Breastfeeding and Oral Contraceptives: a Randomized, Controlled Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Breastfeeding and Oral Contraceptives: a Randomized, Controlled Trial (NCT01465022), a randomized na study. The primary outcome is Number of Participants Who Continued to Breastfeed at 6 Months.

2. Clinical Question

The study objectives also identify breastfeeding continuation at 2 months and 4 months, infant growth at 2 weeks and 8 weeks, and continuation of the birth control method at 2 months and 4 months. The stated hypothesis anticipated a difference in breastfeeding continuation at 8 weeks: 35% in the combined-pill group and 60% in the progestin-only group. These percentages are a hypothesis, not reported trial results. The record’s primary outcome is described at 6 months, so it should not be treated as interchangeable with the 8-week hypothesis or with the other specified outcomes.

3. Trial Design

The registry identifies this as a randomized, controlled trial with a parallel-group model. Participants were allocated to a combined estrogen-progestin pill or a progestin-only pill. The record describes masking as quadruple, but does not identify which people or groups were masked, or explain how masking was maintained. Allocation concealment procedures and other details of the randomization process are not reported in the registry record.

The listed enrollment is 197. The record does not explain how enrollment relates to the outcome-specific participant counts, or provide a flow of participants through enrollment, treatment, and follow-up. It lists 64 participants at risk in the combined-pill group and 63 in the progestin-only group in the adverse-event information; these are safety denominators and should not be assumed to be the denominators for the breastfeeding outcome.

The study is marked completed, with a start date of 2005-01 and primary completion date of 2008-06. Its phase is recorded as NA. The sponsor is the University of New Mexico. The registry lists breastfeeding and contraception as conditions and the two contraceptive pills as drug interventions.

The study summary frames the comparison around breastfeeding continuation, infant growth, continued use of the birth control method, and pregnancy rates. The listed primary outcome and secondary outcomes cover only some of those topics; pregnancy rates are named in the objectives, but a pregnancy-rate outcome is not listed among the outcome measures described in the record. The record does not report further design details such as treatment duration, procedures for follow-up, or a protocol for handling treatment discontinuation.

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: The research nurse recruiting the eligible subject will ask the subject if they have been given adequate time to make a decision regarding study participation.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Participants available for follow-up through a 6 month period

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants Who Continued to Breastfeed at 6 Months, measured over Baseline to Week 8, Week 8, 2-6 months.

The primary outcome is titled “Number of Participants Who Continued to Breastfeed at 6 Months.” It is measured as a number of participants, while its description refers to the proportion continuing to breastfeed from 2 months to 6 months after delivery. The registry specifies participants available for follow-up through a 6 month period as the population for this outcome. The listed timeframe includes Baseline to Week 8, Week 8, and 2-6 months, so the record’s wording spans more than a single clearly defined assessment point.

Breastfeeding continuation is relevant to the stated research question because the trial compares contraceptive-pill types in breastfeeding women and explicitly examines whether continuation differs between groups. A count or proportion can describe how many participants meet a defined continuation criterion, but interpretation depends on the exact definition, assessment schedule, and denominator. Those operational details are not reported in the registry record. In particular, the record does not explain whether the 6-month outcome means breastfeeding at a specific visit, any breastfeeding during an interval, or continued breastfeeding throughout a defined period.

No group-specific primary outcome counts, proportions, effect estimate, confidence interval, or test result are reported. The listed measure therefore identifies what the trial intended to assess but does not establish the size or precision of a between-group difference. The primary outcome should also be distinguished from the study summary’s hypothesis about continuation at 8 weeks and from the separate objectives concerning infant growth and contraceptive-method continuation.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Random allocation assigns participants to treatment groups by a chance-based process. In general, randomization is intended to reduce systematic differences between groups at the start of a study, though it does not guarantee that every characteristic will be balanced. The registry identifies random allocation and a parallel-group model, but does not report the sequence-generation method, allocation concealment, or procedures used to assess baseline balance. Those details are not reported in the registry record.

What does a binary outcome mean?

Breastfeeding continuation can be expressed as a binary outcome when each participant is classified according to whether a specified continuation criterion was met. A group count records the number meeting that criterion; a proportion relates that count to a defined denominator. In general, a proportion is interpretable only when the outcome definition, time point, and denominator are clear. The registry names a participant count as the primary measure and describes a proportion, but does not provide the group-specific counts or proportions. It also does not fully define how continuation is assessed across the listed time periods.

How would a group comparison be interpreted?

