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 Boostrix® Pregnancy Registry (NCT02096276), a registered phase not stated study. The primary outcome is Number of Participants With Known Pregnancy Outcomes, by Type of Pregnancy Outcomes in Women Intentionally or Unintentionally Vaccinated With Boostrix During Pregnancy or Within 28 Days Preceding Conception..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02096276 |
| Phase | Phase not stated |
| Condition | Pertussis |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 1517 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
Population
Pregnant women in the United States exposed to Boostrix during pregnancy or within 28 days preceding conception, with known pregnancy outcomes. The registry accepted voluntary reports. Its primary outcome population included participants with known pregnancy outcomes; the registry record does not report primary outcome counts.
Intervention
The exposure of interest was Boostrix vaccination. The registry record describes intentional or unintentional vaccination, rather than a treatment assigned by the study. The listed study intervention is data collection.
Comparator
No unexposed or otherwise comparable control group is described. The prospective and retrospective exposure groups differ in when the pregnancy was reported relative to outcome documentation, so they should not be read as randomized treatment groups.
Primary question
Among reported pregnancies with known outcomes after the specified exposure timing, what types of pregnancy outcomes occurred, and were those outcomes classified with or without a birth defect? The outcome categories included live birth, spontaneous abortion, stillbirth, and elective termination. The registry was intended to detect and describe abnormal outcomes, including teratogenicity; it does not by itself establish whether exposure caused an outcome.
3. Trial Design
This is a prospective, exploratory pregnancy registry, not a randomized comparison. The registry record lists data collection as the intervention and does not state allocation. It describes two exposure groups: prospective reporting, in which registration occurs before the pregnancy outcome is known, and retrospective reporting, in which the outcome is already known when the pregnancy is registered. Both groups concern Boostrix exposure during pregnancy or within 28 days preceding conception.
Reporting was voluntary and could come from patients and health care providers. The registry aimed to collect information on exposure, potential confounding factors such as other medication exposures, and pregnancy outcomes. Voluntary reporting and differing timing of registration are important features of how the data were assembled; the record does not describe a randomized assignment or a like-for-like control group.
The registry status is COMPLETED. The record gives a start date of 2014-03-31 and a primary completion date of 2019-08-02. Its outcome timeframe states that data were collected between 03 May 2005 to 02 August 2019. These are distinct date descriptions in the record and should not be treated as interchangeable.
Enrollment is listed as 1517, but that number should not be read as the number of participants with known pregnancy outcomes or as the denominator for every reported outcome. The primary analysis population is described as participants with known pregnancy outcomes. The registry record does not report how many enrolled participants had known outcomes, how many were in each outcome category, or an analysis comparing exposed pregnancies with an unexposed group.
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: Total of 1517 pregnancy reports (1455 prospective and 62 retrospective) were collected in the Boostrix US Pregnancy Registry. Of the 1455 prospective reports, 250 had known pregnancy outcomes, 1188 were lost to follow-up and 17 pregnancies were ongoing. Of the 62 retrospective reports, 55 had known pregnancy outcomes and 7 were lost to follow-up.
Overall Study
| Stage | Exposure Group_Prospective | Exposure Group_Retrospective |
|---|---|---|
| STARTED | 250 | 55 |
| COMPLETED | 250 | 55 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: The analysis was performed on total cohort which included participants with known pregnancy outcomes.
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 | Exposure Group_Prospective | Exposure Group_Retrospective | Total |
|---|---|---|---|---|
| Participants analysed | 250 | 55 | 305 | |
| Age, Customized: Pregnant women (13-42 Years) | Participants | 248 | 28 | 276 |
| Age, Customized: Unknown | Participants | 2 | 27 | 29 |
| Sex: Female, Male: Female | Participants | 250 | 55 | 305 |
| Sex: Female, Male: Male | Participants | 0 | 0 | 0 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Known Pregnancy Outcomes, by Type of Pregnancy Outcomes in Women Intentionally or Unintentionally Vaccinated With Boostrix During Pregnancy or Within 28 Days Preceding Conception., measured over Data collected between 03 May 2005 to 02 August 2019: For each subject from date of registration until the pregnancy outcome documentation date (Exposure_Prospective group) or at pregnancy outcome documentation date (Exposure_Retrospective group).
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary outcome is the number of participants with known pregnancy outcomes, classified by type of outcome, among women vaccinated with Boostrix during pregnancy or within 28 days preceding conception. The outcome categories are live birth, spontaneous abortion, stillbirth, and elective termination. The record defines spontaneous abortion as pregnancy loss before 22 weeks of gestation and stillbirth as pregnancy loss at or after 22 weeks of gestation. Each outcome was also classified according to the presence or absence of a birth defect.
