Timing of Antibiotic Prophylaxis for Cesarean Deliveries: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Timing of Antibiotic Prophylaxis for Cesarean Deliveries (NCT00805545), a randomized na study. The primary outcome is Endometritis and Wound Infection.

2. Clinical Question

The underlying clinical contrast is timing, not antibiotic versus no antibiotic: both groups were assigned an antibiotic strategy. The registry’s background describes antibiotic prophylaxis as standard practice for cesarean delivery and says the general practice is administration after the cord is clamped. The study asks whether moving prophylaxis earlier, before incision, changes postpartum infectious morbidity.

The outcome is reported as the number of patients infected, with endometritis and wound infection named together in the primary outcome title. The registry does not give separate counts for the two conditions or a detailed case definition, so the exact rule for classifying an infection cannot be determined from the record. The primary results provide counts for each timing group, but do not provide a sponsor-reported test or direct estimate of the difference between groups.

3. Trial Design

The registry identifies this as a randomized, parallel-group trial with no masking. It lists an enrollment of 400 and a completed status. The listed start is 2008-11, and primary completion is 2009-11. Phase is recorded as NA. The sponsor is the University of Florida. These registry descriptors establish the general structure and timing of the study, but do not provide the full protocol or operational details.

Participants were assigned to one of two antibiotic-timing strategies. The preoperative group was to receive antibiotics 30-60 minutes before incision. The post-cord-clamping group was to receive antibiotics immediately after the umbilical cord was clamped. The record describes both interventions simply as antibiotic drugs and does not identify their names or dosing details. Since masking is listed as none, the trial is recorded as unmasked; the record does not describe whether outcome assessors were separately blinded.

The outcome population is described as participants who received their assigned timing strategy and completed the study: 194 in the preoperative group and 197 in the post-cord-clamping group. The record does not give a participant flow account explaining the relationship between the enrollment figure and these analyzed groups. It also does not report reasons for non-completion, protocol deviations, or a specific intention-to-treat analysis.

Follow-up for the primary outcome ran from the time of surgery until 6 weeks postpartum. The registry lists one outcome measure and does not post secondary outcomes. Although the trial is marked completed, the posted record does not contain a reported statistical analysis for the arm comparison. Details such as the randomization method, allocation concealment, sample-size justification, interim monitoring, and prespecified statistical plan are not reported in the registry record. These omissions limit how fully the design and analysis can be assessed.

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: We used computer generated random numbers to assign patients to the two groups. Patients were excluded from the study if they were allergic to either of the study drugs or if they had evidence of infection prior to surgery.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All 194 patients who received preoperative antibiotics and who completed the study were analyzed. All 197 patients who received post-cord clamping antibiotics and who completed the study were analyzed.

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 Endometritis and Wound Infection, measured over Patients were followed from the time of surgery until 6 weeks postpartum..

The primary outcome is titled “Endometritis and Wound Infection” and measures the number of patients infected. Follow-up is described as extending from surgery until 6 weeks postpartum. The outcome description identifies maternal infections after cesarean delivery as the concern being studied and asks whether the timing of antibiotic prophylaxis changes infectious morbidity.

Counting infected patients is a clinically interpretable way to summarize how many participants in each group met the outcome definition during the follow-up period. The title appears to group endometritis and wound infection within one endpoint, but the registry does not state whether a participant could be counted for either condition, how diagnoses were confirmed, or whether the reported count is a combined measure under a specific rule. Separate counts for endometritis and wound infection are not reported in the registry record.

The registry gives 6 infected patients in the preoperative group and 4 in the post-cord-clamping group, with analyzed group sizes of 194 and 197, respectively. It also reports a 95% confidence interval for each arm’s endpoint value: 0.142 to 7.28 for preoperative antibiotics and 0.372 to 11.34 for post-cord-clamping antibiotics. The record does not explain the scale or calculation underlying these intervals. They are arm-specific intervals, not a confidence interval for the difference between strategies.

