MAARIE Template for Evaluating Evidence Based Health Research

MAARIE Template for Evaluating Evidence Based Health Research (please use attached template)

Method- The purpose and population for the investigation
1. Study hypothesis
What is the study question being investigated?

2. Study population
What population is being investigated and what are the inclusion and exclusion criteria for the participants of the investigation?

3. Sample size and statistical power
How many individuals are included in the study and in the control groups? Are the numbers adequate to demonstrate statistical significance if the study hypothesis is true (what is the statistical power)?

Assignment- Selection of participants for the study and control groups
1. Process
What method is used to identify and assign individuals or populations to study and control groups?

2. Confounding variables
Are there differences between study and control groups, other than the factor being investigated, that may affect the outcome of the investigation?

3. Masking or blinding
Are the participants and/or the investigators aware of the participants’ assignment to a particular study or control group?

Assessment- Measurement of outcomes or endpoints in the study and control groups
1. Appropriate
Does the measurement of outcomes address the study’s question?

2. Accurate and precise
Is the measurement of outcomes an accurate and precise measure of the phenomenon that the investigators seek to assess?

3. Complete and unaffected by observation
Is the outcome measurement nearly 100% complete and is it affected by the participants’ or the investigators’ knowledge of the study group or control group assignment?

Results- Comparison of outcomes in the study and control groups
1. Estimation
What is the magnitude or strength of the relationship observed in the investigation?

2. Inference
What statistical technique(s) are used to perform statistical significance testing?

3. Adjustment
What statistical technique(s) are used to take into account or control for differences between the study group and the control group that may affect the results?

Interpretation-   Meaning of the results for those included in the investigation
1. Contributory cause   or efficacy
Does the factor being investigated alter the   probability that the disease will occur (contributory cause) or work to   reduce the probability of undesirable outcomes (efficacy)?

2. Harms
Are adverse events that affect the meaning of the results identified?

3. Subgroups and interactions
Do the outcomes in subgroups differ and are there interactions between factors that affect outcomes?

Extrapolation- Meaning for those not specifically included in the investigation
1. To similar individuals, groups, or populations
Do the investigators extrapolate or extend the conclusions to individuals, groups, or populations that are similar to those who participated in the investigation?

2. Beyond the data
Do the investigators extrapolate by extending the conclusions beyond the dose, duration, or other characteristics of the investigation?

3. To other populations
Do the investigators extrapolate to populations or settings that are quite different from those in the investigation?

Rev. 2021

Riegelman, R.K. & Nelson, B.A. (2021). Studying a study & testing a test. Wolters Kluwer.

Bovbjerg, M. L., Cheyney, M., & Everson, C. (January 01, 2016). Maternal and Newborn Outcomes Following Waterbirth: The Midwives Alliance of North America Statistics Project, 2004 to 2009 Cohort. Journal of Midwifery & Women’s Health, 61, 1, 11-20.

Links to an external site.

Bovbjerg_et_al-2016-Journal_of_Midwifery_%26_Women-s_Health (attached)

MAARIE Template for Evaluating Evidence Based Health Research

Method- The purpose and population for the investigation

1. Study hypothesis
What is the study question being investigated?

2. Study population

What population is being investigated and what are the inclusion and exclusion criteria for the participants of the investigation?

3. Sample size and statistical power
How many individuals are included in the study and in the control groups? Are the numbers adequate to demonstrate statistical significance if the study hypothesis is true (what is the statistical power)?

Assignment- Selection of participants for the study and control groups
1. Process
What method is used to identify and assign individuals or populations to study and control groups?

2. Confounding variables
Are there differences between study and control groups, other than the factor being investigated, that may affect the outcome of the investigation?

3. Masking or blinding
Are the participants and/or the investigators aware of the participants’ assignment to a particular study or control group?

Assessment- Measurement of outcomes or endpoints in the study and control groups
1. Appropriate
Does the measurement of outcomes address the study’s question?

2. Accurate and precise
Is the measurement of outcomes an accurate and precise measure of the phenomenon that the investigators seek to assess?

Results- Comparison of outcomes in the study and control groups
1. Estimation
What is the magnitude or strength of the relationship observed in the investigation?

2. Inference
What statistical technique(s) are used to perform statistical significance testing?

3. Adjustment
What statistical technique(s) are used to take into account or control for differences between the study group and the control group that may affect the results?

Interpretation- Meaning of the results for those included in the investigation
1. Contributory cause or efficacy
Does the factor being investigated alter the probability that the disease will occur (contributory cause) or work to reduce the probability of undesirable outcomes (efficacy)?

2. Harms
Are adverse events that affect the meaning of the results identified?

3. Subgroups and interactions
Do the outcomes in subgroups differ and are there interactions between factors that affect outcomes?

Extrapolation- Meaning for those not specifically included in the investigation

1. To similar individuals, groups, or populations

Do the investigators extrapolate or extend the conclusions to individuals, groups, or populations that are similar to those who participated in the investigation?

2. Beyond the data

Do the investigators extrapolate by extending the conclusions beyond the dose, duration, or other characteristics of the investigation?

3. To other populations

Do the investigators extrapolate to populations or settings that are quite different from those in the investigation?

Rev. 2021

Riegelman, R.K. & Nelson, B.A. (2021).
Studying a study & testing a test. Wolters Kluwer.

Bovbjerg, M. L., Cheyney, M., & Everson, C. (January 01, 2016). Maternal and Newborn Outcomes Following Waterbirth: The Midwives Alliance of North America Statistics Project, 2004 to 2009 Cohort.

Journal of Midwifery & Women’s Health,

61,

1, 11-20.

Links to an external site.

Bovbjerg_et_al-2016-Journal_of_Midwifery_%26_Women-s_Health

Journal of Midwifery &Women’s Health www.jmwh.org
Original Research

Maternal and Newborn Outcomes Following Waterbirth:
The Midwives Alliance of North America Statistics Project,
2004 to 2009 Cohort
Marit L. Bovbjerg, PhD, MS, Melissa Cheyney, PhD, CPM, LDM, Courtney Everson, MA, PhD

Introduction: Data on the safety of waterbirth in the United States are lacking.

