Postpartum Levonorgestrel-releasing Intrauterine System and Breastfeeding: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Postpartum Levonorgestrel-releasing Intrauterine System and Breastfeeding (NCT01555931), a randomized phase 4 study. The primary outcome is Breastfeeding.

2. Clinical Question

The comparison concerns the timing of placement, not whether participants received the system versus no contraceptive intervention. Both groups were assigned placement of a levonorgestrel-releasing intrauterine system, with timing distinguishing the randomized strategies. The primary outcome is a report of any breastfeeding at the final 6 month visit; it is not a measure of breastfeeding duration, exclusivity, or the amount of breastfeeding. Those other measures are not reported in the registry record.

The registry summary describes an intended study of women who planned to breastfeed for at least 6 months, while posted outcome results are reported for the two randomized groups. The actual analysis population and the handling of participants without an outcome report are not reported in the registry record. The clinical question can therefore be stated clearly, but the scope of inference depends on who contributed outcome data and how missing observations were handled, details that are not reported.

3. Trial Design

The registry identifies this as a randomized, parallel-group, open-label clinical trial. Participants were assigned to immediate placement within 48 hours of delivery or placement 4-8 weeks after delivery. The intervention was a levonorgestrel-releasing intrauterine system. Because masking is listed as none, the record does not describe a blinded comparison; whether outcome assessors were blinded is not reported in the registry record.

The study is listed as Phase 4 and completed. The registry gives a start date of 2012-03 and a primary completion date of 2013-06. The sponsor is the University of North Carolina, Chapel Hill. The condition listed is postpartum contraception. The registry enrollment is 61. Separately, the brief summary describes a planned randomized trial of 190 women. The relationship between that planned number and the registry enrollment is not explained in the registry record, so the reason for the difference is not reported.

For the posted primary outcome, the Immediate group has 17 participants and 10 with reported any breastfeeding; the Control group has 18 participants and 9 with reported any breastfeeding. The posted outcome groups therefore provide the basis for the displayed primary comparison, but the registry does not explain the relationship between these group counts and overall enrollment. The analysis population, participant flow, and reasons for any differences in counts are not reported in the registry record.

The registry lists a secondary outcome of LNG-IUS expulsion or removal, measured up to 6 months. It reports two outcome measures in total and one posted secondary outcome. The number of analyses reported is zero. The statistical analysis plan, the originally intended sample-size assumptions, details of allocation concealment, and whether there were interim analyses are not reported in the registry record. These omissions limit what can be inferred about the conduct and prespecification of analyses, even though the assigned comparison and outcome definitions are stated.

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: 26 women failed entry criteria after delivery. Therefore although 61 were enrolled in the original study cohort, only 35 were randomized and allocated to one of the two treatment arms.

Overall Study

Reasons for not completing this 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.

Population: Baseline characteristics of women allocated to immediate or late LNG-IUS placement after delivery.

6. Primary Endpoint

The registry lists the primary outcome as Breastfeeding, measured over 6 months.

The primary endpoint is the number of participants reporting any breastfeeding at the final 6 month visit. It is a binary outcome: each participant either is counted as reporting any breastfeeding or is not counted in that outcome. The registry describes the unit as participants and the timeframe as 6 months. It does not report a more detailed definition of breastfeeding, such as how often it occurred or whether it was exclusive.

This endpoint addresses the trial's stated comparison of breastfeeding frequency between immediate and delayed placement. A binary outcome makes the groups' observed event counts and proportions comparable in a straightforward way. In general, a clearly defined endpoint tied to a specific follow-up time helps readers understand what outcome the comparison represents. Here, the endpoint refers to any breastfeeding reported at the final visit, not breastfeeding throughout the entire period or at every visit.

The registry summary states that the investigators planned to compare breastfeeding prevalence and hypothesized no difference between groups. The endpoint is therefore relevant to the stated research question, but it captures only one aspect of breastfeeding. The registry does not report how the endpoint was collected, how a missing final visit was treated, or whether reports were verified by another source. Those details affect how confidently the count can be interpreted as a complete account of breastfeeding at the stated visit.

