Immediate Postplacental IUD Insertion: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Immediate Postplacental IUD Insertion (NCT02169869), a randomized na study. The primary outcome is Proportion of Subjects With an IUD at 3 Months Postpartum.

2. Clinical Question

The registry describes a randomized comparison after delivery among participants who consented and met the study criteria. This makes the timing of IUD placement the central contrast. The primary outcome description specifies that participants were contacted at 3 months after delivery and asked whether they had an IUD in place. The registry lists 17 participants in the immediate group and 16 in the 6-week group, with 12 and 5 participants, respectively, counted as having the outcome. The resulting comparison concerns the recorded group results in this small trial; the record does not establish how applicable they are to populations with different eligibility criteria or care settings.

3. Trial Design

The registry describes a randomized, parallel-group clinical trial with no masking. Participants were randomized after vaginal or cesarean delivery to immediate postplacental IUD insertion or insertion at the routine postpartum visit. The planned immediate placement window was within 60 minutes of placental delivery, and the comparator is described as 6 weeks postpartum. Because masking was listed as none, the trial is recorded as unmasked; further details about allocation concealment or the practical conduct of randomization are not reported in the registry record.

The setting described in the eligibility information is Oregon Health and Science University hospital. Participants were women with poor prenatal clinic attendance, defined in the summary as fewer than 10 prenatal visits and/or 2 or more missed visits, who wanted an IUD for postpartum contraception and planned a live singleton birth. Mirena and Paragard are listed as device interventions. The record does not describe separate outcome results by device, nor does it report how the two devices were assigned or distributed.

The registry lists enrollment of 33 and gives group counts of 17 for immediate postplacental insertion and 16 for insertion at 6 weeks postpartum. The primary completion date is 2017-01-31, the start date is 2014-09, and the current record status is terminated. A reason for termination is not reported in the registry record. The original sample-size justification, recruitment targets, and any changes to planned enrollment are also not reported in the registry record.

The only listed outcome is the proportion of participants with an IUD at 3 months postpartum. Participants were contacted at that time, and the outcome description refers to those who report having an IUD in place. There are no secondary outcomes posted and no analyses listed in the registry. Details on follow-up completion, analysis populations, protocol deviations, or the statistical plan are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

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 Proportion of Subjects With an IUD at 3 Months Postpartum, measured over 3 months postpartum (after delivery).

The primary endpoint is the proportion of participants who reported having an IUD in place at 3 months postpartum. The registry describes contacting participants at 3 months after delivery and comparing those assigned to immediate insertion within 60 minutes of placental delivery with those assigned to insertion at the routine 6-week postpartum visit. The outcome is recorded as a participant count in each group: 12 of 17 in the immediate group and 5 of 16 in the 6-week group.

This endpoint addresses whether an IUD was reported to be in place at a specified follow-up point. It is used to compare the two assigned timing strategies on a directly interpretable binary outcome: whether the participant reported an IUD in place or did not. A group proportion can communicate the observed frequency of that outcome, while a contrast between groups describes how those frequencies differ. The registry’s description does not establish the device’s duration in place, reasons for not having an IUD, or whether participants experienced other outcomes. It also does not say whether IUD status was verified through clinical examination or records; that ascertainment detail is not reported in the registry record. Thus, interpretation should remain focused on reported IUD presence at the stated follow-up, rather than extending to outcomes the endpoint does not measure.

7. Results Posted in the Registry

• 6 Weeks Postpartum IUD Insertion: 31.2% (5/16) versus 70.6% (12/17) on control; risk difference -39.3 percentage points (95% CI -70.7 to -8.0), risk ratio 0.44 (0.20–0.97); unadjusted two-proportion z-test p = 0.024.

8. Statistical Interpretation

9. Statistical Methods Explained

The reported primary comparison concerns a binary outcome: a participant either was counted as reporting an IUD in place at 3 months postpartum or was not. The group counts are 12 of 17 for immediate postplacental insertion and 5 of 16 for insertion at 6 weeks postpartum. The registry also gives group proportions as 0.706 and 0.312, respectively. A difference in proportions expresses the contrast on the same scale as the outcome: positive values would indicate a higher proportion in the first group named in the comparison, and negative values indicate a lower proportion in that group. The registry’s comparison is oriented as 6-week insertion relative to immediate insertion, with a risk difference of -0.393.

What does the risk difference describe?

In general, a risk difference subtracts one group’s event proportion from the other group’s event proportion. It is an absolute contrast, not a relative one. Here, the stated direction is the 6-week group compared with the immediate group. The negative estimate therefore corresponds to a lower observed proportion in the 6-week group. This interpretation depends on preserving the comparison direction; reversing the group order would reverse the sign. The estimate is an observed group contrast, not a statement about each individual participant’s outcome.