In general, a treatment-group comparison for a binary outcome can be expressed using an absolute difference in proportions, a relative measure, or another prespecified contrast. Each answers a different question, and an estimate is most informative when paired with a confidence interval. A confidence interval describes the range of values compatible with the observed data under the model and assumptions used; it conveys statistical precision rather than guaranteeing that the true value falls within a particular interval. No primary-outcome estimate or confidence interval is reported in this registry record, so none of these comparisons can be interpreted for this trial from the posted information.

A hypothesis test, when reported, evaluates the data against a specified null model. A p-value is not the probability that the null hypothesis is true, nor does it measure the clinical importance of an effect. Interpretation ordinarily considers the estimated effect and its uncertainty, alongside the study design and outcome definition. Here, the registry does not report a primary-outcome test result or enough outcome data to reconstruct one. It would therefore be inappropriate to characterize the result as statistically significant or not statistically significant.

What does masking contribute?

Masking is intended, in general, to limit the influence of knowledge about treatment assignment on participant behavior, care, or outcome assessment. The registry labels the trial quadruple masked, but does not say which parties were masked or provide operational details. The label alone does not establish how masking worked, whether it remained intact, or how an outcome that may rely on participant reporting was assessed.

How should planning calculations be read?

The record describes sample-size planning illustrations based on a stated fraction of an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. It specifies that the illustrations are planning calculations rather than the trial’s own design justification. In general, a sample-size calculation estimates the number of participants needed under chosen assumptions about the effect, variability, error rate, and allocation. Changing those assumptions changes the planning result. A planning calculation is not “observed power,” which is not a useful substitute for interpreting an estimated effect and its uncertainty.

The registry record does not report a sample-size justification, the original effect assumption used to design the trial, or the details needed to evaluate the planning illustrations against the trial’s actual analysis. It also does not report an observed primary effect in the posted results. Thus the planning description should be kept separate from the treatment comparison: it does not reveal whether the groups differed, or how precisely any difference was estimated.

What analysis details are unavailable?

The record lists zero analyses and does not specify a statistical model for the primary outcome. It does not report whether the primary analysis was adjusted or unadjusted, how missing outcome data were handled, or whether participants were analyzed according to assigned group. It also does not report a prespecified analysis plan or interim-analysis procedures. These omissions limit assessment of analytic choices and of the relationship between the planned outcomes and any reported conclusions. General statistical principles can explain how such choices matter, but cannot establish which methods were used in this trial.

10. Multiplicity, Missing Data and Analysis Populations

The registry describes several outcome questions and assessment periods: breastfeeding continuation, infant growth, and continuation of the birth control method. The study summary also refers to pregnancy rates. When multiple outcomes or time points are tested, there is a general statistical concern that the chance of at least one apparently unusual result can increase if tests are considered independently without a prespecified strategy. Approaches to multiplicity may define a primary comparison, adjust testing, or treat secondary analyses as exploratory. The registry record does not report a multiplicity strategy, and the number of analyses listed is zero.

The primary outcome title refers to breastfeeding at 6 months, while the description refers to continuation from 2 months to 6 months and the timeframe names Baseline to Week 8, Week 8, and 2-6 months. The study objectives separately mention breastfeeding continuation at 2 months and 4 months. The record does not explain how these periods were prioritized or how they relate to the primary outcome definition. This makes it difficult to determine which comparison was intended to carry the main inferential emphasis.

Missing-data handling is not reported in the registry record. The primary outcome population is described as participants available for follow-up through a 6 month period, but the record does not state how many participants had outcome data at each time point, why data might be unavailable, or how missing outcomes were treated. It also does not identify an analysis population, such as all randomized participants or participants with observed follow-up data.

Without these details or outcome results, readers cannot assess whether missingness or multiple comparisons affected the reported evidence. This is a limit on interpretation, not evidence that any particular analysis choice was made.

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 0% reporting threshold.

The registry’s adverse-event information lists 0 serious events among 64 participants at risk in the combined estrogen-progestin group, and 0 among 63 participants at risk in the progestin-only group. It also lists 0 other events among 64 participants at risk in the combined group and 0 among 63 at risk in the progestin-only group. The record does not list deaths or serious-event terms.

These entries describe the counts recorded in the registry for the reported categories and denominators. They are not rates for all possible events, and the record does not specify the adverse-event collection period, definitions, ascertainment procedures, or whether these denominators apply to the full trial enrollment. The reason for the relationship between the safety counts and the listed enrollment is not reported in the registry record.

A zero count in a registry entry means no events were recorded in that entry; it does not establish that an event is impossible or that no unreported events occurred. These safety entries also do not provide evidence about breastfeeding continuation or infant growth. They should be read as limited descriptive reporting rather than as a complete account of safety.