7. Results Posted in the Registry

• Immediate: 58.8% (10/17) versus 50.0% (9/18) on control; risk difference 8.8 percentage points (95% CI -24.1 to 41.7), risk ratio 1.18 (0.64–2.16); unadjusted two-proportion z-test p = 0.600.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

LNG-IUS Expulsion or Removal

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Immediate: 47.1% (8/17) versus 0.0% (0/18) on control; risk difference 47.1 percentage points (95% CI 23.3 to 70.8); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Immediate than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry reports one posted secondary endpoint: LNG-IUS expulsion or removal, assessed up to 6 months. This outcome concerns a device-related event, whereas the primary endpoint concerns any breastfeeding at the final 6 month visit. They address different questions and should not be combined into a single overall measure of benefit or harm.

The secondary result may be relevant context for understanding the two timing strategies, but it does not explain or validate the primary breastfeeding comparison. A secondary outcome can differ between groups even when the primary outcome comparison is uncertain, because the endpoints measure different experiences and may have different patterns of occurrence. The registry does not report an analysis connecting expulsion or removal with breastfeeding outcomes, so no relationship between them can be inferred.

Unadjusted secondary results generally carry less confirmatory weight than a prespecified primary analysis. When several outcomes or analyses are examined, the chance of observing an apparently notable result can increase. In general, multiplicity procedures or a prespecified hierarchy can address that issue, but such a strategy is not reported in the registry record. The record lists two outcome measures in total and one posted secondary outcome; it does not report a multiplicity adjustment or the broader set of analyses that may have been planned.

The registry reports no analyses in its analysis listing, so the extent of prespecification cannot be assessed from that listing. The secondary finding should therefore be interpreted as a posted result for a distinct endpoint, rather than as a definitive confirmatory conclusion. It does not change the basic reading of the primary result: the breastfeeding comparison is imprecise, and the secondary outcome does not resolve that uncertainty.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• LNG-IUS Expulsion or Removal

9. Statistical Interpretation

10. Statistical Methods Explained

The primary comparison is presented as a risk difference between the Immediate and Control groups. A risk difference compares the observed event proportions by subtraction and expresses the contrast in absolute terms. The registry reports a positive point estimate, meaning the observed proportion is higher in the Immediate group. The estimate should be interpreted alongside its confidence interval, not in isolation.

What does the confidence interval describe?

In general, a confidence interval describes the uncertainty around an estimated effect under the method used to calculate it. A wider interval indicates less precision than a narrower interval. For this comparison, the reported interval extends across no difference and values in either direction. That breadth means the observed data do not pin down the size or direction of the underlying difference precisely. The interval is not a range containing every plausible individual outcome, nor does it assign a probability to the true effect after the data have been observed.

What does the p-value say?

The registry reports an unadjusted p-value of 0.6 for the primary comparison. In general, a p-value describes how unusual data at least as incompatible with a specified null model would be if that model and the assumptions of the test were correct. It is not the probability that the null hypothesis is true, and it is not the probability that the result happened by chance. The p-value does not measure the size or clinical importance of an effect. Here, the p-value does not indicate strong evidence against no difference, while the confidence interval shows that considerable uncertainty remains.

The term unadjusted indicates that the posted result is not reported as adjusted for other variables or for multiple comparisons. Whether any adjustment was carried out in a separate analysis is not reported in the registry record; the number of analyses reported is zero. The exact test or model used for the primary comparison is not reported. Accordingly, the risk difference, interval, and p-value can be described as posted, but the specific computational assumptions cannot be independently evaluated from the registry record.

Why do the group counts matter?

The primary outcome is binary, and the posted counts are 10 of 17 in the Immediate group and 9 of 18 in the Control group. In general, estimates based on small groups tend to have more sampling variability than estimates based on larger groups, all else being equal. This helps explain why a point estimate can look directionally different while the corresponding interval remains broad. A group-level comparison also does not reveal whether participants differed at baseline or whether outcomes were missing in a way that affected the groups differently; those details are not reported in the registry record.

The displayed comparison includes a risk ratio and an odds ratio as additional ways to express a binary-outcome contrast. In general, a risk ratio compares event proportions as a ratio, while an odds ratio compares the odds of the event. These measures use different scales and should not be treated as interchangeable with an absolute risk difference. Their estimates and intervals are also uncertain in this trial. The registry does not report adjusted versions of these measures or identify a single measure as the prespecified primary analysis.

What does randomization contribute?

