Birth Outcomes of Women with Obesity Enrolled for Care at Freestanding Birth Centers in the United States

Abstract

Introduction
Current US guidelines for the care of women with obesity generalize obesity‐related risks to all women regardless of overall health status and assume that birth will occur in hospitals. Perinatal outcomes for women with obesity in US freestanding birth centers need documentation.

Methods
Pregnancies recorded in the American Association of Birth Centers Perinatal Data Registry were analyzed (n = 4,455) to form 2 groups of primiparous women (n = 964; 1:1 matching of women with normal body mass indices [BMIs] and women with obese BMIs [>30]), using propensity score matching to address the imbalance of potential confounders. Groups were compared on a range of outcomes. Differences between groups were evaluated using χ² test for categorical variables and Student's t test for continuous variables. Paired t test and McNemar's test evaluated the differences among the matched pairs.

Results
The majority of women with obese BMIs experienced uncomplicated perinatal courses and vaginal births. There were no significant differences in antenatal complications, proportion of prolonged pregnancy, prolonged first and second stage labor, rupture of membranes longer than 24 hours, postpartum hemorrhage, or newborn outcomes between women with obese BMIs and normal BMIs. Among all women with intrapartum referrals or transfers (25.3%), the primary indications were prolonged first stage or second stage (55.4%), inadequate pain relief (14.8%), client choice or psychological issue (7.0%), and meconium (5.3%). Primiparous women with obesity who started labor at a birth center had a 30.7% transfer rate and an 11.1% cesarean birth rate.

Discussion
Women with obese BMIs without medical comorbidity can receive safe and effective midwifery care at freestanding birth centers while anticipating a low risk for cesarean birth. The risks of potential, obesity‐related perinatal complications should be discussed with women when choosing place of birth; however, pregnancy complicated by obesity must be viewed holistically, not simply through the lens of obesity.

Full text

Journal of Midwifery & Women’s Health www.jmwh.org
Original Research
Birth Outcomes of Women with Obesity Enrolled for Care at
Freestanding Birth Centers in the United States
Cecilia M. Jevitt1, CNM, PhD, RM ,SusanStapleton
2, CNM, DNP, Yanhong Deng3,PhD,XuemeiSong
3,MS,
Kaicheng Wang3, MD, MPH, Diana R. Jolles4, CNM, PhD
Introduction: Current US guidelines for the care of women with obesity generalize obesity-related risks to all women regardless of overall
health status and assume that birth will occur in hospitals. Perinatal outcomes for women with obesity in US freestanding birth centers need
documentation.
Methods: Pregnancies recorded in the American Association of Birth Centers Perinatal Data Registry were analyzed (n =4,455) to form 2 groups
of primiparous women (n =964; 1:1 matching of women with normal body mass indices [BMIs] and women with obese BMIs [>30]), using
propensity score matching to address the imbalance of potential confounders.Groups were compared on a range ofoutcomes. Differences between
groups were evaluated using χ2test for categorical variables andStudent’s ttest for continuous variables. Paired ttest and McNemar’s test evaluated
the differences among the matched pairs.
Results: The majority of women with obese BMIs experienced uncomplicated perinatal courses and vaginal births. There were no significant
differences in antenatal complications, proportion of prolonged pregnancy, prolonged first and second stage labor, rupture of membranes longer
than 24 hours, postpartum hemorrhage, or newborn outcomes between women with obese BMIs and normal BMIs. Among all women with
intrapartum referrals or transfers (25.3%), the primary indications were prolonged first stage or second stage (55.4%), inadequate pain relief
(14.8%), client choice or psychological issue (7.0%), and meconium (5.3%). Primiparous women with obesity who started labor at a birth center
had a 30.7% transfer rate and an 11.1% cesarean birth rate.
Discussion: Women with obese BMIs without medical comorbidity can receive safe and effective midwifery care at freestanding birth centers
while anticipating a low risk for cesarean birth. The risks of potential, obesity-related perinatal complications should be discussed with women
when choosing place of birth; however, pregnancy complicated by obesity must be viewed holistically, not simply through the lens of obesity.
J Midwifery Womens Health 2021;66:14–23 c2020 The Authors. Journal of Midwifery & Women’s Health published by Wiley Periodicals LLC on
behalf of American College of Nurse Midwives (ACNM).
Keywords: obesity, overweight, freestanding birth centers, birth center, midwife, pregnancy, birth, perinatal obesity
INTRODUCTION
Freestanding birth centers following American Association of
Birth Centers (AABC) standards are designed for women an-
ticipating a healthy, low-risk pregnancy and birth.1Birth cen-
ters are founded in midwifery-led care that supports physio-
logic pregnancy, birth and newborn transition through health
education that promotes individual responsibility and self-
care, and screening that assumes pregnancy and birth are
normal until complications are evident.1The most important
concept in birth center organization is the separation of pri-
mary care from acute care, which requires hospitalization.1
1University of British Columbia, Vancouver, British Columbia,
Canada
2American Association of Birth Centers, Perkiomenville,
Pennsylvania
3Yale Center for Analytical Sciences, Yale School of Public
Health, New Haven, Connecticut
4American Association of Birth Centers, Perkiomenville,
Pennsylvania
Correspondence
Cecilia M. Jevitt
Email: cecilia.jevitt@gmail.com
ORCID
Cecilia M. Jevitt https://orcid.org/0000-0002-4574-5650
Birth center philosophy and that of the midwifery model of
care are closely intertwined.1
Obesity, currently conceptualized as white adipose tissue
disease, now affects 36% of reproductive-age women in the
United States.2–4 Womenwithobesepregravidbodymassin-
dices (BMIs) are at increased risk for multiple perinatal com-
plications including gestational diabetes, hypertensive disor-
ders of pregnancy, prolonged pregnancy, prolonged phases
of labor, postpartum hemorrhage, cesarean birth, infection,
and thrombotic events.5–7 Newborns of women with obesity
are at increased risk for macrosomia, shoulder dystocia, and
stillbirth.5-7 As research revealed the health risks associated
with obesity, perinatal guidelines for the management of obe-
sity in pregnancy were developed assuming that the risks war-
ranted planning for hospital births.
American College of Obstetricians and Gynecologists
(ACOG) guidelines for pregnancy complicated by obesity as-
sume that births will occur in hospitals and that women with
obesity will have intravenous access and continuous elec-
tronic fetal monitoring.7Guidelines from the Royal College
of Obstetricians and Gynecologists advise that class I and
class II obesity (BMIs 30-39.9) in themselves are not rea-
sonsforwomentolaborandbirthinconsultant-ledunits
(physician-led hospital units) and that multiparous women
who are also healthy can plan for birth in midwifery-led units
14 1526-9523/09/$36.00 doi:10.1111/jmwh.13194
c2020 The Authors. Journa l of Midwifery & Women’s Health published by Wiley Periodicals LLC on behalf of American College of Nurse Midwives (ACNM)
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,provided the original
work is properly cited.