The endpoint captures maternal infection but, by itself, does not quantify fetal or newborn outcomes. Although concern about fetal exposure appears in the outcome description, a corresponding baby-focused result is not posted with the primary outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized, parallel-group comparison of two antibiotic timing strategies. Randomization is intended, in general, to support a fair comparison by allocating participants to strategies without basing assignment on their prognosis. In an unmasked trial, participants and study staff may know the assigned timing; whether outcome assessors were blinded is not reported in the registry record. Randomization does not by itself guarantee that every later analysis is unbiased: the analysis population, missing outcomes, outcome definition, and treatment of deviations also matter.

What does the endpoint count represent?

The primary measure is the number of patients infected, for an outcome titled endometritis and wound infection. A count is a direct summary of recorded events, but interpretation also depends on the number of people evaluated and on how the endpoint was defined. The record gives 194 analyzed participants for preoperative antibiotics and 197 for post-cord-clamping antibiotics. It does not describe the infection case definition, ascertainment procedures, or whether the count combines participants with either condition under a prespecified rule. It also does not give separate component results.

For outcomes that can occur in a participant, analysts often report a count alongside the group size or a proportion, then estimate a contrast between the groups. The registry gives the counts and analyzed group sizes but does not post a comparative effect estimate. No new effect estimate should be inferred from the arm summaries without specifying the analysis and assumptions. In particular, the listed confidence intervals belong to individual arms; they are not the uncertainty interval for a contrast.

How should confidence intervals be understood?

In general, a confidence interval describes statistical uncertainty in an estimate under the method used to construct it. A wider interval indicates less precision, while a narrow interval indicates greater precision, conditional on that method and its assumptions. A confidence interval does not give the probability that a specific fixed effect lies within the interval. It also does not, on its own, establish clinical importance or prove that there is no effect.

The registry reports a 95% confidence interval of 0.142 to 7.28 for the preoperative group and 0.372 to 11.34 for the post-cord-clamping group. The record does not identify the scale, method, or specific quantity to which these intervals refer beyond listing them with the arm results. They should be quoted as recorded rather than reinterpreted as intervals for rates, risk differences, or another unreported measure. No confidence interval for the between-group comparison is posted.

Why does the analysis population matter?

The primary outcome description says that 194 participants who received preoperative antibiotics and completed the study were analyzed, and that 197 who received post-cord-clamping antibiotics and completed the study were analyzed. This wording identifies a completed-participant analysis group. An intention-to-treat analysis generally aims to analyze randomized participants according to their assigned group, whether or not they fully adhered to the assigned strategy. A completed-participant analysis may differ if some randomized participants did not complete follow-up or were excluded. The record does not report the randomized group totals, reasons for non-completion, or whether another analysis population was used.

For missing outcome data, analysts may use different approaches depending on why data are missing and what assumptions are defensible. The registry does not state whether missing outcomes occurred, whether any imputation was used, or whether sensitivity analyses were performed. Thus, the extent to which missingness could affect the reported counts cannot be assessed from the posted record.

What is not available about the statistical plan?

The record lists one outcome measure and no secondary outcomes, and it posts no statistical analyses for the comparison. Details of the planned model, hypothesis test, significance threshold, handling of protocol deviations, and any covariate adjustment are not reported in the registry record. The sample-size justification and planned interim analyses are also not reported. Without those details, it is not possible to determine whether the posted endpoint was analyzed as originally planned or to assess the intended precision of the trial.

In general, over-dispersion matters when count data vary more than the statistical model expects. A model that assumes less variability than is present can produce uncertainty estimates that are too small. Whether over-dispersion is relevant depends on the specific outcome model and data structure. The registry does not report a count model or any assessment of over-dispersion, so no trial-specific claim can be made about it.

