Hospital Waterbirth Trial to Measure Maternal and Neonatal Outcomes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Hospital Waterbirth Trial to Measure Maternal and Neonatal Outcomes (NCT05175599), a randomized na study. The primary outcome is Number of Women Using Intravenous Narcotic Analgesia and Epidural Anesthesia.

2. Clinical Question

The trial asks whether outcomes differ between two hospital birth approaches for the population described in the registry. Its stated hypothesis included less pain medication use, shorter labor, more breastfeeding initiation before discharge, no increase in negative outcomes, and greater satisfaction in the waterbirth group. These are proposed expectations, not findings. The primary posted endpoint is specifically the number of women using intravenous narcotic analgesia and epidural anesthesia; it does not by itself answer every part of that broader hypothesis.

The comparison is between groups assigned to waterbirth or land birth, but the primary outcome population is described as women who remained eligible at delivery. That qualification matters when interpreting the counts: the registry does not describe the full analysis population or explain how women who were no longer eligible were handled. The question answered by the posted primary numbers is therefore narrower than a claim about every participant enrolled in the trial.

Waterbirth and land birth represent distinct care approaches in the study description. The reported outcome is about analgesia use, not a direct measure of pain, labor experience, satisfaction, or the safety of either approach. Other listed outcomes address some of those broader interests, but numerical results for most of them are not reported in the registry record.

3. Trial Design

The registry describes a randomized, parallel-group study with no masking. The official title identifies it as a pilot randomized control study. The record gives an enrollment of 186 and lists the study status as completed. The study start date is 2022-01-17, and the primary completion date is 2023-12-23. Wake Forest University Health Sciences is listed as the sponsor.

Participants were assigned to a waterbirth or land birth group. The land birth group followed standard of care procedures for labor and birth. The waterbirth group gave birth in water, with the option to enter or leave the water during the first stage of labor. The study summary describes the setting as a hospital in Milwaukee, WI and the intended population as low-risk healthy women and neonates.

Random allocation is intended, in general, to make the groups comparable at the point of assignment, including with respect to factors that may affect outcomes. The registry does not report the randomization sequence method, allocation concealment, or other details about how assignment was implemented. With no masking listed, the record does not indicate that participants or care providers were masked to group assignment. It does not report whether outcome assessors were masked.

The primary outcome results use 32 participants in the land birth group and 74 in the waterbirth group. The registry separately reports adverse-event populations at risk of 62 for land birth and 124 for waterbirth. Those outcome denominators differ from the primary outcome denominators; the reasons for the differences are not reported in the registry record. The record does not explain the flow from enrollment to the reported outcome populations, so the enrollment figure should not be treated as the denominator for every outcome.

The registry lists eight outcome measures and seven secondary outcomes. Numerical results are posted for the primary outcome and for breastfeeding and skin-to-skin contact among the secondary outcomes. Numerical results for the other listed secondary outcomes are not reported in the registry record. The trial's original sample-size justification and detailed design assumptions 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.

Before assignment: Upon enrollment, participants were randomized to either the waterbirth group or land birth group using a computer-generated allocation sequence. When participants presented to the labor and delivery until, both groups were reassessed for eligibility. If they remained eligible, those in the waterbirth group received routine care, all available pain relief options, with the additional option of giving birth in the water. Land birth were not given option of birth in the water.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Numbers based on those who remained eligible at time of delivery.

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: Numbers based on those who remained eligible at time of delivery.

6. Primary Endpoint

The registry lists the primary outcome as Number of Women Using Intravenous Narcotic Analgesia and Epidural Anesthesia, measured over Time of admission to birth of the baby.

The primary endpoint is the number of women using intravenous narcotic analgesia and epidural anesthesia, measured from admission to birth of the baby. The registry describes the comparison as the number of women in the waterbirth cohort who use IV narcotic and epidural anesthesia compared with the land birth cohort. It reports counts among those who remained eligible at the time of delivery.