How should the p-value be read?

The registry lists an unadjusted p-value of 0.024 for the comparison. In general, a p-value describes how unusual results at least as incompatible with a specified null model would be if that model and the analysis assumptions held. It is not the probability that the groups are truly identical, nor does it measure the size of the difference. Because the record does not describe the exact test or the analysis plan, no particular test should be attributed to the trial. The unadjusted result also does not account for a multiplicity procedure; no such procedure is reported in the registry record.

The risk difference is accompanied by a confidence interval from -0.707 to -0.080. In general, a confidence interval represents uncertainty in an estimated contrast under the method used to construct it. Its range conveys more about estimation precision than a point estimate alone. It does not mean that every value in the interval is equally plausible, and its interpretation relies on the statistical procedure and assumptions behind the calculation. Those procedures are not specified in the registry record.

What do relative measures add?

The comparison also includes a risk ratio of 0.443 with an interval from 0.201 to 0.974, and an odds ratio of 0.189 with an interval from 0.043 to 0.836. These are relative measures, which express a contrast as a ratio rather than as an absolute difference. Their values depend on the same group ordering used for the comparison. A risk ratio compares proportions directly; an odds ratio compares event odds. These measures are not interchangeable, particularly when event proportions are not small. Since the primary endpoint is a binary event and the sample is limited, the absolute risk difference and its interval offer a direct way to express the observed group contrast, while the relative measures provide alternative scales rather than independent evidence.

General statistical context: estimates from small groups can be sensitive to the outcomes of a small number of participants. Random allocation supports a comparative design, but it cannot remove uncertainty in the estimate. The record’s lack of masking, limited enrollment, and unreported information about missing outcomes and analysis populations should be considered when assessing how much weight to place on the numerical comparison. Whether those factors affected the result cannot be determined from the registry record.

What is not documented about the analysis?

The registry lists no analyses and does not report a statistical analysis plan, the specific test used for the primary comparison, covariate adjustment, handling of missing outcomes, or definitions of analysis populations. It also does not report interim analyses or a plan for multiple comparisons. These details affect interpretation and reproducibility: for example, different analysis choices can produce different estimates or uncertainty intervals, especially when data are sparse. Their absence means that the posted numerical results can be described, but the exact analytic pathway cannot be reconstructed from the registry record.

The comparison is not described as adjusted for other variables. That does not establish whether adjustment was absent from every study document; it means only that adjustment details are not reported in the registry record. In general, an adjusted analysis estimates a contrast conditional on specified variables, whereas an unadjusted comparison uses the observed group data without such conditioning. The listed group counts and unadjusted p-value should therefore be distinguished from any unreported analysis that may have been planned or conducted elsewhere.

Finally, the endpoint is based on participant reports following contact at 3 months postpartum. In general, outcome ascertainment can affect a binary result if some participants are not reached or if reporting differs from the underlying status. The registry does not give contact completion, verification procedures, or missing-data methods. It is therefore not possible to determine whether the counts represent complete follow-up, or how any unavailable responses were treated. These are not merely technical details: they define which information contributes to the estimate and what population the result describes.

10. Confidence Intervals and Precision

The risk-difference estimate for insertion at 6 weeks compared with immediate postplacental insertion is -0.393, with a confidence interval from -0.707 to -0.080. The interval includes values representing a smaller negative contrast as well as values representing a larger negative contrast. It expresses uncertainty around the point estimate; it does not guarantee that the true contrast falls within these particular limits for this trial.

In general, a confidence interval is a range produced by a statistical procedure that, under its assumptions, reflects the uncertainty associated with estimating a population quantity from a sample. A narrower interval indicates greater precision on the scale being estimated, while a wider interval indicates less precision. Precision is distinct from whether an estimate is important or whether a statistical test crosses a threshold. The exact method used to construct this interval is not reported in the registry record, so its assumptions cannot be checked from the registry entry alone.

The group counts are 17 and 16, and the outcome counts are 12 and 5. With group sizes of this scale, the interval is an important part of interpreting the comparison: the point estimate alone gives an incomplete picture of the range of values compatible with the data under the interval method. The risk-ratio interval, 0.201 to 0.974, and odds-ratio interval, 0.043 to 0.836, also communicate uncertainty on their respective relative scales. These intervals are not directly comparable in width with the risk-difference interval because they use different scales.