This endpoint is used to describe the range and counts of reported pregnancy outcomes after the specified exposure. Categorizing outcomes makes the registry’s descriptive purpose explicit: it can organize outcome information and identify patterns that may warrant further study. A count alone does not measure comparative risk, because no comparable unexposed group is described and the record does not provide the outcome counts needed to calculate rates.
The primary outcome population included participants with known pregnancy outcomes. The registry record does not report the actual primary outcome counts by category, the denominators for those categories, or estimates of uncertainty. It also does not report a primary statistical comparison. Therefore, the endpoint definition is available, but the posted information does not support a quantitative assessment of how often each primary outcome occurred.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry’s stated purpose is to detect and describe abnormal pregnancy outcomes, including teratogenicity, following Boostrix exposure during pregnancy or within 28 days before conception. Its design is descriptive: pregnancy exposure was reported voluntarily, and no randomized or unexposed control group is described. As a result, the record is suited to organizing reported outcomes, not to isolating a causal effect of vaccination.
The primary endpoint is defined in detail, including outcome categories and classification by the presence or absence of a birth defect. However, the record does not report the primary outcome counts. It therefore does not show how many participants had live births, spontaneous abortions, stillbirths, elective terminations, or outcomes with birth defects. Enrollment of 1517 is not a substitute for these outcome-specific denominators, particularly because the primary analysis population is limited to participants with known outcomes.
The available serious adverse event summary gives counts in the prospective and retrospective groups, including affected participants, participants at risk, and deaths. Those figures describe the reported safety fields, but they are not a comparison with an unexposed group. The registry record does not explain the meaning or context of the deaths field in enough detail to interpret it as a pregnancy outcome or as a cause-specific measure. The listed serious terms include spontaneous abortion without birth defects at 1.8%, and several terms at 0.0%; the record does not provide the denominator or calculation details for those percentages.
The registry reports zero analyses. No inferential results, confidence intervals, or hypothesis tests are reported. Consequently, there is no reported estimate of precision for the primary outcome categories and no statistical test supporting a comparison between the two reporting groups. The prospective and retrospective groups also differ in when outcome information was known at registration, so a raw contrast between them would not automatically represent a treatment effect.
Voluntary reporting can affect which pregnancies enter a registry and how completely their outcomes are documented. Potential confounding factors were to be collected, but the record does not report adjustment methods or results. Overall, the record establishes what the registry set out to describe and gives limited safety summary counts; it does not provide the primary outcome results needed to quantify outcome frequencies or draw causal conclusions.
9. Statistical Methods Explained
The record identifies a count-based primary outcome: participants with a known pregnancy outcome, classified by outcome type and by whether a birth defect was present. A count answers how many reported participants fall into a category. To interpret a count as a frequency or rate, its denominator and the way participants entered the analysis must also be clear. Here, the primary population is described as participants with known outcomes, but outcome-category counts and their denominators are not reported.
What descriptive counts can establish
A descriptive registry can document observed outcome categories among reported pregnancies. It can show what was recorded, but a count does not by itself indicate whether an outcome is more common than it would have been without exposure. That comparative question requires an appropriate reference group and comparable ascertainment. Neither an unexposed control group nor a like-for-like comparator is described in the registry record.
General statistical explanation: an estimate is more informative when its uncertainty is also reported. A confidence interval expresses a range of values compatible with the data and the statistical assumptions used. It does not remove bias from voluntary reporting, confounding, or missing outcomes. No confidence intervals are reported for the primary outcomes in this registry record.
Why the group labels matter
The prospective group registered before the outcome was known, whereas the retrospective group registered after the outcome was already known. This timing distinction is part of the registry design. It can affect how information is collected and which pregnancies are reported. The groups should not be treated as randomized arms or as equivalent comparison groups: allocation is not stated, and the record explicitly does not describe a randomized comparison.
General statistical explanation: a comparison between groups is most interpretable when the groups are similar in relevant ways and outcomes are measured consistently. Differences in reporting timing, participant characteristics, or outcome documentation can complicate interpretation. The registry planned to collect potential confounding information, including exposure to other medications, but adjustment procedures and adjusted results are not reported.
Analysis and statistical testing
The registry record reports zero analyses. It does not report hypothesis tests, p-values, model specifications, confidence intervals, or a statistical analysis plan. Without those results, there is no inferential evidence in the record to quantify how precisely the primary outcome counts estimate outcomes in a broader population. Nor is there a reported analysis that compares prospective with retrospective reporting.
General statistical explanation: a p-value, when reported, describes how compatible data are with a specified null hypothesis under the assumptions of a particular test. It does not measure the probability that a treatment caused an outcome, and it does not describe the size or clinical importance of an effect. Since the registry reports no analyses, there is no p-value to interpret for the primary endpoint.