✦The majority of women with obese body mass indices (BMIs) in this study of freestanding birth centers experienced un-
complicated perinatal courses and gave birth vaginally.
✦There were no significant differences in the antenatal complications, proportion of prolonged pregnancy, prolonged first
and second stage labor, rupture of membranes longer than 24 hours, postpartum complications including postpartum
hemorrhage, or newborn outcomes between women with obese BMIs and normal BMIs.
✦Primiparous women with obesity who started labor at a birth center had a 30.7% hospital transfer rate and an 89% vaginal
birth rate.
✦The risks of potential, obesity-related perinatal complications should be discussed with women when choosing place of
birth; however, pregnancy complicated by obesity must be viewed holistically, not simply through the lens of obesity.
as long as clear referral paths are in place.8National Institute
for Health and Care Excellence guidelines from the United
Kingdom identify obesity with BMI greater than 35 as the
cutoff for indicating increased risk, therefore suggesting that
pregnant woman with a BMI greater than 35 require continu-
ous electronic fetal monitoring.9,10 No guidelines outline care
for women with obesity related to freestanding births centers
in the United States; however, women with obesity and BMIs
exceeding 40 receive care and give birth in AABC facilities, as
evidenced by their inclusion in the data set used in this study.
The perinatal outcomes of women with obesity receiving
antenatal care from physicians and giving birth in hospitals
have been documented and analyzed for 30 years.5–8 Multiple
studies have reported excellent perinatal outcomes for women
receiving antenatal care and giving birth in freestanding birth
centers;11–15 however, the outcomes specific to women with
obesity receiving care based on midwifery models and giving
birth in US freestanding birth centers have not been separately
examined. In this study, we compared maternal and neona-
tal outcomes between woman with normal weights and those
with obesity admitted to US birth centers.
The goals of this study were (1) to document the preg-
nancy and birth outcomes of women enrolled for birth cen-
ter care whose pregravid BMIs were 30 or greater compared
withwomenenrolledforbirthcentercareofnormalBMIsand
(2) to use the antepartum and intrapartum outcomes data of
women with obesity to form recommendations for the care of
obese women in freestanding birth centers while supporting
the best perinatal outcomes.
METHODS
Study Design
Data were obtained from AABC Perinatal Data Registry.6The
registry is used by 59% of AABC member birth centers and
27% of all US birth centers known to AABC and includes
comprehensivelydocumentedantenatalcare,labor,birth,and
newborn outcomes.13 All data from patients entering antena-
tal care at the birth center, regardless of planned birth loca-
tion, are entered into the online repository by the primary
provider or designee prospectively during the pregnancy at
4 points: initial antenatal visit; upon leaving antenatal care,
either admission in labor or transfer to other provider; after
birth; and at final postpartum visit. Birth centers contributing
data to the Perinatal Data Registry have individual and group
training workshops hosted by the AABC, use a standardized
instruction manual and data dictionary with definitions of all
variables, and receive periodic newsletters and e-mails from
the AABC to maintain data quality.
For this study, we extracted data from 2012 to 2015 con-
taining the perinatal records of more than 40,000 pregnan-
cies from 95 US birth centers. Data from planned hospital
births documented in the Perinatal Data Registry were ex-
cluded. BMI data were documented in 29,076 pregnancies.
Using World Health Organization definitions, BMI was cal-
culatedasweightinkilogramsdividedbytheheight(inme-
ters squared), and normal weight was defined as a BMI of 18.5
to 24.9, overweight as a BMI of 25 to 29.9, and obesity as a
BMI of 30 or greater.4Prepregnancy BMIs were used in this
analysis and were collected by the data registry platform based
upon either patient-reported prepregnancy weight or weight
at the first antenatal visit if occurring in the first trimester of
pregnancy. Use of prepregnancy BMI in the study is consis-
tent with the National Vital Statistic System, previous litera-
tures and guidelines for the care of women with obesity.16 Only
primiparous women were considered in this analysis because
BMI most often increases with pregnancy and the greatest risk
of complications occurs with the first pregnancy and birth.17,18
Multiparouswomenwerealsoexcluded,asstagesoflabortend
to be shorter after the first birth, confounding comparisons of
length of labor.
Matching comparable baseline characteristics (Table 2)
for the total subsample of women with obese BMIs using
propensity score matching yielded 2 matched groups (1:1,
n=964). The final sample was small because the number of
womenwithobesitywassmall.Allwomeninthepropensity
match planned to give birth in a birth center.
Outcome Variables
A range of prespecified maternal and neonatal outcomes was
considered, including antenatal, intrapartum, and postpar-
tum complications, intrapartum and postpartum maternal or
neonatal transfers, and referrals to hospital as defined in the
AABC Perinatal Data Registry. The definitions of many vari-
ableshavechangedovertimeoraredefineddifferentlyoutside
of the United States; for example, postpartum hemorrhage.13
Definitionsasusedinthisstudycanbefoundin
Journal of Midwifery & Women’s Health rwww.jmwh.org 15