Methods: We used data from the Midwives Alliance of North America Statistics Project, birth years 2004 to 2009. We compared outcomes of
neonates born underwater waterbirth (n = 6534), neonates not born underwater nonwaterbirth (n = 10,290), and neonates whose mothers
intended a waterbirth but did not have one intended waterbirth (n = 1573). Neonatal outcomes included a 5-minute Apgar score of less than 7,
neonatal hospital transfer, and hospitalization or neonatal intensive care unit (NICU) admission in the first 6 weeks. Maternal outcomes included
genital tract trauma, postpartum hospital transfer, and hospitalization or infection (uterine, endometrial, perineal) in the first 6 weeks. We used
logistic regression for all analyses, controlling for primiparity.

Results:Waterbirth neonates experienced fewer negative outcomes than nonwaterbirth neonates: the adjusted odds ratio (aOR) for hospital trans-
fer was 0.46 (95% confidence interval [CI], 0.32-0.68; P � .001); the aOR for infant hospitalization in the first 6 weeks was 0.75 (95%CI, 0.63-0.88;
P � .001); and the aOR for NICU admission was 0.59 (95% CI, 0.46-0.76; P � .001). By comparison, neonates in the intended waterbirth group
experienced more negative outcomes than the nonwaterbirth group, although only 5-minute Apgar score was significant (aOR, 2.02; 95% CI,
1.40-2.93; P � 0001). For women, waterbirth (compared to nonwaterbirth) was associated with fewer postpartum transfers (aOR, 0.65; 95% CI,
0.50-0.84; P = .001) and hospitalizations in the first 6 weeks (aOR, 0.72; 95% CI, 0.59-0.87; P � 0.001) but with an increased odds of genital tract
trauma (aOR, 1.11; 95%CI, 1.04-1.18; P = .002).Waterbirth was not associated withmaternal infection.Women in the intended waterbirth group
had increased odds for all maternal outcomes compared to women in the nonwaterbirth group, although only genital tract trauma was significant
(aOR, 1.67; 95% CI, 1.49-1.87; P � .001).

Discussion:Waterbirth confers no additional risk to neonates; however, waterbirth may be associated with increased risk of genital tract trauma
for women.
J Midwifery Womens Health 2016;61:11–20 c© 2016 by the American College of Nurse-Midwives.

Keywords: childbirth, complications, perineal trauma, safety,

waterbirth

INTRODUCTION

Waterbirth is highly controversial in the United States,1–8
despite being an accepted practice in other high-resource
nations.9–12 Proponents of waterbirth cite anthropological ev-
idence from Odent and Tjarkovsky regarding childbearing
traditions that include immersion13,14; the maternal benefits
of laboring in water, such as pain relief and reduced stress
on tissues secondary to buoyancy15,16; the potential benefits
to a neonate of being born into a warm, liquid environment
similar to the amniotic fluid17; and a series of studies, mostly
small and observational, suggesting no adverse effects for ei-
ther the laboring woman or the neonate.18,19 By contrast, in
the spring of 2014, the American College of Obstetricians and
Gynecologists (ACOG) and the American Academy of Pedi-
atrics (AAP) jointly issued clinical recommendations advising
strongly against allowing women to labor in water after the
first stage of labor is complete.3

Waterbirth is generally defined as a neonate being in-
tentionally born underwater. Provided that the neonate is

Address correspondence to Marit Bovbjerg, PhD, MS, College of Public
Health and Human Sciences, Oregon State University, Milam Hall 103,
Corvallis, OR 97331. E-mail: marit.bovbjerg@oregonstate.edu

promptly brought to the surface, it is thought that the diving
reflex, which mechanically blocks the airway of submerged
infants (although not older children or adults), will pre-
vent the newborn from aspirating the water.20 The category
waterbirth does not include women who labor in water but
give birth to their newborn into air. Laboring in water is con-
sidered safe; the current question in the literature is whether
waterbirth is safe.3

Published reports of outcomes following waterbirth in the
United States currently consist solely of case series1,2,4,5,21–24
rather than studies with robust designs and adequate power.
However, there are several cohort studies from Europe
describing waterbirth outcomes,25–35 nicely summarized by
Nutter et al in a recent review.19 The results of these studies
collectively suggest that waterbirth is not associated with
an increased risk of morbidity for the newborn (eg, low
Apgar score, neonatal intensive care unit [NICU] admission,
neonatal injury, or death), although small sample sizes hinder
comparisons for all but themost common events.18,19 Regard-
ing maternal outcomes, previous literature suggests women
do not experience an increase in perineal trauma, infection,
or hemorrhage.18,19 Nonetheless, it can be argued that both
the US population and US health care system are unique, and
thus results from Europe might not be generalizable to the

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✦ Using data collected from the Midwives Alliance of North America Statistics Project (MANA Stats 2004-2009), this study
reports waterbirth outcomes for a large sample of midwife-attended births occurring at home and in birth centers in the
United States (N = 18,343 women); 35% of the women (n = 6521 women; 13 sets of twins) had a waterbirth.

✦ Neonates of womenwho had awaterbirth were less likely to experience a low 5-minute Apgar score, neonatal transfer to the
hospital, and hospitalization or neonatal intensive care unit admission in the first 6 weeks when compared to nonwaterbirth
neonates.

✦ For women, waterbirth was associated with decreased odds of hospitalization, either immediately postpartum or within
the first 6 weeks, but increased odds of genital tract trauma.

✦ Waterbirth was not associated with increased risk of maternal infection.

United States. The purpose of this study, therefore, was to re-
port waterbirth outcomes from a large sample of midwife-
led births occurring at home and in birth centers in the
United States.