Precision concerns estimation of the reported group contrast. It does not address follow-up completeness, outcome measurement, representativeness, or whether the result would recur in a different setting. Those issues are not resolved by a confidence interval.

11. 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 sample-size display is a planning illustration based on the observed effect, not the trial’s original design calculation. Its figures are participants per arm, rather than total participants or total events. It uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect: 100%, 75%, or 50%.

For the 100% of the observed effect scenario, the display gives 25 participants per arm for 80% power and 32 participants per arm for 90% power. For planning for 75% of the observed effect, it gives 44 participants per arm for 80% power and 58 participants per arm for 90% power. For planning for 50% of the observed effect, it gives 96 participants per arm for 80% power and 128 participants per arm for 90% power.

In general, power is the probability that a planned study will detect an effect of the specified size under the assumptions used, if that effect is present. The 80% power column and 90% power column therefore describe alternative planning targets: the latter aims for a higher chance of detecting the chosen effect, with the listed participant requirements. Smaller effects need more participants to detect under the same planning framework, as the figures for the smaller fractions illustrate.

These figures are not observed power and should not be read as an assessment of the completed trial’s chance of detecting its result. They are illustrative projections from the observed effect and the listed assumptions. The trial’s own original sample-size assumptions and justification are not reported in the registry record.

12. 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 = 0.706; treatment proportion p₁ = 0.312; average p̄ = 0.509.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.7070 = 1.3857.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6500 = 0.5470.
4. n = (1.3857 + 0.5470)² / (-0.3934)² = 24.1, rounded up to 25 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 <- 0.705882352941177                          # control proportion
p1 <- 0.3125                          # 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(2169869)
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 = 25 (80% power), 32 (90% power)
 75% of observed effect: n per arm = 44 (80% power), 58 (90% power)
 50% of observed effect: n per arm = 96 (80% power), 128 (90% power)
power.prop.test: 24.1 
Simulated power at n = 25 per arm: 0.848 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, the proportion of participants with an IUD at 3 months postpartum, and no secondary outcomes are posted. It lists no analyses. A multiplicity adjustment or strategy for controlling the chance of false-positive findings across multiple planned comparisons is not reported in the registry record. The unadjusted p-value of 0.024 should therefore be read as an unadjusted result; the record does not establish whether other comparisons were planned or conducted outside the posted information.

Missing outcome information is another uncertainty. The endpoint description says participants were contacted at 3 months after delivery, but the registry does not report how many were reached, whether any responses were unavailable, or how unavailable outcomes were handled. It also does not state whether the reported group counts represent all randomized participants or a subset with available outcome information. No imputation, missing-data sensitivity analysis, or other missingness strategy is reported in the registry record. The observed counts can be described, but follow-up completeness cannot be inferred from them.

The registry does not define analysis populations, such as whether the primary analysis followed randomized assignment regardless of treatment received or included only participants who received the assigned insertion timing. The randomization is described as occurring after delivery, but details about treatment receipt, crossover, or protocol deviations are not given. Consequently, the exact population represented by the primary comparison cannot be determined beyond the listed group counts and outcome description.

The statistical analysis plan, covariate adjustment, interim analyses, and rules for selecting among outcomes are not reported in the registry record. These omissions limit assessment of whether the posted result follows a prespecified analytic approach. They do not prove that such procedures were absent from study conduct; they mean the registry entry does not document them. Any interpretation of statistical significance should therefore remain tied to the unadjusted comparison and the information actually recorded.

14. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry lists serious adverse events as zero in the immediate postplacental group, with 17 participants at risk, and zero in the 6-week postpartum group, with 16 participants at risk. It also lists zero other adverse events in each group, with the same respective numbers at risk, and zero deaths in both groups. No serious adverse event terms are listed.

These figures indicate that no events in the listed categories were recorded for the groups in the registry entry. They should not be interpreted as proof that the underlying risk is zero. A small number of participants and the absence of detail about event collection, follow-up completeness, and definitions limit what can be concluded from zero recorded events. The registry does not provide descriptions of surveillance procedures or additional safety analyses, so those details are not reported in the registry record.

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

The posted results describe a higher observed proportion reporting an IUD in place at 3 months postpartum in the group assigned to immediate postplacental insertion than in the group assigned to insertion at 6 weeks postpartum. The primary contrast is reported as a risk difference of -0.393 for the 6-week group relative to the immediate group, with a confidence interval from -0.707 to -0.080 and an unadjusted p-value of 0.024. The group counts were 12 of 17 and 5 of 16, respectively.