These methods points distinguish the descriptive information that is posted from a complete comparative analysis. The registry supplies event counts, group sizes, and arm-specific intervals, but not the model or inferential result needed to quantify the uncertainty around the contrast between antibiotic timing strategies.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, the primary outcome of endometritis and wound infection, and no posted secondary outcomes. It also records no posted statistical analyses. With one listed endpoint, the record does not present a family of multiple posted outcomes for which a multiplicity adjustment can be evaluated. However, absence of listed secondary outcomes does not establish that the study protocol had no additional planned outcomes or analyses; such protocol details are not reported in the registry record.

Multiplicity arises in general when several statistical hypotheses are tested, because interpreting many tests can increase the chance of a misleading positive finding unless the analysis plan addresses that issue. The posted record does not identify a testing hierarchy, adjustment method, or planned set of comparisons. Since no sponsor-reported comparison test is posted, there is no reported p-value to interpret or adjust.

The primary analysis population is described as participants who received the relevant antibiotic strategy and completed the study: 194 in the preoperative group and 197 in the post-cord-clamping group. The record does not report the number randomized to each arm, the reasons that other enrolled participants are not included in these endpoint populations, or whether an intention-to-treat analysis was conducted. It does not state how missing outcomes were handled, whether participants were excluded for protocol deviations, or whether any imputation or sensitivity analysis was performed.

These gaps matter because the interpretation of a randomized comparison depends not only on the random assignment but also on how participants are retained in the analysis and how missing outcomes are treated. The posted counts can be described for the completed-participant groups, but the registry record does not permit an assessment of the potential influence of missing data or a comparison across alternative analysis populations.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 2% reporting threshold.

Most frequent non-serious adverse event terms

The registry’s safety figures report 0 serious adverse events among 200 participants at risk in the preoperative antibiotic group and 0 among 200 at risk in the post-cord-clamping group. It also reports 6 other adverse events among 200 at risk in the preoperative group and 4 among 200 at risk in the post-cord-clamping group. These safety figures are separate from the primary infection outcome counts, which are reported for analyzed groups of 194 and 197 participants. The different denominators should not be treated as interchangeable.

Zero recorded serious events means none were entered in this safety summary; it does not establish that a strategy has no serious risks. Rare outcomes can be difficult to characterize from a limited number of observed events, and the registry does not provide a comparative safety analysis. The serious adverse event terms list is empty. Deaths are not reported in the registry record.

The other adverse event counts are also descriptive. The registry does not provide event definitions, severity details for these events, or an analysis comparing the groups. These counts alone do not establish that the groups had different overall safety profiles. They should be read as the safety figures recorded, with the population and reporting details as stated, rather than as a comprehensive assessment of all possible harms.

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

The posted results document that the registry recorded 6 patients with endometritis and wound infection in the preoperative antibiotic group and 4 in the post-cord-clamping group. The outcome was followed from surgery until 6 weeks postpartum. The analyzed populations were 194 and 197 participants, respectively. These findings describe the completed-participant groups reported in the record.

They do not, on their own, establish that one timing strategy is better, worse, or equivalent to the other. The registry does not provide a between-group effect estimate, confidence interval for the contrast, or p-value. The arm-specific intervals do not answer the comparative question. A formal analysis would be needed to estimate the contrast and its precision, and the methods used for such an analysis are not reported.

The result also does not establish the absence of an effect. With a small number of recorded infections, the observed counts may be compatible with a range of underlying outcomes; the registry’s posted information does not quantify the uncertainty of the difference. At the same time, no claim about a particular clinically important difference can be made from the counts alone.

The endpoint is maternal infection. The outcome description raises a question about fetal exposure and risk to the baby, but no baby-focused outcome result is posted with the primary measure. Consequently, the maternal infection results do not answer that separate safety question. The registry also does not report the drug, dose, or route, nor does it supply details that would allow the antibiotic strategies to be characterized beyond their timing.

The most defensible reading is therefore descriptive and limited: the recorded infection counts were 6 and 4 in the two analyzed groups, with the stated follow-up and arm-specific confidence intervals. The record does not report a statistical comparison or enough analytic detail to establish a causal or clinical conclusion from these results.