METHODS

Data Source and Sample Description

The data for this study come from the Midwives Alliance
of North America Statistics Project, commonly referred to
as MANA Stats.36 MANA Stats is an ongoing, Web-based
data collection effort designed to capture complete courses
of care from the medical records of women who have had
midwife-led pregnancies and births. Any midwife, regardless
of birth setting, is eligible to contribute data. However, in
practice, most MANA Stats records are for planned home or
planned birth center births (97.6% for the years 2004-2009)
attended by certified professional midwives (CPMs) in the
United States. Of the births in the 2004 to 2009 MANA Stats
dataset, 73% of the births were attended by CPMs.36

A midwife who is a MANA Stats contributor enters data
on all women in her care from the first prenatal visit through
the final visit, which is usually at 6 weeks postpartum.
Midwives are required to preregister or log patients into the
MANA Stats system early in care, before the outcome of the
pregnancy is known. This prospective logging helps to ensure
that all births from participating midwives are captured,
regardless of outcome, thus reducing selection bias in the
sample.

Women give informed consent allowing their deidentified
data to be included in MANA Stats, and the consent includes
explicit permission for the data to be used for research. Should
a woman decline consent, her data are not included, but this
decision to decline consent would occur early in pregnancy
and thus could not be affected by pregnancy outcome. In prac-
tice, very few women decline this consent; based on practice
data reported bymidwives, we estimate thatMANA Stats cap-
tures 97% of births attended by midwife contributors.36 The
high rate of maternal participation in this population is not
unique to the MANA Stats dataset; it has also been reported
in other studies enrolling women planning home and birth
center births.37,38

The institutional review board at Oregon State University
approved this analysis, which usesMANA Stats data for births

that occurred between 2004 and 2009. Evidence of reliabil-
ity and validity of the MANA Stats 2004 to 2009 dataset,
as well as detailed data collection protocols, is presented
elsewhere.36

We limited our sample to births that were planned home
births or planned birth center births at the onset of labor
wherein the neonate was actually born in the intended set-
ting (ie, no intrapartum transfer to a hospital occurred). Thus,
excluded from the sample were the data from women who
planned a hospital birth and from those for whom a hospital
birth was not planned but occurred following an intrapartum
transfer (Figure 1).

These cases were excluded for 2 reasons. First, during the
research years (2004-2009), very few hospitals in the United
States offered the option of giving birth underwater.39 Second,
hospital births are almost always the most complicated preg-
nancies and labors in the MANA Stats database; the major-
ity of contributors to the project specialize in home or birth
center birth and transfer care to hospitals only when com-
plications arise.40 Thus, including women with more compli-
cated pregnancies or labors resulting in the transfer of care to
a hospital-based provider, either before or during labor, com-
bined with the reduced likelihood of encountering the expo-
sure, would have introduced bias in the direction of making
waterbirth appear safer relative to nonwaterbirth. Mother–
newborn dyads who transferred to the hospital during the
postpartum period were retained in the sample because, if
in fact waterbirth itself introduces risk (eg, infection, respi-
ratory distress), we would expect to see more women and
newborns with immediate postpartum newborn or maternal
complications requiring transfer and possible hospitalization
following waterbirth. We also excluded 12 singleton pregnan-
cies for which the waterbirth variable was missing. Apply-
ing these inclusion criteria resulted in a sample size of 18,397
neonates (N = 18,343 pregnancies), as shown in Figure 1.

Variables

The main exposure, waterbirth, was collected as a 3-level cat-
egorical variable. To the question “Baby born underwater?”
the midwife had 3 answer options: “no”; “yes”; or “intended,
but not born underwater.” Throughout this article, we refer
to these categories as nonwaterbirth, waterbirth, and intended
waterbirth, respectively.

12 Volume 61, No. 1, January/February 2016

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n=24,848 pregnancies
(n=24,969 newborns; 119 sets
of twins and 1 set of triplets)

21,414 pregnancies
21,495 newborns (81 sets of twins)

18,363 pregnancies
18,417 newborns (54 sets of twins)

3433 (3473 newborns)
plus 1 record that had
missing data = 3 434

Stopped receiving care from this
midwife prior to the onset of labor

yes

Location of birth:
home or birth center yes

no 2949 (2976 newborns) hospital
100 ‘other’
2 missing

18,355 pregnancies
18,409 newborns (54 sets of twins)

Neonate born alive
yes

no 8 IUFDs (intrauterine fetal
demise) after the onset of
labor, but prior to birth

10,252 pregnancies
10,290 newborns (38 sets of twins)

6521 pregnancies
6534 newborns (13 sets of twins)

1570 pregnancies
1573 newborns (3 sets of twins)

non -waterbirth

waterbirth

intended waterbirth

12 singleton pregnancies
were missing data on
waterbirth

Figure 1. Sample Size Delimitation
Begins with all records entered into MANA Stats for birth years 2004 to 2009. Women who changed providers (ie, stopped receiving care from the
midwife filling out the data form) prior to the onset of labor are excluded. Some of these women may be included as separate records if they changed
providers to another MANA Stats contributor; however, many developed a complication requiring maternity specialty care and therefore would not
be included. Also excluded are women who did not give birth at home or at a birth center, and mother—fetus dyads if the fetus died prior to birth.
All numbers are counts of singleton pregnancies, unless otherwise indicated.

Abbreviation: MANA Stats, Midwives Alliance of North America Statistics.

Neonatal outcomes included a 5-minute Apgar score of
less than 7 (yes/no), postpartum transfer to the hospital for a
newborn indication (referred to hereafter as neonatal trans-
fer, yes/no), any infant admission to the hospital during the
first 6 weeks of life (yes/no), and any NICU admission during
the first 6 weeks of life (yes/no). Although we knew the num-
ber of events would be small based on our previous work with
this dataset,33 we also included early (prior to 7 completed
days of life) and late (at least 7 completed days of life, but not
yet 28) neonatal deaths as end points.