This endpoint is used to address the study's question about pain medication use across the two birth groups. A count of participants with the outcome is a binary-outcome summary: each participant is classified according to whether the recorded event occurred. The registry reports 26 of 32 in the land birth group and 26 of 74 in the waterbirth group. The posted comparison expresses the group contrast as a risk difference, alongside a confidence interval and an unadjusted p-value.

The endpoint should be interpreted according to its recorded definition. It is not a continuous measure of medication dose, timing, pain intensity, or the participant's overall experience. The description refers to intravenous narcotic analgesia and epidural anesthesia together, but the registry record does not explain whether the count includes women who used either type, both types, or a particular combination. That operational detail is not reported in the registry record.

In general, selecting an endpoint makes a broad research question measurable, but the endpoint captures only the specified outcome. The primary measure can inform the comparison of recorded analgesia use between groups; it cannot alone establish whether labor was shorter, satisfaction was higher, breastfeeding differed, or adverse outcomes were similar. Those questions require their own outcome definitions and results.

7. Results Posted in the Registry

• Water Birth: 35.1% (26/74) versus 81.2% (26/32) on control; risk difference -46.1 percentage points (95% CI -63.5 to -28.8), risk ratio 0.43 (0.30–0.61); unadjusted two-proportion z-test p = <0.001.

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.

Number of Patients Breastfeeding

• 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:
  • Water Birth: 90.5% (67/74) versus 93.8% (30/32) on control; risk difference -3.2 percentage points (95% CI -13.9 to 7.5), risk ratio 0.97 (0.86–1.08); unadjusted two-proportion z-test p = 0.586.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Water Birth and the control. The interval gives the range of effects that remain compatible with the data.

Number of Patients With Skin-to-skin Contact

• 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:
  • Water Birth: 91.9% (68/74) versus 84.4% (27/32) on control; risk difference 7.5 percentage points (95% CI -6.5 to 21.6), risk ratio 1.09 (0.92–1.28); unadjusted two-proportion z-test p = 0.244.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Water Birth and the control. The interval gives the range of effects that remain compatible with the data.

The two secondary outcomes with numerical results have estimates in opposite directions. The breastfeeding risk-difference estimate is -0.032, while the skin-to-skin contact estimate is 0.075. Both confidence intervals include zero, and their unadjusted p-values are 0.586 and 0.244. The posted results therefore do not give a clear, precise pattern of secondary differences that reinforces the primary result. They also do not establish that the groups were equivalent on these outcomes.

These outcomes concern different aspects of care from the primary analgesia measure. Breastfeeding through hospital discharge and skin-to-skin contact within the recorded timeframe cannot be treated as substitutes for medication use, labor duration, satisfaction, or adverse outcomes. Their estimates offer outcome-specific information, but they do not answer the broader study hypothesis as a whole. In general, findings across distinct outcomes may differ because the outcomes measure different experiences, are observed in different populations, and have different levels of precision.

The registry lists other secondary outcomes, including labor duration, birth satisfaction, maternal and neonatal adverse outcomes, and instrumental and cesarean deliveries. Numerical results for these outcomes are not reported in the registry record. They cannot be used to support or contradict the primary result on the basis of this record.

Unadjusted secondary results carry less weight when several outcomes are examined because each additional test creates another opportunity for an apparently notable result to arise from random variation. The registry does not report a multiplicity strategy or identify which secondary outcomes, if any, were prespecified as confirmatory. These results are best treated as descriptive and exploratory rather than as independent confirmation of the primary comparison. The primary finding remains a result about the specified analgesia endpoint; secondary observations should not be combined into a general conclusion about the birth approaches.

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

• Median Time of Labor Duration
• United States Birth Satisfaction Scale-Revised (US-BSS-R) Score
• Number of Reported Maternal Adverse Outcomes
• Number of Patients Breastfeeding
• Number of Neonatal Adverse Outcomes
• Number of Patients With Neonates With Instrumental and Cesarean Deliveries
• Number of Patients With Skin-to-skin Contact

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports participant counts for the primary outcome and secondary outcomes that have numerical results. The primary measure is binary: a participant either was or was not counted as using the specified analgesia outcome. In general, binary outcomes can be summarized as a count and a proportion within each group. The posted comparison uses a risk difference, which expresses the difference between the groups' observed proportions. The sign of the difference depends on the order of subtraction; in this record, the waterbirth group is compared with land birth, and a negative estimate indicates a lower observed proportion in the waterbirth group.

