
| anemia | Blood and lymphatic system disorders | 10 of 72 |
| vaginal candidiasis | Infections and infestations | 5 of 72 |
| headache | Nervous system disorders | 3 of 72 |
| vaginal discharge | Reproductive system and breast disorders | 3 of 72 |
| nausea | Gastrointestinal disorders | 2 of 72 |
| upper respiratory tract infection | Infections and infestations | 2 of 72 |
| vomiting | Gastrointestinal disorders | 1 of 72 |
| irritability | General disorders | 1 of 72 |
| hypersensitivity | Immune system disorders | 1 of 72 |
| Cellulitis | Infections and infestations | 1 of 72 |
The registry record lists 72 participants at risk for serious adverse events and 0 affected. It also lists 72 at risk for other adverse events and 28 affected. These are posted counts for the levonorgestrel arm. The counts should be read as separate safety categories, not combined into a single total. The registry record does not report deaths; a missing death count is not evidence that no deaths occurred.
No specific serious adverse-event terms are listed in the registry record. The posted count of 0 serious adverse events is a descriptive safety figure, not a statistical comparison. With no control arm, the record does not provide a randomized comparison of safety outcomes. It also does not report confidence intervals, event-level detail, or the duration of risk assessment for these safety counts.
The 28 other adverse events are reported as the number affected, but the registry record does not list their terms or severity. The count does not establish how many events occurred, since one participant may have experienced more than one event; event-level counts are not reported. These figures describe what the registry posts and should not be extended to outcomes or details that are absent from the record.
12. What the Result Does, and Does Not, Mean
The study record describes a prospective evaluation of pericoital levonorgestrel, with a primary pregnancy-rate endpoint in participants aged 18–35 and a stated follow-up period of 6.5 months. It records 72 enrolled participants and specifies the dose and timing as 0.75 mg within 24 hours of sex. It also posts safety counts of 0 serious adverse events among 72 at risk and 28 other adverse events among 72 at risk.
The central efficacy result, however, is not reported in the registry record. No Pearl Index estimate, pregnancy count for its calculation, eligible person-time, or confidence interval is posted. This means the observed pregnancy rate and its precision cannot be characterized from the registry information. The endpoint definition alone does not establish the outcome.
Even if a numerical rate were available, the single-arm design would support a description of outcomes in this study group, not a randomized estimate of benefit relative to another method or no intervention. The registry record contains no comparator arm. It also does not report the size of the primary evaluable population or enough details to reconstruct the primary calculation.
The safety counts are likewise descriptive. They do not provide a controlled comparison, and the registry record does not report deaths or specific adverse-event terms. The acceptability outcome based on bleeding patterns is named, but its results are not reported in the registry record.
Accordingly, the record conveys how the trial was structured and which outcomes it set out to assess, but it does not supply the primary efficacy result needed to describe the observed pregnancy rate. These limitations concern what can be concluded from the posted record, not proof that an outcome was absent or that a particular effect did or did not occur.
13. Why This Trial Matters Statistically
This study illustrates why an endpoint definition and an endpoint result are different kinds of information. The registry record precisely names a pregnancy-rate measure, its unit, age range, follow-up duration, and rules for excluding some observation time. Those details help readers understand what the investigators intended to measure. Without the observed rate, event count, and eligible time, however, the outcome cannot be evaluated quantitatively or independently reproduced.
It also illustrates the distinction between a single-group description and a comparative treatment effect. The study is recorded as single-arm, with no allocation to a control group. A rate from one group, even if reported, would not by itself establish how that rate differs from a concurrent alternative. This is a design limitation for comparative inference, rather than a defect in the endpoint’s definition.
The distinction between enrollment and analysis population is another statistical issue. The registry records 72 enrolled participants, while the primary endpoint applies to an evaluable population aged 18–35 and excludes specified months under stated conditions. The record does not state the size of that evaluable population or its eligible observation time. A reader therefore cannot treat the enrollment count as the primary endpoint denominator.
Finally, planning illustrations should not be confused with observed results or observed power. The recorded assumptions describe a two-arm, equal-allocation illustration, whereas this trial is recorded as single-arm. Recognizing that mismatch helps prevent planning calculations from being read as an analysis of the completed study. The record’s incomplete outcome reporting makes that distinction especially important.
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 trial-specific limitation is that the registry record does not report the primary Pearl Index result. It also omits the pregnancy count and eligible woman-time needed to check or interpret the rate, as well as a confidence interval. The primary outcome is therefore defined but not numerically available in the registry record.
The 72 participants enrolled cannot be assumed to equal the primary evaluable population. The endpoint applies to participants aged 18–35 and excludes certain months of observation unless conception occurred. The number meeting the population definition, the amount of follow-up contributing to analysis, and the number completing follow-up are not reported. The record also does not explain how missing exposure or outcome information was handled.
The single-arm design has no concurrent comparator, so it cannot directly estimate a randomized difference between levonorgestrel and another approach. Open-label status is recorded, but outcome ascertainment and assessment procedures are not described in detail. The registry record does not report whether site variation was considered in the analysis, despite identifying the study as multicenter.
Other reporting limitations include the absence of primary analysis methods, confidence intervals, and results for the named bleeding-pattern acceptability outcome. Three outcome measures are listed, but the record does not identify all of them or describe multiplicity handling. Deaths and specific adverse-event terms are not reported. These gaps limit reproducibility and the scope of interpretation; they do not establish what unreported results would have been.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Pericoital Oral Contraception With Levonorgestrel — NCT00922233.
- Registry record last updated 2013-10-29; status last verified 2013-08.
- Results first posted 2013-10-29.
- 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.
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18. Record Summary
NCT00922233 is a completed phase 3, prospective, open-label, single-arm, multicenter study sponsored by FHI 360. It enrolled 72 healthy participants and evaluated levonorgestrel, described as 0.75 mg within 24 hours of sex. The primary endpoint was the Pearl Index in the primary evaluable population aged 18–35, with 6.5 months of follow-up and specified exclusions from eligible observation time.
The registry record does not report the primary endpoint estimate, pregnancy count, eligible person-time, or confidence interval. It lists acceptability based on bleeding patterns as a secondary outcome and reports 0 serious adverse events among 72 at risk and 28 other adverse events among 72 at risk. Deaths are not reported in the registry record. Because the study has no comparator arm, it describes a single group rather than a randomized comparison.