13. Why This Trial Matters Statistically

This trial is statistically useful as an example of why observed event counts are not the same as an estimated treatment contrast. The registry gives the number of patients with the outcome in each group, together with analyzed group sizes, but does not provide a direct comparative estimate. Readers may be tempted to focus on the fact that the counts are 6 and 4. Without a reported analysis of the difference and its uncertainty, those counts alone cannot answer the randomized comparison.

It also illustrates the importance of distinguishing outcome uncertainty from comparative uncertainty. The registry lists a 95% confidence interval for each arm, but not for the difference between the strategies. In general, arm-specific uncertainty intervals and a confidence interval for a treatment contrast answer different questions. The registry does not explain the interval scale or method, so their interpretation should remain limited to what is explicitly recorded.

Another statistical consideration is the analysis population. The primary results describe participants who received the assigned timing and completed the study, rather than explicitly describing an analysis of all randomized participants. Without participant flow and missing-data details, readers cannot fully judge how this analysis relates to the original randomized groups. This is a reminder that transparent reporting of enrollment, follow-up, exclusions, and analysis populations is essential for interpreting trial results.

Finally, the clinical question includes both maternal infection and concern about fetal exposure, while the posted primary outcome is maternal infection. A clear distinction between the question being raised and the outcomes actually reported helps prevent conclusions from extending beyond the available evidence. The statistical record is most informative when the endpoint, population, uncertainty, and limits of the analysis are read together.

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 record leaves important aspects of the trial’s methods and results unspecified. It does not report the antibiotic name, dose, or route, and it does not provide detailed eligibility criteria or the full protocol. The allocation method beyond randomized assignment, allocation concealment, and any blinding of outcome assessors are not reported. Although the trial is listed as unmasked, the record does not describe how outcome assessment was conducted.

The primary endpoint combines endometritis and wound infection in its title, but the record does not provide the diagnostic definitions, adjudication process, or component-specific counts. The meaning and construction method for the listed arm-specific confidence intervals are also not explained. Most importantly for the comparative question, there is no posted effect estimate, comparison confidence interval, p-value, or analysis method.

The outcome population is described as participants who received the assigned strategy and completed the study. The record does not provide a participant flow accounting for the enrollment of 400, the numbers randomized to each arm, or the reasons for differences between enrollment and the endpoint analysis groups. Missing data, protocol deviations, imputation, and sensitivity analyses are not reported. These omissions make it difficult to assess the potential impact of excluding participants or of incomplete follow-up.

The registry lists no secondary outcomes and posts no statistical analyses. A sample-size justification, interim analysis plan, and prespecified analysis plan are not reported in the registry record. The primary endpoint follows participants through 6 weeks postpartum, so outcomes beyond that period are not addressed by the stated follow-up. The registry also does not post baby-focused outcomes, despite the concern about fetal exposure in the outcome description. Together, these limits restrict interpretation to the descriptive maternal infection counts and recorded safety figures.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Timing of Antibiotic Prophylaxis for Cesarean Deliveries — NCT00805545.
• Registry record last updated 2012-04-16; status last verified 2012-03.
• Results first posted 2012-04-16.
• 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.

18. Record Summary

NCT00805545 is a completed randomized, unmasked, parallel-group trial sponsored by the University of Florida. It lists an enrollment of 400 and compares antibiotics administered 30-60 minutes before incision with antibiotics administered immediately after umbilical cord clamping. The listed start is 2008-11 and primary completion is 2009-11.

The primary outcome is endometritis and wound infection, measured as patients infected and followed from surgery until 6 weeks postpartum. The registry reports 6 infected patients among 194 analyzed in the preoperative group and 4 among 197 analyzed in the post-cord-clamping group. It lists arm-specific 95% confidence intervals but does not report a statistical comparison between groups. No secondary outcomes or statistical analyses are posted. The record does not report detailed endpoint definitions, missing-data methods, or the study’s statistical plan.