Supporting Information: Appendix S1. These AABC registry
definitions are harmonized with ACOG Revitalize Data
definitions as well as the National Quality Forum Endorsed
measures. Newborn complications viewed as sentinel events
by AABC standards and the primary indications for newborn
transfer to hospital as defined in the AABC Perinatal Data
Registry included Apgar scores less than 7 at 5 minutes,
significant respiratory issues, temperature instability, tran-
sient tachypnea, hypoglycemia, birth trauma, congenital
anomalies, low birth weight, and prematurity.19
Statistical Analysis
Propensity score matching, the analysis method chosen for
this study, created 2 sets of participants, one exposure group
(women with obese BMIs) and a nonexposed, control group
(women with normal BMIs). By matching covariate charac-
teristics, the statistical procedure attempted to approximate a
random experiment and to reduce or eliminate selection bias.
Primiparous women with normal BMIs and primiparous
women with obese BMIs were matched with propensity
scores to address the imbalance of potential confounders.
The propensity score was estimated as the predicted probabil-
ity of a woman being in the obese BMI group from a logistic
regression model. The propensity-score model included
the categorical variables of race, insurance type, marital
status, smoking status and other medical conditions, and the
continuous variables age and years of education (Table 1).
Exclusions were those listed in the AABC Perinatal Data
Registry as physical and obstetric conditions that require
medical referral, including anorexia or bulimia, cervical ab-
normality, chronic hypertension, the woman herself being
born preterm, type 1 and type 2 diabetes, heart disease class
II-IV, HIV positive, infertility treatment resulting in current
pregnancy, seizures requiring treatment, sexually transmit-
ted infection in the 6 months prior to the current pregnancy,
thrombophilia, and uterine abnormality. Other medical con-
ditions included asthma and thyroid disease needing treat-
ment and nonchronic conditions not associated with obesity
such as vaginitis.
Matched pairs were formed between women in the nor-
mal BMI and obese BMI groups using a one-to-one opti-
mal fixed ratio matching with caliper width of 0·1. A total of
964 women were matched with a standardized mean differ-
ence of 0.0003 in propensity score. Only women matched with
propensity scores were included in the final analyses.
Categorical variables are displayed using frequency and
percentage, whereas continuous variables are displayed us-
ing means (SD) or medians (range). Differences between pre-
matched groups were evaluated using χ2test for categorical
variables and Student’s ttest for continuous variables. Mean-
while, paired ttest and McNemar’s test were performed to
evaluate the differences in the matched groups in considera-
tion of the correlation among the matched pairs. Standardized
differences were also provided to evaluate the differences on
baseline characteristics between 2 matched groups. All miss-
ing values were coded as not available and excluded from test.
APvalue of less than .05 was considered statistically signifi-
cant. All statistical analyses were conducted with SAS version
9.4 (SAS Institute, Cary, NC).
Human Subjects Protection
Written consent was obtained from all participants prior to
data entry into the registry. The data set obtained contained
no personal identifiers. The AABC Research Committee and
BoardofDirectorsapprovedthisstudyin2014andtheYale
UniversityHumanSubjectsCommitteegrantedanexemption
for analysis of deidentified data. All data were kept in Yale en-
crypted computers within Yale internet firewalls, which use
double password protection.
RESULTS
Population Characteristics
There were 8032 primiparous women who were 18 years older
at admission to the birth center. In the end, 4455 women were
left after exclusion using the criteria in Figure 1. Table 1 shows
demographic and health-related characteristics of women in
the initial sample (n =4455) and then in the propensity score-
matched sample (n =964).Intheinitialsample,womenwith
obeseBMIscomparedwithwomenwithnormalBMIswere
more likely to be identified as African American or other
race (P<.001), single (P=.002), covered by public insur-
ance (P<.001), and with history of smoking (P<.001).
Moreover, women with obese BMIs were significantly more
likely to have health-related concerns prior to antenatal care
enrollment than women with normal BMIs (18.3% vs 10.9%,
P<.001). Specifically, health-related concerns included
asthma, periodontal disease, thyroid disease, urinary tract
infection, and mental health concerns. After matching with
propensity score, no significant differences were observed
between women with normal BMIs and women with obese
BMIs. The standardized difference showed that 2 groups were
well-matched and the differences were minimal (range from
.005 to <.0001, Table 2).
Clinical Outcomes
The majority of women with obese BMIs in this study ex-
perienced uncomplicated antenatal and postpartum courses
and gave birth vaginally (Table 2). The primiparous women
with obese BMIs had vaginal birth rates slightly lower than
those of women with normal BMIs (87.5% and 91.7%, P=
.02). There were no significant differences in the antenatal and
intrapartum complications between women with obese BMIs
andnormalBMIs(Table2).
No significant differences were found in the proportions
of prolonged pregnancy, prolonged first and second stage la-
bor, rupture of membranes longer than 24 hours, or other
intrapartum complications (Table 2). Prolonged first stage
was the most common intrapartum complication, yet only
15.6% of all women had prolonged first stages (Table 3). Pro-
longed second stage was less common occurring in 6.5% of
labors. The second most common complication was nonpar-
ticulate meconium (7.9%, Table 3). Hypertensive disorders oc-
curred in 1% or less of women in both groups (Table 3). Of
women accepting prophylactic antibiotics, women with obe-
sity had higher rates of group B streptococcus (GBS) col-
onization (17.6% and 11.6%, P=.052, Table 2). There was
no difference in the proportion of women with obese BMIs
16 Volume 66, No. 1, January/February 2021