Maternal outcomes included postpartum reproductive
tract infection at any time during the first 6 weeks postpar-
tum (presence of: uterine infection, urinary tract infection, or
delayed perineal healing/infection), postpartum transfer for
a maternal indication (referred to hereafter as postpartum
transfer; yes/no), anymaternal admission to the hospital dur-
ing the first 6 weeks postpartum (yes/no), and genital tract
trauma. The degree of genital tract trauma was evaluated first
as a simple dichotomous variable and then further as a mul-
tilevel nominal variable with the following categories: none,
episiotomy only, first- or second-degree perineal only, third-

or fourth-degree perineal only, mild labial only, more severe
labial only (defined on the data collection formas required re-
pair), other trauma requiring repair, trauma at multiple sites,
and trauma not otherwise specified. The latter category con-
sisted of women for whom the midwife indicated that, yes,
there was trauma, but then did not answer the follow-up ques-
tions regarding location and severity.

For the neonatal and postpartum transfers,midwiveswere
able to indicate multiple indications for transfer. It is there-
fore possible that one mother–newborn dyad could have ex-
perienced both a postpartum transfer and a neonatal transfer
if, for example, the midwife indicated both “extensive lacera-
tion repair requiring anesthesia” and “evaluation of congenital
anomalies” as reasons for transfer.

Analysis

We used logistic regression to analyze all dichotomous out-
comes (5-minute Apgar score of � 7, neonatal transfer, NICU
admission, infant hospitalization in the first 6 weeks, post-
partum transfer, postpartum reproductive tract infection,

Journal of Midwifery &Women’s Health � www.jmwh.org 13

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maternal hospitalization in the first 6 weeks, dichotomized
trauma). Directed Acyclic Graph (DAG) methodology41,42
was used to determine potential confounders.Directed acyclic
graphs are a type of causal model that allow the researcher to
determine a complete set of potential confounders that maxi-
mizes use of available data while simultaneously reducing bias
that would result from adjusting for highly collinear covari-
ables. The DAG/causal model that we drew for this analysis is
available from the authors on request; as a result of the DAG
analysis, we controlled for primiparity in all models.

The 3-level waterbirth exposure variable was entered into
the models as a nominal variable, with nonwaterbirth as the
reference category. Our results are thus presented as adjusted
odds of a given outcome for waterbirth compared to nonwa-
terbirth and, separately, adjusted odds of a given outcome for
intended waterbirth compared to nonwaterbirth.

As expected, cell counts were very low for the neona-
tal death outcomes. Thus, for these outcomes we report the
raw data but did not calculate adjusted odds ratios and corre-
sponding 95% confidence limits.

For the multilevel nominal outcome (genital tract
trauma), we used multinomial (ie, not ordered) logistic
regression and controlled for primiparity. No trauma was the
reference category. Data were analyzed using SPSS 19.0.0.1
(IBM Corp, Armonk, NY) and S-Plus Version 8.1 (Tibco
Spotfire, Seattle, WA).

RESULTS

We report results from 18,343 births, which included 18,397
neonates (see Figure 1). Of these, 10,252 women (10,290
neonates) were in the nonwaterbirth group, 6521 women
(6534 neonates) were in the waterbirth group, and 1570
women (1573 neonates) were in the intended waterbirth
group. Demographics of the women in this sample are shown
in Table 1. Briefly, the majority were white, married, and col-
lege educated. The mean age at conception was 29.9 years
(standard deviation 5.3). Our sample does include larger
proportions of both Amish/Mennonite (6.0%) and grand-
multiparous women (8.5%), relative to the US population as
a whole; as expected, there is a large overlap between these 2
groups. Additionally of note, 968 women had vaginal births
after cesarean (VBACs), 134 gave birth to a neonate in breech
presentation, and 54 women had twins. Because our sample
was limited to those women who gave birth at home or in a
birth center, all of these were vaginal births.

Neonatal Outcomes

Neonates born underwater (waterbirths) fared better than
their nonwaterbirth counterparts on all neonatal outcome
measures, when controlling for primiparity (Table 2). The ad-
justed odds ratio (aOR) for neonatal transfer to the hospital,
for waterbirth neonates compared to nonwaterbirth neonates,
was 0.46 (95% confidence interval [CI], 0.32-0.68; P � .001).
The aOR for NICU admission during the first 6 weeks was
0.59 (95% CI, 0.46-0.76; P � .001); the aOR for any hospital
admission during the first 6 weeks was 0.75 (95% CI, 0.63-
0.88; P � .001) (Table 2). There was no evidence of 5-minute

Apgar scores below 7 being more common in the waterbirth
group (aOR, 0.88; 95% CI, 0.65-1.19; P = .42).

By contrast, neonates whose mothers intended a water-
birth but did not have one (intended waterbirths) fared worse
than neonates whosemothers had not planned to give birth in
the water. Neonates in the intended waterbirth category had a
102% increase in the odds of a 5-minute Apgar score of less
than 7 (aOR, 2.02; 95% CI,1.40-2.93; P � 0.001).

Although the number of events was too small for firm
conclusions, we found no evidence of increased neonatal
deaths (early or late) among neonates in the waterbirth group.
There were 9 deaths (6 early, 3 late) in the nonwaterbirth
comparison group; these were attributed to hypoxia, congen-
ital anomalies, chorioamnionitis, cord accidents (3), and un-
known causes (3). Among the waterbirth group, there were
3 neonatal deaths (2 early, one late), attributed to hypoxic
ischemic encephalopathy, congestive heart failure, and un-
known causes. In the intended waterbirth group, there were
also 3 neonatal deaths (2 early, one late), attributed to placen-
tal abruption, shoulder dystocia with compressed cord, and
hypoxia (Table 2).

Maternal Outcomes

Women who completed the second stage while immersed in
water (waterbirths) had a 35% reduction in odds of postpar-
tum transfer (aOR, 0.65; 95% CI, 0.50-0.84; P = .001) and a
28% reduction in odds of maternal hospitalization in the first
6 weeks (aOR, 0.72; 95% CI, 0.59-0.87; P � .001) (Table 3). By
contrast, women who had a waterbirth also had an 11% in-
crease in odds of experiencing any genital tract trauma (aOR,
1.11; 95% CI, 1.04-1.18; P = .002). When categories based
on trauma location and severity were assessed, however, there
was no discernible pattern between the women in the 3 co-
horts (Table 4). Women who planned a waterbirth but did not
have one (intended waterbirths) experienced substantially in-
creased odds of any genital tract trauma (aOR, 1.67; 95% CI,
1.49-1.87; P � .001) (Table 3).