What does the risk difference describe?

A risk difference is an absolute contrast on the proportion scale. In general, it is useful because it describes how far apart the observed proportions are, rather than expressing the contrast as a relative multiple. The primary posted risk difference is -0.461. The arm-level proportions are 0.812 for land birth and 0.351 for waterbirth. These are the values reported for the groups; no additional calculations are needed to interpret the direction. The estimate does not adjust for other variables, and the registry does not report an adjusted estimate.

The record also presents relative measures for the primary result: a risk ratio of 0.432 with interval limits 0.304 and 0.615, and an odds ratio of 0.125 with interval limits 0.046 and 0.343. In general, a risk ratio compares proportions as a relative quantity, while an odds ratio compares odds. These measures use different scales and should not be read as interchangeable. The registry does not identify a separate adjusted analysis for either measure.

How should confidence intervals be understood?

In general, a confidence interval describes the uncertainty around an estimated contrast under a specified statistical method. It gives a range of values that are compatible with the observed data and the method's assumptions at the stated confidence level. It is not a guarantee that the true value lies in the interval, and it does not describe the range of outcomes for individual participants. A narrower interval indicates more precision on that scale; a wider interval indicates greater uncertainty.

The primary risk-difference interval runs from -0.635 to -0.288. For the breastfeeding result, it runs from -0.139 to 0.075; for skin-to-skin contact, it runs from -0.065 to 0.215. The secondary intervals include zero. That means the posted estimates do not rule out a zero risk difference at the interval's stated confidence level, but it also does not prove there is no difference. For the primary outcome, the interval is entirely below zero, with the direction favoring a lower observed proportion in the waterbirth group for this endpoint.

What does the p-value add?

The primary comparison has an unadjusted p-value of <0.001. The breastfeeding and skin-to-skin comparisons have unadjusted p-values of 0.586 and 0.244. In general, a p-value measures how well the observed data fit a null model of no group difference, assuming the statistical test and its conditions apply. It is not an effect-size measure, does not measure clinical importance, and does not quantify the probability that a finding is due to chance. Because the secondary p-values are unadjusted, they do not account for the fact that several outcomes are considered.

The registry does not report the exact statistical test used for the posted comparisons, any covariate adjustment, or detailed model specifications. The p-values and intervals should therefore be interpreted as the posted unadjusted comparisons rather than as evidence for a more elaborate analysis. The record lists no separately reported secondary analysis records.

Why can over-dispersion matter?

In general, over-dispersion means that observed variability is greater than expected under a model's assumptions. It matters for outcomes modeled as counts or rates because a model that understates variability can produce intervals that are too narrow and p-values that are too small. The outcomes reported with numerical results in this record are participant counts for binary events, not repeated event rates or continuous measures. The registry does not report a dispersion estimate or an over-dispersion adjustment; none should be inferred from the posted counts.

These methods describe contrasts in the recorded groups. Statistical significance does not by itself establish that a finding is important to participants, that assignment caused every observed difference, or that the result applies to populations beyond those described. Interpretation also depends on how outcomes were defined, who was included in each analysis, and how missing outcomes were handled. Those details are not reported in the registry record.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.461, with a 95% confidence interval from -0.635 to -0.288. The entire interval is below zero, so the posted comparison is directionally consistent with a lower observed proportion of the analgesia outcome in the waterbirth group. The interval still spans a range of possible magnitudes; it should not be reduced to a single definitive value. Its limits reflect sampling uncertainty under the method used, not all possible sources of bias or uncertainty about the outcome definition.