Random assignment is intended, in general, to make the groups comparable on average at the time of assignment, including for characteristics that were not measured. It does not ensure that every characteristic is balanced in a small study, and it does not address missing outcome information after assignment. The record identifies the trial as randomized but does not report the sequence-generation method, allocation concealment, baseline characteristics, or analysis population. Those omissions prevent a fuller assessment of how assignment was implemented and how the posted result relates to all randomized participants.

The trial is listed as open-label, with no masking. In general, knowledge of assignment can influence behavior, co-interventions, follow-up, or reporting, depending on the outcome and study procedures. Any such influence in this trial cannot be determined from the registry record. The endpoint is reported breastfeeding at a follow-up visit, but the method of ascertainment and assessor masking are not reported.

Why can over-dispersion matter?

Over-dispersion is a general concern for outcomes modeled as counts when their variability exceeds what a chosen model assumes. It can lead to uncertainty estimates that are too narrow if ignored. The primary outcome is reported as the number of participants with a binary event, not as a rate or repeated count. The registry lists no dispersion measure and does not identify a model that addresses over-dispersion. There is therefore no basis in the record to claim that over-dispersion was relevant to, or accounted for in, the primary analysis.

Finally, the trial's original statistical plan is not reported. The record does not specify its planned primary analysis, covariate adjustment, missing-data method, multiplicity strategy, interim monitoring, or the rationale for the original sample size. These are not details that can be recovered from the posted outcome counts alone. General statistical principles help explain the reported estimate and its uncertainty, but they do not replace the missing trial-specific methods.

11. Confidence Intervals and Precision

The primary risk-difference interval is wide and crosses no difference. Its span includes results in which the observed advantage could favor either group. This is a central feature of the result: the point estimate is not precise enough to settle the direction or size of the underlying difference. The posted interval should be read as a measure of statistical uncertainty under the calculation used, not as a guarantee that the true effect lies within its limits.

The group counts contributing to the primary outcome are 10 of 17 in the Immediate group and 9 of 18 in the Control group. In general, limited information in each group leads to less precise estimates, particularly when the outcome is binary. The posted data illustrate why a visible difference in counts need not translate into a narrow interval or strong evidence of a group difference.

Precision and statistical significance are related but not identical. The p-value of 0.6 does not establish that the groups are equivalent, and the interval's width emphasizes that a range of effects remains compatible with the data. Whether that range is clinically important cannot be determined without a prespecified threshold for meaningful differences, which is not reported in the registry record.

The precision of the posted estimate also depends on how participants and outcomes were handled. The registry does not report missing-data methods, the analysis population, or participant flow. As a result, the interval expresses uncertainty for the comparison as posted, but it cannot account for possible uncertainty introduced by unreported outcome availability or analysis choices.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations computed from the observed effect, rather than the trial's own documented design calculation. The registry record does not report the assumptions used for the original design or the reason for the planned enrollment described in the brief summary.

The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each row asks what sample size would be needed to detect a stated fraction of the observed effect. Planning for 100% of the observed effect gives 499 participants per arm for 80% power and 668 participants per arm for 90% power. Planning for 75% of the observed effect gives 892 participants per arm for 80% power and 1,193 participants per arm for 90% power. Planning for 50% of the observed effect gives 2,012 participants per arm for 80% power and 2,692 participants per arm for 90% power.

In general, a power target is the probability of detecting an effect of a specified size under the assumptions of a particular calculation. The 80% column describes the illustrated sample size for a design targeting an 80% chance of detecting the stated effect; the 90% column uses a higher detection target. These targets are planning quantities, not properties established by the observed trial result. The listed figures are not observed power.