DISCUSSION

Main Findings and Interpretation

This retrospective cohort study is the largest study on this
topic to date and one of the first to focus on a US population.
We found thatwaterbirthwas not associatedwith an increased
risk of 5-minute Apgar score of less than 7, immediate neona-
tal transfer of care to a hospital, any neonatal hospitalization
in the first 6 weeks, or NICU admission in the first 6 weeks.
For women, we found that waterbirth was associated with re-
duced risk of both immediate postpartum transfer of care to a
hospital and any maternal hospitalization in the first 6 weeks.
However, waterbirth was associated in our data with an in-
creased risk of genital tract trauma. We found no evidence of
an association between waterbirth and uterine, endometrial,
or perineal infection.

A recent Cochrane review on waterbirth stated that: “Im-
mersion during the 2nd stage of labour needs further investi-
gation, but at present there is no clear evidence to support or
not to support a woman’s decision to give birth in water.”18
This review, as is the case for all Cochrane Collaboration

14 Volume 61, No. 1, January/February 2016

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Table 1. Sample Demographics and Pregnancy Characteristics for 18,343Women (18,397 neonates) WhoGave Birth at Home or in a Birth
Center with a Midwifea

Total Sample Nonwaterbirth Waterbirth Intended

Waterbirth

N ()

n () n () n ()

Race/ethnicity (categories are not mutually exclusive)b

African or Caribbean 386 (2.1) 220 (2.1) 122 (1.9) 44 (2.8)

Asian 820 (4.5) 471 (4.6) 274 (4.2) 75 (4.8)

White 16,785 (91.8) 9336 (91.1) 6027 (92.5) 1422 (90.7)

Hispanic 786 (4.3) 448 (4.4) 262 (4.0) 76 (4.8)

Native American 192 (1.0) 117 (1.1) 64 (1.0) 11 (0.7)

Other 373 (2.0) 206 (2.0) 129 (2.0) 38 (2.4)

Special groups (categories are not mutually exclusive)

Amish/Mennonite/other Plain Church community 1081 (5.9) 963 (9.4) 121 (1.9) 23 (1.5)

Immigrant 504 (2.7) 298 (2.9) 156 (2.4) 50 (3.2)

Educationc

Less than high school 1338 (7.5) 1094 (10.9) 200 (3.1) 44 (2.9)

Completed high school 3126 (17.5) 1756 (17.5) 1134 (17.8) 236 (15.4)

Completed 1-3 years of college 4552 (25.4) 2425 (24.2) 1726 (27.1) 401 (26.2)

Completed at least 4 years of college 8885 (49.6) 4739 (47.3) 3297 (51.9) 849 (55.5)

Marital statusd

Married 16,139 (88.0) 9031 (88.1) 5750 (88.2) 1358 (86.5)

Partnered (although not married) 1717 (9.4) 950 (9.3) 589 (9.0) 178 (11.3)

Single (includes separated/divorced) 420 (2.3) 238 (2.3) 153 (2.4) 29 (1.9)

Pregnancy characteristics

Primiparouse 4001 (21.8) 2316 (22.5) 1246 (19.1) 439 (28.0)

Multiparousf 13,184 (71.8) 7121 (69.5) 4984 (76.4) 1079 (68.7)

Grand multiparousg 1158 (6.3) 815 (7.9) 291 (4.5) 52 (3.3)

History of cesareanh 967 (5.3) 535 (5.2) 327 (5.0) 105 (6.7)

Breech birthi (denominator is newborns) 134 (0.7) 85 (0.8) 29 (0.4) 20 (1.3)

Multiple birth 54 (0.3) 38 (0.4) 13 (0.2) 3 (0.2)

aData come from the Midwives Alliance of North America Statistics Project, birth years 2004 to 2009.
bFourteen women were missing data on race.
cThree hundred ninety-six women were missing data on education.
dEight women were missing data on partner status.
eOne woman was missing data on parity.
fIncludes women with 2-4 previous births only; primiparous, grand multiparous, and multiparous are mutually exclusive groups.
gGrand multiparous is defined as at least 5 previous births (live births or stillbirths after 20 weeks’ gestation).
hEight women were missing data on history of cesarean.
iSixty-one newborns were missing data on presentation.

publications, focused exclusively on results of randomized
controlled trials (RCTs), of which there are only a few compar-
ing waterbirth to nonwaterbirth43,44—and these were small
and underpowered. Another problem inherent in these stud-
ies, as well as in any large, future, hypothetical RCTs, is that
women in the waterbirth group whose labors become com-
plicated are often directed to discontinue immersion,45,46 but
women randomized to nonwaterbirth would not suddenly be
asked to get in the water. This one-way noncompliance with
the assigned intervention group could introduce differential
misclassification bias, making interpretation of intention-to-
treat results problematic. This bias is also apparent in obser-
vational studies: womenwho develop complications get out of
the tub, but rarely do womenwho never intended a waterbirth
suddenly decide to get in. To our knowledge, we are the first
to address this issue by reporting separately on the intended
waterbirth group.

These methodologic issues, taken together, led the
Cochrane review’s authors to state unprecedentedly (the
Cochrane Group is well known for their randomized trial
preference) that: “Large audits and cohort studies should be
undertaken in units which provide a pool facility to provide
evidence for practice.”18 In this article, we have presented re-
sults from just such a large cohort study: 18,397 neonates, 35%
(n= 6534) of whowere born underwater. Furthermore, this is
the first waterbirth study to report results for a US population.