This is a result from a randomized, unmasked trial with enrollment of 33, conducted among patients described as having poor prenatal clinic attendance and wanting postpartum IUD contraception at a single hospital setting. The result concerns the specific endpoint of reported IUD presence at 3 months after delivery. It does not answer every question about device use or outcomes, and it does not establish why participants did or did not have an IUD at follow-up.

The finding does not, on its own, establish that the same difference would appear in other populations or settings. The limited group sizes leave uncertainty around the magnitude of the contrast. The registry does not report whether follow-up was complete, how missing outcomes were handled, or the detailed analysis plan. The record is marked terminated, and the reason is not reported in the registry record. Those features constrain how broadly or confidently the result can be interpreted.

The displayed result also should not be treated as a complete account of safety or of every consequence of either timing strategy. The adverse-event entries report zero serious and other adverse events and zero deaths, but the registry does not detail surveillance or completeness. The outcome data and safety entries are descriptive evidence from this trial, not a basis for medical advice or a recommendation about an individual’s care.

16. Why This Trial Matters Statistically

This trial presents a useful statistical example of how a randomized comparison can yield a clear observed difference while still leaving substantial uncertainty about its size and generalizability. The primary endpoint is binary and directly tied to a defined follow-up time: whether participants reported an IUD in place at 3 months postpartum. The contrast is understandable on an absolute scale through the risk difference, while the confidence interval makes visible the uncertainty that a point estimate alone would hide.

The small groups make the relationship between sample size and precision especially relevant. The posted counts are 17 and 16 participants, and the comparison interval spans a range of possible risk differences. A p-value is one part of the statistical description, but it does not replace the estimate, its interval, or careful attention to how outcomes were collected. Readers can distinguish the size of the observed contrast from the uncertainty around it and from questions the analysis does not resolve.

The registry also illustrates why reporting details matter. Information about missing outcomes, analysis populations, the exact statistical method, and the original sample-size justification is not reported in the registry record. Such details help readers understand how participants and outcomes contributed to an estimate and whether the analysis matched the planned approach. The record’s terminated status without a reported reason adds context that cannot be resolved by the numerical results alone.

For biostatisticians and clinical researchers, the key statistical lesson is to read the randomized comparison, outcome definition, point estimate, interval, and reporting gaps together. A numerical contrast can be informative without being definitive, and statistical significance does not substitute for assessment of precision, measurement, and applicability.

17. 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 trial’s enrollment was 33, with 17 participants in the immediate group and 16 in the 6-week group. These group sizes limit the amount of information available for estimating the primary contrast and make the confidence interval an important part of interpretation. The registry marks the study as terminated, but the reason for termination is not reported in the registry record; its effect on recruitment or study conduct cannot be assessed.

The study is recorded as having no masking. The endpoint is based on participants reporting whether they had an IUD in place after contact at 3 months postpartum. The registry does not report whether that status was independently verified, how many participants were reached, or how missing responses were handled. These gaps make it difficult to assess outcome ascertainment and follow-up completeness.

The population was narrowly described by prenatal attendance, desire for an IUD, and planned delivery at Oregon Health and Science University hospital. That setting and eligibility description may limit how directly the results apply to other groups or care settings; the registry does not provide evidence to quantify any difference in applicability. Mirena and Paragard are listed, but device-specific use and results are not reported in the registry record.

The registry has no posted secondary outcomes or analyses and does not report a statistical analysis plan, analysis populations, adjustment strategy, interim analyses, or original sample-size justification. The exact method used for the primary interval and p-value is also not reported. These limitations restrict assessment of reproducibility and of whether the posted analysis followed a prespecified plan.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Immediate Postplacental IUD Insertion — NCT02169869.
• Registry record last updated 2019-05-01; status last verified 2019-04.
• Results first posted 2019-05-01.
• 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.

21. Record Summary

NCT02169869 is a randomized, parallel-group, unmasked trial of immediate postplacental IUD insertion versus insertion at the routine 6-week postpartum visit. The registry describes enrollment of women with poor prenatal clinic attendance who wanted postpartum IUD contraception and planned a live singleton birth at Oregon Health and Science University hospital. Enrollment is listed as 33, and the study status is terminated.

The only listed outcome is the proportion reporting an IUD in place at 3 months postpartum. The record lists 12 of 17 participants in the immediate group and 5 of 16 in the 6-week group. The reported risk difference for the 6-week group compared with the immediate group is -0.393, with a confidence interval from -0.707 to -0.080 and an unadjusted p-value of 0.024. No secondary outcomes or analyses are listed. The reason for termination and several details needed to assess follow-up and analysis are not reported in the registry record.