Ta b l e 1 . Comparison of Demographic Characteristics Before and After Propensity Score Matching
Original Groups Before Propensity Match Groups After Propensity Score Matching
Body Mass Index Category Body Mass Index Category
Characteristics Total Normal Obese PValueaTota l N o r m a l Obes e Std D i  PValueb
Total, n (% ) 4455 (100) 3973 (89.2) 482 (10.8) 964 (100) 482 (50) 482 (50) .0003
Body mass index, median (range) 22.1 (18.5-46.9) 21.9 (18.5-25) 32.8 (30.0-46.9) 27.5 (18.6-46.9) 22.1 (18.6-25.0) 32.8 (30.0-46.9)
Age, mean (SD), y 28.3 (4.6) 28.4 (4.5) 27.9 (4.8) .048 28.1 (4.8) 28.2 (4.8) 27.9 (4.8) .049 .92
Race, n (%) <.001 <.0001 .98
White 3732 (83.8) 3361 (84.6) 371 (77.0) 743 (77.1) 372 (77.2) 371 (77)
African American 171 (3.8) 130 (3.3) 41 (8.5) 83 (8.6) 42 (8.7) 41 (8.5)
Other 552 (12.4) 482 (12.1) 70 (14.5) 138 (14.3) 68 (14.1) 70 (14.5)
Ye a r s of e d u c a t i o n , me d i a n
(range)
16 (0-27) 16 (0-27) 15.5 (0-26) .003 16 (0-26) 16 (0-20) 15.5 (0-26) .018 .68
Insurance, n (%) <.001 .030 .77
Private insurance 2866 (64.3) 2580 (64.9) 286 (59.3) 574 (59.5) 288 (59.8) 286 (59.3)
Public insurance 849 (19.1) 717 (18) 132 (27.4) 260 (27) 128 (26.6) 132 (27.4)
Other 740 (16.6) 676 (17) 64 (13.3) 130 (13.5) 66 (13.7) 64 (13.3)
Marital status, n (%) .002 .014 .76
Single 944 (21.2) 816 (20.5) 128 (26.6) 253 (26.2) 125 (25.9) 128 (26.6)
Married 3511 (78.8) 3157 (79.5) 354 (73.4) 711 (73.8) 357 (74.1) 354 (73.4)
History of smoking, n (%) 173 (3.9) 140 (3.5) 33 (6.8) <.001 65 (6.7) 32 (6.6) 33 (6.8) <.0001 .84
Any medical history,cn(%) 523 (11.7) 435 (10.9) 88 (18.3) <.001 177 (18.4) 89 (18.5) 88 (18.3) .005 .88
Abbreviation: Std diff, standard difference.
aχ2test or Student’s ttest
bPaired ttest or McNemar’s test
cAny medical histor y is defined in the American Association of Birth Centers Perinatal Data Registry as any histor y of anorexia or bulimia, asthma (requiring prescription medication or in-patient treatment), bicornuate or septate uterus, chronic
hypertension (requiring prescription medication or in-patient treatment), chronic renal disease, client herself was born preterm (<37 weeks), depression or psychiatric illness (requiring prescription medication or in-patient treatment), diabetes
(preexisting), intimate partner violence, heart disease (class II-IV), HIV antibody positive, periodontal disease (bleeding or receding gums, caries, lack of dental care, poor dental hygiene), seizures (requiring prescription medication or in-patient
treatment), sexual abuse or assault history, substance abuse, thrombophilia, or thyroid dis ease (requiring prescription medication or in-patienttreatment).
Journal of Midwifery & Women’s Health rwww.jmwh.org 17