We found that neonates born underwater were not at in-
creased risk of adverse outcomes; on the contrary, they fared
better than their nonwaterbirth counterparts on all outcomes.
Rather than being a true benefit of waterbirth, however, this
finding is likely secondary to the misclassification bias de-
scribed above: outcomes in the intended waterbirth group
were uniformly worse than those observed in the (planned)
nonwaterbirth group. Taken together, these findings suggest

Journal of Midwifery &Women’s Health � www.jmwh.org 15

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Table 2. Comparison of Newborn Outcomes in Newborns Born Underwater (Waterbirth), Newborns Not Born Underwater (Nonwaterbirth),
and NewbornsWhoseMothers Intended a Waterbirth But Did Not Have One (IntendedWaterbirth)a

Frequencies Adjusted Results

Nonwaterbirth Waterbirth

Intended

Waterbirth Waterbirth IntendedWaterbirth

n = , n =  n =  Nonwaterbirth aOR ( CI) P Value aOR ( CI) P Value
5-minute Apgar score<7,b n (%)

No 10,125 (98.8) 6451 (99.0) 1526 (97.6) –

Yes 120 (1.2) 66 (1.0) 38 (2.4) 1.0 0.88 (0.65, 1.19) .42 2.02 (1.40, 2.93) � .001

Transfer to the hospital during the postpartumperiod for a neonatal indication,c n (%)

No 10,094 (98.8) 6463 (99.5) 1532 (98.4) –

Yes 118 (1.2) 34 (0.5) 25 (1.6) 1.0 0.46 (0.32, 0.68) � .001 1.33 (0.86, 2.06) .20

Infant hospitalization, first 6 weeks,d n (%)

No 9809 (95.5) 6301 (96.6) 1484 (94.5) –

Yes 465 (4.5) 220 (3.4) 87 (5.5) 1.0 0.75 (0.63, 0.88) � .001 1.21 (0.95, 1.53) .12

NICU admission, first 6 weeks,e n (%)

No 10,013 (97.6) 6426 (98.6) 1521 (97.1) –

Yes 242 (2.4) 90 (1.4) 45 (2.9) 1.0 0.59 (0.46, 0.76) � .001 1.18 (0.85, 1.63) .32

n (rate/1000) n (rate/1000) N

(rate/1000)

Early neonatal death (7 completed days)f

No, n 10,280 6532 1569

Yes, n

(rate/1000)

6g (0.58/1000) 2h (0.31/1000) 2i (1.27/1000) k k k

Late neonatal death (at least 7, but not yet 28, completed days)m

No, n 10,276 6529 1568

Yes, n

(rate/1000)

3n (0.29/1000) 1p (0.15/1000) 1q (0.64/1000) k k k

Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; NICU, neonatal intensive care unit.
aRaw data as well as adjusted odds ratios (aOR) and 95% confidence intervals (95% CI) are presented; the nonwaterbirth group serves as the reference category. Analyses
adjust for primiparity.
bSeventy-one neonates were missing data on 5-minute Apgar score.
cAcross all 3 groups, the most common reasons for transfer were respiratory distress and/or low Apgar score. One hundred thirty-one neonates were missing data on neonatal
transfer.
dThirty-one neonates were missing data on hospitalizations in the first 6 weeks.
eSixty neonates were missing data on NICU admissions in the first 6 weeks.
fThere are no missing data for the death variables. The 4 nonwaterbirth and 2 intended waterbirth neonates not accounted for here died of autopsy-confirmed congenital
anomalies that are incompatible with life and were removed from analysis, as is customary when examining fetal/neonatal death as an outcome.
gCauses of death: 1) hypoxia (neonate never attempted to breathe; life support removed after 2 days; no autopsy); 2) patent ductus arteriosis was official cause but no autopsy;
3) prelabor brain damage (tight nuchal cord; neonate never attempted to breathe; life support removed after 2 days; no autopsy but brain damage was receiving obstetrician’s
diagnosis); 4) acute chorioamnionitis (autopsy-confirmed); 5) cord rupture/hemorrhage (autopsy-confirmed); and 6) unknown (no autopsy; official cause was cardiac
failure).
hCauses of death: 1) hypoxic ischemic encephalopathy (confirmed with magnetic resonance imaging on day 4; life support subsequently removed); and 2) congestive heart
failure (autopsy-confirmed).
iCauses of death: 1) placental abruption (placenta came out with neonate; no autopsy); and 2) shoulder dystocia with cord compression (autopsy-confirmed).
kCell counts too low to produce reliable effect estimates.
mThere are no missing data for the death variables. The one nonwaterbirth and 2 waterbirth neonates not accounted for here died of autopsy-confirmed congenital anomalies
that are incompatible with life and were removed from analysis, as is customary when examining fetal/neonatal death as an outcome. Also not included here are neonates who
died during the early neonatal period; the denominator for late neonatal death rates has been limited to those infants still at risk of the outcome.
nCauses of death: 1) cord prolapse (no autopsy); 2) unknown (neonate never attempted to breathe and did not respond to resuscitation; no autopsy; this woman had a
subsequent neonate with the same issue); and 3) unknown (no autopsy).
pCause of death: unknown (no autopsy).
qCause of death: official cause was hypoxia, but there was no autopsy.

that, when potential complications arose during labor, the at-
tending midwife recommended that the woman discontinue
water immersion, perhaps to allow for closer monitoring of
fetal heart tones or to visualize fetal scalp color, etc. Thus,
the intended waterbirth category reflects a cohort of women
who were experiencing more complicated labors or births. It
is not surprising that the outcomes forwomen and neonates in
the intended waterbirth category were worse. Following, it is
also not surprising that the neonates of women who remained
in the tub or pool (the waterbirth group) had better out-

comes: all of the nonstraightforward (ie, potentially elevated
risk) mother–newborn dyads had been asked to get out of the
tub. The substantially improved outcomes observed among
neonates who were born underwater is almost certainly an
artifact of this unavoidable but appropriate clinical manage-
ment. The nonwaterbirth comparison (reference) group con-
sists of women who never wanted (or who did not have access
to)waterbirth. It seems likely that some of thesewomenwould
have developed complications during labor that would have
led to discontinuing immersion, had they been laboring in