The primary groups have reported denominators of 32 for land birth and 74 for waterbirth. In general, precision depends on the amount of information in the data, the observed event proportions, and the statistical method. The registry does not explain why these are the primary analysis denominators or how the eligibility-at-delivery population was formed. The confidence interval therefore does not resolve uncertainty about selection into the analyzed population or missing outcome information.

The secondary confidence intervals are wider relative to their estimates and cross zero: -0.139 to 0.075 for breastfeeding and -0.065 to 0.215 for skin-to-skin contact. Those intervals allow for group differences in either direction, as well as values near zero. Their unadjusted p-values are 0.586 and 0.244. The data do not support treating these outcomes as proven equivalent, nor do they provide precise evidence for a specific directional effect.

A confidence interval describes statistical precision only within the framework of the analysis. It does not account automatically for multiple outcome testing, unreported analysis choices, measurement limitations, or differences between enrolled participants and the analyzed outcome populations. The registry does not report methods for missing data, multiplicity, or adjusted analyses. Those omissions are relevant when judging how much confidence to place in a result beyond the interval's sampling uncertainty.

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 estimates are illustrations based on the observed effects, not the trial's original sample-size plan. For these binary participant outcomes, the figures are participants per arm, not total events. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect: 100%, 75%, or 50%. The registry's own original sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the illustrated number of participants per arm for a planning scenario with an 80% chance of detecting the specified effect under the stated assumptions, if that effect were the true effect and the planning model were appropriate. The 90% power column gives the corresponding planning number for a higher chance of detection. These are planning quantities, not guarantees: actual power can differ if the true effect, event proportions, allocation, analysis, or data completeness differ from the assumptions.

For each outcome, the displayed estimates are larger when the target is a smaller fraction of the observed effect. This follows a general statistical principle: smaller differences are harder to distinguish from random variation, so detecting them at the same planned power generally requires more participants. The estimates are based on the observed trial contrasts, which may themselves be uncertain, particularly when outcome denominators are limited.

These figures are not observed power. They do not measure the probability that the completed study detected an effect after seeing its results, and they should not be used to characterize the trial's original design because the registry does not report that design calculation. They are conditional planning illustrations for future study sizing under the stated assumptions. The equal-allocation assumption also differs from the reported primary outcome group sizes, so the illustration should be read as a planning scenario rather than a description of the completed enrollment pattern.

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 = 0.812; treatment proportion p₁ = 0.351; average p̄ = 0.582.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6976 = 1.3672.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6166 = 0.5190.
4. n = (1.3672 + 0.5190)² / (-0.4611)² = 16.7, rounded up to 17 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 <- 0.8125                          # control proportion
p1 <- 0.351351351351351                          # 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(5175599)
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 = 17 (80% power), 22 (90% power)
 75% of observed effect: n per arm = 30 (80% power), 39 (90% power)
 50% of observed effect: n per arm = 62 (80% power), 82 (90% power)
power.prop.test: 16.7 
Simulated power at n = 17 per arm: 0.827 (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 lists a primary outcome and several secondary outcomes, but it does not report a procedure for handling multiple comparisons. Multiplicity arises when more than one outcome or hypothesis is tested: the chance of at least one apparently unusual result can increase as the number of tests grows. In general, statistical approaches can control or otherwise address that issue, but the appropriate method depends on the study's aims and analysis plan. No such method is reported in the registry record.

The posted p-values are identified as unadjusted. The primary p-value is <0.001; the secondary p-values reported for breastfeeding and skin-to-skin contact are 0.586 and 0.244. Without a reported multiplicity plan, the secondary p-values should not be treated as a family of confirmatory tests with a known overall error rate. The record also does not report whether the primary outcome was designated as the sole confirmatory endpoint in the analysis plan, although it is labeled as the primary outcome.

Missing-data handling is not reported in the registry record. There is no reported method for handling participants without an outcome measurement, no account of missingness by group, and no sensitivity analysis described. The primary endpoint is based on participants who remained eligible at the time of delivery, but the registry does not explain how eligibility was determined or how participants outside that population were handled. The reasons that the primary outcome denominators differ from enrollment are also not reported.