Planning illustrations are not trial results
The record describes planning illustrations based on an observed effect, using a two-sided significance level of 0.05, equal allocation, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. Such illustrations are not evidence that the registry was designed with those assumptions, and they are not observed power. The registry record does not report the study’s own sample-size justification or a statistical plan establishing these assumptions as its design.
General statistical explanation: sample-size planning estimates how much information a future study may need under specified assumptions. It does not reveal the probability that a completed study has found a true effect. In a descriptive registry without a reported control comparison, planning calculations based on an observed effect should be interpreted cautiously and separately from the registry’s outcome counts.
Over-dispersion is relevant to some statistical models for counts when observed variability exceeds what a simpler model assumes. General explanation: ignoring over-dispersion can make uncertainty estimates too narrow. The primary endpoint is described as a participant count, but no count model, dispersion estimate, or model-based analysis is reported, so over-dispersion is not a stated analysis issue in the results.
10. Multiplicity, Missing Data and Analysis Populations
The registry defines one primary outcome measure, with several outcome categories and a further classification according to the presence or absence of a birth defect. The record reports zero analyses and does not report hypothesis tests, secondary statistical comparisons, or a multiplicity adjustment. Whether any formal plan for controlling false-positive findings was specified is not reported in the registry record.
General statistical explanation: multiplicity arises when multiple statistical claims are tested or interpreted. The more tests considered, the greater the chance of at least one apparently unusual result by chance, unless the analysis accounts for that structure. The outcome categories themselves are descriptive classifications; the record does not report tests across them that would require interpreting a multiplicity adjustment.
The primary analysis population is participants with known pregnancy outcomes. This means that the endpoint, as described, does not encompass pregnancies with unknown outcomes. The number of such pregnancies and the reasons outcomes were unknown are not reported in the registry record. Methods for handling missing exposure details, potential confounders, or other variables are also not reported.
Because reports were voluntary and could be prospective or retrospective, outcome availability and reporting timing are relevant to interpretation. General explanation: missing information can bias a result when inclusion or documentation is related to exposure, outcome, or participant characteristics. The registry record does not provide enough information to assess whether or how this occurred, or whether any sensitivity analysis was performed. No imputation or other missing-data method is reported.
The record does not describe additional analysis populations, exclusions, or rules for handling incomplete records beyond specifying known outcomes for the primary population. The magnitude and direction of any resulting selection effects cannot be determined from the posted information.
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 |
|---|---|---|---|
| Exposure Group_Prospective | 3 | 250 | 1.2% |
| Exposure Group_Retrospective | 1 | 55 | 1.8% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Exposure Group_Prospective | 3 of 250 |
| Exposure Group_Retrospective | 6 of 55 |
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 |
|---|---|
| Exposure Group_Prospective | 0 of 250 |
| Exposure Group_Retrospective | 0 of 55 |
Most frequent serious adverse event terms
| Event term | Organ system | Exposure Group_Prospective | Exposure Group_Retrospective |
|---|---|---|---|
| Spontaneous abortion without birth defects | Pregnancy, puerperium and perinatal conditions | 3 of 250 | 1 of 55 |
| Spontaneous abortion with birth defects | Pregnancy, puerperium and perinatal conditions | 0 of 250 | 0 of 55 |
| Elective termination without birth defects | Pregnancy, puerperium and perinatal conditions | 0 of 250 | 0 of 55 |
| Elective termination with birth defects | Pregnancy, puerperium and perinatal conditions | 0 of 250 | 0 of 55 |
Serious events with the highest arm-level rate: spontaneous abortion without birth defects (1.8%), spontaneous abortion with birth defects (0.0%), elective termination without birth defects (0.0%), elective termination with birth defects (0.0%).
The serious adverse event summary lists separate figures for the prospective and retrospective exposure groups. For the prospective group, the serious-event fields show 250 at risk and 3 affected; the other-event fields show 250 at risk and 0 affected, with 3 deaths listed. For the retrospective group, the corresponding serious-event fields show 55 at risk and 1 affected; the other-event fields show 55 at risk and 0 affected, with 6 deaths listed. These are the counts as recorded, not a comparison with an unexposed group.
The serious terms summary lists spontaneous abortion without birth defects at 1.8%, and spontaneous abortion with birth defects, elective termination without birth defects, and elective termination with birth defects at 0.0%. The registry record does not report the denominator or calculation details for these percentages, so they should not be treated as rates with a known population basis.
The deaths field is reported as a count, but its meaning and relationship to pregnancy outcomes are not explained in the registry record. It should not be assumed to describe maternal deaths, fetal deaths, or a specific cause of death. The groups also differ in reporting timing, and no comparative analysis is reported. These safety figures are descriptive registry entries; they do not establish causation or a difference in risk.