16 Volume 61, No. 1, January/February 2016

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Table 3. Maternal Outcomes ofWomenWhoHad a Waterbirth, Nonwaterbirth, or IntendedWaterbirth But Gave Birth Outside of the Planned
Water Immersiona

Frequencies Adjusted Results

Nonwaterbirth

n = ,

Waterbirth

n = 

Intended

Waterbirth

n =  Waterbirth IntendedWaterbirth

n () n () n () Nonwaterbirth aOR ( CI) P Value aOR ( CI) P Value
Maternal genital tract trauma (any)b

No 5162 (50.7) 3186 (49.3) 581 (37.4) –

Yes 5018 (49.3) 3272 (50.7) 973 (62.6) 1.0 1.11 (1.04-1.18) .002 1.67 (1.49-1.87) � .001

Postpartum transferc

No 9990 (98.0) 6415 (98.8) 1514 (97.2) –

Yes 199 (2.0) 80 (1.2) 43 (2.8) 1.0 0.65 (0.50, 0.84) .001 1.36 (0.97, 1.90) .07

Maternal hospitalization, first 6 weeksd

No 9890 (96.6) 6354 (97.6) 1502 (95.9) –

Yes 343 (3.4) 154 (2.4) 65 (4.1) 1.0 0.72 (0.59, 0.87) � .001 1.17 (0.89, 1.54) .21

Maternal postpartum reproductive tract infectione

No 10,002 (97.8) 6389 (98.2) 1525 (97.6) –

Yes 221 (2.2) 119 (1.8) 38 (2.4) 1.0 0.87 (0.69, 1.09) .23 1.08 (0.78, 1.52) .69

Abbreviations: aOR, adjusted odds ratios; CI, confidence interval.
aRaw data as well as aOR and 95% CIs (95% CI) are presented; all analyses adjust for primiparity.
bOne hundred fifty-one women were missing data on genital tract trauma.
cOne hundred and two women were missing data on postpartum transfer.
dThirty-five women were missing data on hospitalization in the first 6 weeks postpartum.
eForty-nine women were missing data on postpartum reproductive tract infection (includes endometrial, perineal, or uterine infection in the first 6 weeks postpartum).

water. Therefore, the nonwaterbirth reference group contains
bothwomenwho could have hadwaterbirths and thosewhose
labors were more complicated, and who therefore would have
been asked to get out of the tub; for women who plan water-
births, these 2 exposure groups have been separated into wa-
terbirth and intended waterbirth.

Nonetheless, the neonates in the waterbirth group were
born underwater, and we found no evidence of any sub-
sequent increased risk for any adverse neonatal outcome.
Safety of waterbirth (as opposed to merely laboring in wa-
ter) is currently the issue under heaviest scrutiny in the recent
ACOG/AAP guidelines,3 as well as the evidence gap identi-
fied by the authors of the Cochrane Review.18 Based on the
strength of evidence presented here, we cannot conclude that
waterbirth is beneficial; however, based on our results, wa-
terbirth certainly is not harmful to the neonate. Our findings
also suggest that US midwives attending home and birth cen-
ter births on the whole are appropriately managing women as
they labor and birth in water.

Our newborn morbidity results are consistent not

only

with those in the Cochrane review18 but also with those
of most other published observational studies, which al-
most universally report no adverse outcomes for waterbirth
neonates.26–35,46,47 By contrast, Carpenter et al48 reported an
increase in respiratory distress symptoms among waterbirth
neonates; however, the sample size was small (N = 38), and
the authors reflect that ascertainment bias may have played
a prominent role. Hawkins,49 in a small (N = 32), non-
randomized cohort study, reported more neonatal infections
(and therefore greater morbidity) in the waterbirth group, al-
though during the study period a lack of adherence to tub-

cleaning protocols required intervention by the hospital’s in-
fection control team, likely affecting the study’s results. All
other published reports of increased neonatal morbidity fol-
lowing waterbirth are case reports or case series without con-
trol groups.1,14,21–24,45,50–57

We lacked sufficient power to calculate reliable adjusted
odds ratios for early and late neonatal deaths. Nonetheless,
there was no evidence of elevated mortality among the wa-
terbirth group, a finding that is consistent with our morbidity
results as well as with those published by others.26,58 Further-
more, of the 3 neonatal deaths in the waterbirth group, none
were attributed to causes that might stem from the waterbirth
(ie, no drowning, no cord avulsion, no respiratory distress).

Women in our sample who gave birth while immersed in
water had no increased risk of adverse outcomes except for
genital tract trauma: they experienced an 11% increase in odds
of genital tract trauma, although without a discernible pattern
as to trauma location and severity. Cortes et al59 also reported
an increased risk of perineal trauma for women who gave
birth while immersed in water. The Cortes study, however,
contradicts the bulk of the literature, which has reported re-
duced risk of genital tract trauma, or no change in risk, among
women who had a waterbirth.26–28,32–34,44,46,47,60 Because ours
is the first large cohort study to report results in a US popu-
lation, and the largest cohort study to date, our finding of in-
creased risk of maternal genital tract trauma requires further
investigation. In the meantime, clinicians should discuss the
possible risk of genital tract trauma as part of shared decision
making and the informed consent process around waterbirth.