The analysis population is not fully described. The registry does not state whether the primary comparison followed an intention-to-treat approach, was restricted to participants who received the assigned birth approach, or used another population definition. It does not report an analysis plan specifying how deviations from assigned group or changing eligibility were treated. Those methods should not be inferred from the randomization label or from the posted counts.

Interim analyses, stopping rules, covariate adjustment, and detailed statistical procedures are not reported in the registry record. Their absence from the record does not establish that a procedure was or was not used; it means the relevant information is unavailable for interpreting the posted results. These gaps limit assessment of prespecification and analysis choices, especially for the multiple secondary outcomes.

15. 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.

Most frequent non-serious adverse event terms

The registry reports serious adverse events for 62 participants at risk in the land birth group and 124 at risk in the waterbirth group. The recorded number with a serious adverse event is 0 in each group. Deaths are reported as 0 in both groups. These figures describe the events recorded in the listed populations at risk during the registry's reporting period; they do not show that the groups have identical risk.

For other adverse events, the registry reports 5 affected participants among 62 at risk in the land birth group and 12 among 124 at risk in the waterbirth group. These are counts, not adjusted comparisons. The record does not provide a detailed breakdown of the other adverse-event terms in the information, and the serious-event terms list is empty.

The adverse-event populations at risk differ from the primary outcome denominators. The registry does not explain the reason for that difference, so the safety counts should not be treated as if they used the primary endpoint population. In general, observing no serious events in a study does not establish that a serious event cannot occur or that two groups have equivalent safety. The amount of information and the scope of event collection matter, and the record does not provide enough detail to evaluate those issues fully.

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

The primary posted comparison shows a lower observed proportion of women counted with the analgesia outcome in the waterbirth group than in the land birth group. The estimate is a risk difference of -0.461, with a 95% confidence interval from -0.635 to -0.288 and an unadjusted p-value of <0.001. This describes the registry's reported data for participants who remained eligible at delivery. It does not, by itself, establish the cause of the difference or explain which aspects of care produced it.

The primary endpoint is narrower than the trial's overall hypothesis. It does not measure labor duration, birth satisfaction, breastfeeding, or neonatal and maternal outcomes. The secondary numerical results available for breastfeeding and skin-to-skin contact have confidence intervals that include zero. That means their estimates are uncertain and compatible with differences in either direction; it does not prove that those outcomes are the same between groups. Numerical results for the other listed secondary outcomes are not reported in the registry record.

These results do not establish that waterbirth is appropriate for every pregnancy, that it is safer or less safe overall, or that the findings apply to settings or populations beyond the low-risk healthy women and neonates described in the record. The study summary identifies a hospital setting in Milwaukee, WI. The registry does not report the details needed to assess broader applicability, such as the characteristics of participants who were excluded from the outcome populations or the reasons they were not represented in the reported denominators.

Randomization is an important design feature for comparing assigned groups, but the outcome population definition and missing-data handling remain relevant. The primary endpoint applies to those who remained eligible at delivery, and the registry does not report how that population was formed. As a result, the posted comparison should be understood as an estimate within the reported analysis population, not as a complete account of outcomes among every enrolled participant.

Statistical evidence and clinical importance are different questions. A p-value and confidence interval describe the comparison's statistical compatibility and precision under the analysis assumptions; they do not determine whether the observed difference is important to participants or clinicians. No medical advice follows from these registry results. They are a record of outcome counts and unadjusted statistical contrasts, with important details of the analysis plan and outcome populations not reported.

17. Why This Trial Matters Statistically

This trial raises statistical issues common in clinical research: how to interpret a randomized comparison when the analyzed population is narrower than the enrolled population, how to distinguish a primary endpoint from a broad set of secondary outcomes, and how much confidence to place in estimates with different levels of precision. The record reports random allocation, but the primary outcome population is limited to participants who remained eligible at delivery. Clear definitions of eligibility and analysis populations are important for understanding what a randomized comparison estimates.