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

The record establishes that a randomized, parallel-group comparison was registered between a combined estrogen-progestin pill and a progestin-only pill for postpartum breastfeeding women. It identifies breastfeeding continuation at 6 months as the primary outcome and describes other interests, including infant growth and continuation of the birth control method. This information helps define the question the trial was designed to address.

The record does not report the primary outcome results, group-specific breastfeeding counts, or a statistical comparison. It therefore cannot establish whether continuation differed between the groups, how large any difference was, or how uncertain an estimate might be. The hypothesis of 35% versus 60% continuation at 8 weeks is an anticipated pattern, not an observed result. It cannot be used to conclude that either group had those rates.

The outcome timing and wording also matter. A hypothesis about 8-week continuation is not the same as the primary outcome titled at 6 months, and the record describes several assessment periods without fully specifying their relationship. The absence of outcome definitions and analysis details further restricts interpretation.

The adverse-event entries report zero serious and zero other events in the listed at-risk groups, but the available information does not show how completely events were collected or what observation period was used. Those entries should not be generalized beyond their recorded categories.

Overall, the registry documents a clinical question and trial design but does not provide the outcome evidence needed to estimate the comparison. The record neither demonstrates a difference nor demonstrates that the groups were equivalent. Determining either would require reported outcome data and an analysis with adequate detail about its population, methods, and uncertainty.

13. Why This Trial Matters Statistically

This trial is statistically notable because its central question concerns a binary outcome assessed over time: whether participants continued breastfeeding. The registry identifies multiple time points and related outcomes, while the stated primary outcome title focuses on 6 months. Clear definitions and a prespecified priority among outcomes are important in general because conclusions can depend on which time point and comparison are treated as primary.

The record also illustrates the distinction between a research hypothesis and an observed result. The stated 8-week values of 35% and 60% describe what was anticipated, but do not report the trial’s findings. Likewise, a completed-trial status does not supply an effect estimate, and a planning illustration does not demonstrate that an effect was observed or precisely estimated.

Randomization and masking are important design features in a treatment comparison, but their labels do not replace reporting of allocation procedures, outcome definitions, follow-up, and analysis. These details help readers judge whether an estimate is interpretable and whether uncertainty is adequately represented. In this record, those methodological details and the primary results are not reported.

The posted safety counts also demonstrate why denominators and collection details matter. Counts without a clear observation period or fuller reporting context cannot describe every possible safety outcome. The central statistical lesson is that trial design, endpoint definition, analysis, and results are distinct parts of the evidence. The registry documents some of these parts, but leaves the core outcome comparison unavailable.

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 principal limitation for interpreting the trial from its registry record is that primary outcome results are not reported. There are no group-specific counts or proportions for breastfeeding continuation, no effect estimate, and no confidence interval or test result. The record lists zero analyses. Without these results, readers cannot assess direction, magnitude, or precision.

The primary endpoint is not fully clear from its title, description, and timeframe. The title refers to participants who continued breastfeeding at 6 months; the description refers to a proportion continuing from 2 months to 6 months; and the timeframe lists Baseline to Week 8, Week 8, and 2-6 months. The record does not clarify how these elements define the outcome or which assessment underlies the primary comparison.

The registry also does not report detailed participant flow, the relationship between enrollment and outcome-specific denominators, or reasons for missing follow-up. The primary outcome population is described as participants available through a 6 month period, but the record does not specify how missing data were handled or which analysis population was used.

Further limitations include the absence of a reported statistical analysis plan, multiplicity strategy, randomization procedures, masking details, and sample-size justification. The planning assumptions do not replace the trial’s original design rationale or its missing results. The safety information is limited to the listed event counts and at-risk denominators; collection methods and observation periods are not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Breastfeeding and Oral Contraceptives: a Randomized, Controlled Trial — NCT01465022.
• Registry record last updated 2016-05-20; status last verified 2016-02.
• Results first posted 2016-01-15.
• 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

NCT01465022 is a completed randomized, controlled, parallel-group trial sponsored by the University of New Mexico. It compared a combined estrogen-progestin pill with a progestin-only pill among postpartum breastfeeding women and is recorded as quadruple masked. The listed enrollment is 197; the study start is 2005-01 and primary completion is 2008-06.

The primary outcome is titled as the number of participants who continued to breastfeed at 6 months. The study summary also describes questions about breastfeeding continuation, infant growth, and contraceptive-method continuation. The record lists zero analyses and does not report primary outcome results or a between-group estimate. Its stated 8-week hypothesis is not an observed result.

The adverse-event entries list zero serious and zero other events in each group, with the reported at-risk counts. Details about outcome analysis, missing data, multiplicity, and event collection are not reported in the registry record.