Other studies have also reported no increased risk
of infection among women who have waterbirths,26,29,32,61

Journal of Midwifery &Women’s Health � www.jmwh.org 17

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Table 4. Comparison of Location and Severity ofMaternal Birth Canal Trauma byWhether or Not the BirthWas a Waterbirth,
a Nonwaterbirth, or an IntendedWaterbirtha

Frequencies Adjusted Results

Nonwaterbirth

n = ,

Waterbirth

n = 

Intended

Waterbirth

n =  Waterbirth IntendedWaterbirth

n () n () n ()

Non-wat-

erbirth aOR ( CI) P Value aOR ( CI) P Value
None 5162 (50.6) 3186 (48.9) 581 (37.3) –

Episiotomy only 21 (0.2) 1 (0.02) 11 (0.7) b b b

1st- or 2nd-degree

perineal only

3,140 (30.8) 1980 (30.4) 547 (35.1) 1.0 1.06 (0.98, 1.14) .13 1.52 (1.34, 1.73) � .001

3rd- or 4th-degree

perineal only

63 (0.6) 27 (0.4) 13 (0.8) 1.0 0.79 (0.50, 1.24) .30 1.73 (0.94, 3.18) .07

Mild labial only 551 (5.4) 487 (7.5) 101 (6.5) 1.0 1.50 (1.32, 1.71) � .001 1.74 (1.39, 2.17) � .001

More severe: labial

only

142 (1.4) 87 (1.3) 27 (1.7) 1.0 1.10 (0.84, 1.45) .50 1.61 (1.06, 2.46) .028

Other trauma

requiring repair

21 (0.2) 6 (0.09) 2 (0.1) b b b

Trauma at multiple

sites

1080 (10.6) 684 (10.5) 263 (16.9) 1.0 1.10 (0.99, 1.23) .085 2.09 (1.77, 2.47) � .001

Trauma NOS 63 (0.6) 61 (0.9) 14 (0.9) 1.0 1.60 (1.12, 2.28) .01 1.96 (1.09, 3.52) .025

Abbreviations: aOR, adjusted odds ratio; CI, confident interval; NOS, not otherwise specified.
aRaw data as well as aOR and 95% CIs (95% CI) are presented. The multinomial logistic regression model controlled for primiparity.
bCell counts too low to produce reliable effect estimates.

although one study found an elevated risk.35 In our study, we
found no association between waterbirth and maternal per-
ineal, uterine, or endometrial infection.

Women in the intended waterbirth category had in-
creased odds of all adverse outcomes, although only genital
tract trauma was statistically significant. As discussed above,
this finding could be an artifact of the misclassification
bias wherein women experiencing complicated labors were
asked to discontinue water immersion. Alternatively, perhaps
midwives attempted to speed the second stage in cases of fetal
distress by cutting an episiotomy or allowing/encouraging
tearing by verbally coaching a woman to continue to push,
or push harder, in the final moments of birth. Alternatively,
some underlying condition or risk factor (eg, smoking or
poor nutrition) that predisposes to fetal complications could
also place the woman at risk for reduced tissue integrity.62

Strengths and Limitations

This research uses data from the MANA Stats Project, birth
years 2004 to 2009. Although this dataset has many strengths,
including evidence of reliability and validity, data collection
procedures that preclude a midwife from entering data only
from births with good outcomes, a large sample size, ex-
tremely high participation by women, and large numbers of
covariables,36 it does have limitations. Chief among these
is the fact that data are collected by a voluntary sample of
midwives. We previously estimated that approximately 30%
of midwives attending home or birth center births in the
United States contribute data,36 and it is certainly possible that
contributing midwives are not representative of all midwives

attending US home and birth center births.We cannot predict
how this would affect our results on waterbirth.

Additionally, our results are based on women who gave
birth at home or in a birth center. These women likely are not
representative of the US childbearing population as a whole.
Additionally, they by definition gave birth withminimalmed-
ical intervention, which also is not the norm for US women,
for whom the majority of births occur in the hospital under
biomedical management.63,64 However, because the few US
hospitals that do offer birth tubs typically prohibit their use by
higher risk women and by women who utilize epidural anal-
gesia or other ongoing interventions,28 and because even in
hospitals the vast majority of laboring women are low-risk at
the onset of labor, it seems reasonable that our results could
be applied in US hospital settings where waterbirth is offered.

CONCLUSION

This study is the largest cohort study to date on waterbirth,
the first large study from the United States, and the first to re-
port separately on outcomes for mother–newborn dyads who
did not complete a planned waterbirth because of risk factors
that arose in the intrapartum period. Our results indicate that
waterbirth does not confer an increased risk of morbidity or
mortality for the newborn, but women completing the second
stage immersed in water may experience more genital tract
trauma. Our results are congruent with findings from studies
in other settings, and contrary to the recently published
ACOG/AAP clinical guidelines, suggest that waterbirth is a
reasonably safe option for use in low-risk, low-intervention

18 Volume 61, No. 1, January/February 2016

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Highlight

births—especially when the risks associated with other forms
of pharmacologic pain management are considered.

AUTHORS

Marit L. Bovbjerg, PhD, MS, is Instructor in the Epidemiol-
ogy Program, College of Public Health and Human Sciences
at Oregon State University in Corvallis, Oregon. She is also
Director of Data Quality for the Midwives Alliance of North
America Division of Research.

Melissa Cheyney, PhD, CPM, LDM, is Associate Professor of
medical anthropology and reproductive biology in the De-
partment of Anthropology at Oregon State University in Cor-
vallis, Oregon. She is also a certified professional midwife,
licensed in the State of Oregon, and Chair of the Division of
Research for the Midwives Alliance of North America.

Courtney Everson,MA, PhD, is aMedical Anthropologist and
the Graduate Dean at the Midwives College of Utah in Salt
LakeCity, Utah. She is also theDirector of Research Education
for the MANA Division of Research.

CONFLICT OF INTEREST

The authors have no conflicts of interest to disclose.

ACKNOWLEDGMENTS

Wewould like to thank themany volunteers who have worked
to make the MANA Stats project a success, particularly Bruce
Ackerman, Wendy Gordon, Ellen Harris-Braun, Saraswathi
Vedam, and Trinlie Wood. We also acknowledge the hard
work of theMANADivision of Research Coordinating Coun-
cil, as well as that of the MANA Board of Directors, without
whose support this project would not be possible. Ongoing
data collection efforts for the MANA Stats Project are funded
by MANA and the Foundation for the Advancement of Mid-
wifery.

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20 Volume 61, No. 1, January/February 2016

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