The examples show the general planning relationship: smaller effects require more participants to detect with the same power target, all else being equal. The observed effect is especially uncertain in this study, so using it as the basis for a future planning illustration should not be mistaken for a stable estimate of the effect a future study should expect. The curve should be read as a visual representation of the planning relationship, not as evidence about the trial's original design or its actual probability of finding an effect.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.500; treatment proportion p₁ = 0.588; average p̄ = 0.544.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.7043 = 1.3805.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.7016 = 0.5905.
4. n = (1.3805 + 0.5905)² / (0.0882)² = 499.0, rounded up to 499 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.5                          # control proportion
p1 <- 0.588235294117647                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1555931)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 499 (80% power), 668 (90% power)
 75% of observed effect: n per arm = 892 (80% power), 1,193 (90% power)
 50% of observed effect: n per arm = 2,012 (80% power), 2,692 (90% power)
power.prop.test: 499 
Simulated power at n = 499 per arm: 0.806 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry does not report whether the investigators adjusted for testing multiple outcomes or analyses. The primary endpoint is identified, and one secondary outcome is posted, but the record does not describe a hierarchy of hypotheses, a family of outcomes for formal testing, or a multiplicity correction. The analysis listing contains no reported analyses. It is therefore not possible to determine from the registry record whether the posted p-values were the only comparisons considered or how any broader testing plan was handled.

In general, testing multiple hypotheses can increase the chance of at least one result appearing statistically unusual even when none of the underlying effects is real. This does not mean that a secondary result is necessarily spurious; it means that its evidential weight depends in part on what else was tested and what plan was specified in advance. The absence of a reported adjustment makes the secondary result less suitable for a definitive confirmatory claim.

Missing-data procedures are also not reported. The posted primary-outcome denominators are 17 in the Immediate group and 18 in the Control group, while registry enrollment is 61. The registry does not provide a participant flow account or explain the relationship between enrollment and the outcome group counts. It does not state whether participants without a recorded outcome were excluded, treated as not breastfeeding, imputed, or handled by another method. No such method should be assumed.

The analysis population is not reported in the registry record. It is therefore unclear whether the comparison followed an intention-to-treat approach, a per-protocol approach, or another definition. The record also does not report how withdrawals, protocol deviations, or missing follow-up visits were handled. These omissions matter because the interpretation of a randomized comparison can depend on whether participants are analyzed according to their assignment and how missing outcomes are addressed.

The original statistical analysis plan, interim analysis procedures, and stopping rules are not reported. In general, prespecified methods help distinguish planned analyses from exploratory ones and support interpretation of uncertainty. Without those details, the posted results can be described, but the full risk of selective analysis or missing-outcome bias cannot be assessed.

15. 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 reports serious adverse event counts of zero for the Immediate group and zero for the Control group. It also reports other adverse event counts of zero in both groups. The corresponding at-risk counts are 17 for Immediate and 18 for Control. These figures describe the adverse-event information posted for the groups; they do not establish that no adverse events occurred outside the registry's reporting definitions or observation procedures.

The registry does not list serious adverse event terms. Death counts are not reported in the registry record. The time period and detailed definitions used for adverse-event collection are not specified in the posted safety information, so the counts should not be interpreted beyond what the record states.

Zero reported events in a group is not evidence that the underlying risk is zero. In general, rare events can remain unobserved in a limited group, and safety estimates based on few participants are imprecise. The absence of reported events is a description of the posted counts, not a guarantee about safety or a comparison proving that the groups have identical safety profiles.

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

The posted results describe a randomized comparison of immediate versus delayed postpartum placement and report any breastfeeding at the final 6 month visit. The observed primary counts are directionally higher in the Immediate group, but the unadjusted p-value is 0.6 and the confidence interval is broad. The available data do not establish a clear difference, and they do not establish equivalence.

The result does not show that timing has no effect. Failure to obtain strong statistical evidence of a difference is not the same as evidence that any difference is negligible. Establishing equivalence would require a prespecified acceptable margin and an analysis designed to evaluate that margin; neither is reported in the registry record. The confidence interval remains compatible with effects in either direction, so the estimate is uncertain.

The conclusion applies to the endpoint as defined: any breastfeeding reported at the final 6 month visit. It does not establish effects on breastfeeding exclusivity, duration, continuation between visits, or other outcomes not reported in the registry. Nor does it answer comparisons with no system placement, since both randomized groups were assigned placement, with timing as the contrast.

The size and composition of the analysis population are not fully described. Registry enrollment is 61, while the primary outcome groups reported are 17 and 18 participants. Participant flow and the handling of unreported outcomes are not reported, so the completeness of follow-up and potential effect of missing data cannot be assessed. This limits confidence in extending the posted comparison to all participants described in the trial summary.

The secondary endpoint concerns expulsion or removal, a different outcome that does not settle the breastfeeding question. Safety counts are also limited to the adverse-event information recorded in the registry. Overall, the record supports a careful description of the observed outcomes and their uncertainty, but not a broad claim about clinical effectiveness, equivalence, or safety beyond these reported measures.