The primary result is presented as an absolute risk difference, with a confidence interval and an unadjusted p-value. This makes the estimated direction and uncertainty visible rather than leaving interpretation to the arm counts alone. At the same time, the record does not report the statistical test, adjustment methods, or missing-data procedures. Transparent reporting of those choices would help readers assess the strength and scope of the comparison.

The secondary outcomes illustrate why estimates should be considered together with their uncertainty and their place in the analysis plan. The posted secondary intervals include zero, and the p-values are unadjusted. Without a stated multiplicity approach, these outcomes are more appropriately read as descriptive observations than as a set of confirmatory claims. The other listed secondary outcomes do not have numerical results reported in the registry record, limiting evaluation of the broader hypotheses.

The planning illustrations also demonstrate a general design principle: the number of participants needed depends on the size of the effect a future study aims to detect and the assumptions used for planning. Their assumptions are stated, but they are not the trial's original design justification. Keeping planning calculations distinct from the completed study's observed results prevents a common misinterpretation of power calculations.

Overall, the record offers a useful example of why statistical interpretation requires more than a significant primary p-value. Effect estimates, interval precision, population definitions, secondary testing, and transparent reporting all shape what can reasonably be concluded from a clinical trial record.

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.

The primary outcome is defined for women who remained eligible at the time of delivery, and the registry does not report how that eligibility was determined or how it affected inclusion in the analysis. The primary arm denominators are 32 and 74, while enrollment is 186. The record does not explain the flow from enrollment to those outcome populations. This makes it difficult to assess whether the reported comparison represents all randomized participants or a selected subset.

The adverse-event populations at risk are 62 and 124, which also differ from the primary outcome denominators. The registry does not explain these denominator differences. Readers should therefore avoid assuming that the primary, secondary, and safety outcomes all share the same analysis population or follow-up completeness.

The registry does not report the exact operational definition of the primary analgesia outcome, including whether the count refers to either listed medication type or a combination. It also does not report detailed methods for outcome ascertainment, missing data, analysis populations, covariate adjustment, or multiplicity. No separately reported analysis records are listed for the secondary outcomes. These omissions limit reproducibility and assessment of potential analysis choices.

The record lists several secondary outcomes but gives numerical results for breastfeeding and skin-to-skin contact only. Results for the other listed outcomes are not reported in the registry record, so the broader set of study hypotheses cannot be evaluated from the posted results. The available secondary estimates are unadjusted, and no multiplicity strategy is reported.

The study description concerns low-risk healthy women and neonates in a hospital setting in Milwaukee, WI. Applicability to other populations or settings is uncertain from this record alone. The official title calls the study a pilot, but the registry does not report the original sample-size justification or detailed design assumptions. These limitations do not invalidate the posted numbers; they define the scope and certainty with which they can be interpreted.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Hospital Waterbirth Trial to Measure Maternal and Neonatal Outcomes — NCT05175599.
• Registry record last updated 2026-05-05; status last verified 2025-03.
• Results first posted 2026-05-05.
• 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 record describes NCT05175599, titled “Hospital Waterbirth Trial to Measure Maternal and Neonatal Outcomes,” with the official title “Hospital Waterbirth: A Pilot Randomized Control Study.” It lists Wake Forest University Health Sciences as sponsor, randomized allocation, a parallel design, no masking, enrollment of 186, and completed status. The recorded study start is 2022-01-17, and primary completion is 2023-12-23.

The primary outcome is the number of women using intravenous narcotic analgesia and epidural anesthesia from admission to birth. The posted counts are 26 of 32 for land birth and 26 of 74 for waterbirth, with a risk difference of -0.461 and an unadjusted p-value of <0.001. Numerical secondary results are posted for breastfeeding and skin-to-skin contact; results for the other listed secondary outcomes are not reported in the registry record.

The record reports no serious adverse events or deaths in either listed group at risk. It does not report the original sample-size justification, detailed analysis methods, missing-data procedures, or multiplicity handling. Those omissions and the differing reported outcome denominators are important context for interpreting the estimates.