12. What the Result Does, and Does Not, Mean
The registry is designed to describe pregnancy outcomes after Boostrix exposure during pregnancy or within 28 days before conception. It specifies outcome categories and records whether a birth defect was present. This makes the intended descriptive question clear and provides a framework for organizing reports from exposed pregnancies.
The posted record does not report the primary outcome counts or denominators by category. It therefore cannot show the frequency of live births, spontaneous abortions, stillbirths, elective terminations, or birth defects among the primary analysis population. Enrollment of 1517 does not fill that gap: the primary population is defined by known outcomes, and the record does not state how many participants were included in that population.
The available serious adverse event counts and term percentages are descriptive. They do not establish that vaccination caused an event, nor do they establish that it did not cause an event. There is no unexposed control group described, no randomized allocation, and no reported statistical comparison. The prospective and retrospective groups are distinguished by the timing of registration relative to the known outcome, not by assigned treatments.
General statistical explanation: an absence of reported evidence is not the same as evidence that an event cannot occur. Conversely, an event recorded after exposure is not, on timing alone, proof that exposure caused it. Assessing causality requires appropriate comparison, measurement, and consideration of confounding and selection; the registry record does not report such an analysis.
The interpretation is therefore limited to the registry’s aims, outcome definitions, and the descriptive safety fields that are reported. The primary outcome results and their precision are not reported in the registry record. No treatment recommendation or conclusion about individual risk follows from these registry entries alone.
13. Why This Trial Matters Statistically
Pregnancy registries address an important statistical challenge: outcomes may need to be documented after an exposure that occurs outside a randomized study. A registry can collect exposure timing and pregnancy outcomes prospectively, and can organize reports across clinically meaningful outcome categories. In this case, the registry also distinguishes prospective reporting from retrospective reporting, making clear that the timing of outcome knowledge varies across records.
That structure matters statistically because outcome ascertainment and participation can depend on how and when a pregnancy is reported. Voluntary reporting can produce a selected set of records rather than a representative sample, and the retrospective group has outcome information known at registration. These features do not invalidate descriptive data, but they shape what those data can support and how any comparison should be interpreted.
The record also illustrates why an enrollment figure and an endpoint result are not interchangeable. The stated primary population is limited to participants with known pregnancy outcomes, while the primary outcome counts are not reported. Without those counts and relevant denominators, readers cannot quantify outcome frequencies or assess their precision.
The registry’s value is therefore distinct from that of a controlled efficacy or safety comparison. Its stated purpose is to detect and describe outcomes after exposure, including abnormal outcomes and teratogenicity. The record provides outcome definitions and limited serious adverse event summaries, but no primary outcome analysis. Recognizing this distinction prevents descriptive monitoring from being mistaken for causal evidence.
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 primary limitation in the posted record is that the defined primary endpoint is not accompanied by its outcome counts or denominators. The primary population includes participants with known outcomes, but the number of participants with known outcomes is not reported. Enrollment is not an adequate substitute for the analysis denominator.
Voluntary reporting may affect which pregnancies are registered. The record does not report the number or characteristics of unreported eligible pregnancies, so the extent to which the registry reflects all exposed pregnancies cannot be assessed. The prospective and retrospective groups also differ in whether the pregnancy outcome was known at registration. This can affect documentation and selection, but the registry record does not quantify those effects.
No unexposed control group or randomized allocation is described. Potential confounding factors, including exposure to other medications, were to be collected, but the record does not report adjustment methods or results. It is therefore not possible to separate the association of exposure with an outcome from other factors using the posted information.
The safety summary includes counts and selected term percentages, but the basis for the percentages is not reported. The context and definition of the deaths field are also not reported in enough detail to interpret those counts as a particular type of death or outcome. The registry record does not report confidence intervals, hypothesis tests, a statistical analysis plan, or methods for handling missing information beyond limiting the primary population to participants with known outcomes.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Boostrix® Pregnancy Registry — NCT02096276.
- Registry record last updated 2020-12-19; status last verified 2020-11.
- Results first posted 2020-12-19.
- 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
NCT02096276 is the Boostrix® Pregnancy Registry, sponsored by GlaxoSmithKline and listed as COMPLETED. The registry aimed to detect and describe pregnancy outcomes, including abnormal outcomes and teratogenicity, after intentional or unintentional Boostrix exposure during pregnancy or within 28 days preceding conception.
The design includes voluntary prospective and retrospective reporting in pregnant women in the United States. Enrollment is listed as 1517. The registry start date is 2014-03-31, the primary completion date is 2019-08-02, and the stated outcome data collection period is 03 May 2005 to 02 August 2019.
The primary measure is the number of participants with known pregnancy outcomes, classified by outcome type and presence or absence of a birth defect. The record defines the outcome categories but does not report their primary counts or a statistical analysis. A serious adverse event summary is reported, without a described unexposed comparison or inferential results.