17. Why This Trial Matters Statistically

This trial is statistically instructive because its primary comparison has a simple clinical interpretation but substantial uncertainty. The outcome is a binary report of any breastfeeding at a defined follow-up visit, and the registry provides group counts and a risk-difference comparison. Readers can see both the observed direction and the wide uncertainty around it, rather than relying on a single point estimate or p-value.

It also illustrates why a non-significant result should not be translated into a conclusion of no effect. The p-value is 0.6, but the interval spans differences favoring either group. A study can fail to distinguish an effect from no difference while still leaving effects of meaningful size compatible with its data. Equivalence requires a different question and prespecified criteria, which are not reported in the registry record.

The gap between registry enrollment and the posted primary-outcome group counts makes transparent reporting of participant flow and missing-data handling especially important. Without those details, readers cannot determine how the reported comparison relates to all enrolled participants. This is a statistical limitation, not merely a matter of presentation: the analysis population and missing outcomes can influence both the estimate and the interpretation of randomization.

The sample-size illustrations offer another general lesson. Planning calculations that use an observed effect are sensitive to uncertainty in that estimate, and smaller target effects require larger planned groups. Such illustrations can support future study planning, but they are not evidence that the completed trial had adequate power for its intended question. The original design rationale is not reported.

Finally, the single posted secondary endpoint raises the distinction between exploratory and confirmatory evidence. A secondary result can add context, but its weight depends on prespecification and multiplicity methods that are not described. Taken together, the record shows why effect estimates, intervals, outcome definitions, participant flow, and analysis plans all matter alongside a headline significance test.

18. 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.

Several trial-specific limitations affect interpretation. First, the registry does not explain the relationship between enrollment of 61 and the posted primary outcome groups of 17 and 18 participants. It provides no participant flow account, so the reasons for the difference and the status of participants without posted outcome data are not reported. Missing-data handling is also not reported.

Second, the primary endpoint is limited to any breastfeeding reported at the final 6 month visit. The record does not specify the method of ascertainment or provide detail about breastfeeding between visits, duration, or exclusivity. The result therefore addresses a narrow outcome definition rather than every aspect of breastfeeding.

Third, the primary comparison is imprecise. The reported confidence interval includes no difference and values in either direction. The posted p-value does not establish equivalence, and the registry does not report an equivalence margin. The originally intended sample-size rationale and statistical assumptions are not reported, so adequacy for the trial's stated hypothesis cannot be judged.

Fourth, the statistical analysis plan is not reported. The exact primary test or model, any covariate adjustment, multiplicity procedures, interim analyses, and stopping rules are not described. The record lists no reported analyses, which prevents assessment of how closely the posted results follow a prespecified plan.

Finally, the record identifies an open-label randomized design but does not report allocation concealment, assessor masking, baseline characteristics, or the analysis population. These details would help readers assess implementation and potential influences on outcome reporting. The registry summary describes an intended population of women planning to breastfeed for at least 6 months, but characteristics of the participants contributing to posted results are not reported. These limitations do not negate the reported counts; they define the boundaries of what can be concluded from them.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Postpartum Levonorgestrel-releasing Intrauterine System and Breastfeeding — NCT01555931.
• Registry record last updated 2014-08-25; status last verified 2013-06.
• Results first posted 2014-08-25.
• 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.

22. Record Summary

The registry describes a completed, randomized, open-label, parallel-group Phase 4 trial of immediate versus delayed postpartum levonorgestrel-releasing intrauterine system placement. Immediate placement was within 48 hours of delivery; Control placement was 4-8 weeks after delivery. The sponsor is the University of North Carolina, Chapel Hill. The registry lists a start date of 2012-03, primary completion of 2013-06, and enrollment of 61.

The primary outcome was any breastfeeding reported at the final 6 month visit. The posted counts were 10 of 17 participants in the Immediate group and 9 of 18 in the Control group, with an unadjusted p-value of 0.6 and a broad risk-difference interval that includes no difference and effects in either direction. One secondary outcome, LNG-IUS expulsion or removal up to 6 months, is posted. The registry does not report participant flow, missing-data methods, the analysis population, or the original statistical plan.