Figure 1. Sample Selection from American Association of Birth Centers Perinatal Data Registry
Abbreviation:BMI,bodymassindex.
aAmerican Association of Birth Centers Perinatal Data Registry.
bWorld Health Organization BMI categories were used: underweight, <18.5; normal weight, 18.5 to 24.9; overweight, 25 to 25.9; obese ≥30.
andthosewithnormalBMIswhotestedpositiveforGBSbut
did not receive prophylaxis before the birth (3.9% and 3.5%,
P=.3).
Overall intrapartum transfer rates were higher among
women with obese BMIs than woman normal BMIs (30.7%
vs 19.9%, P<.0001, Table 2). Prolonged first stage and in-
adequate pain relief were the 2 most common indications for
transfers that were recorded as referrals or emergency intra-
partum transfers to hospitals (Table 4). Other indications for
transfersarelistedinTable4butoccurredtooinfrequentlyfor
significance testing. No woman from either group had very
preterm labor, placenta previa, uterine hyperstimulation, se-
vere preeclampsia, eclampsia, seizures (noneclamptic), or sur-
gical injury during a cesarean birth. There were no maternal
intensive care unit admissions and no maternal or neonatal
deaths.
The proportion of postpartum complications, including
postpartum hemorrhage (6.4%, 4.8%) and retained placenta
(1.2%, 1.7%), were similar in women with normal and obese
BMIs (Table 2). The primary reasons for maternal postpartum
transfer included laceration or episiotomy requiring repair,
hypertension without evidence of preeclampsia, maternal
fever, preeclampsia, postpartum hemorrhage, and retained
placenta. Overall, there were no significant differences in
postpartum transfer or newborn transfer to a hospital for
extended care between the 2 groups. The average newborn
weights (3455 vs 3506 g) and Apgar scores were similar
between the 2 groups.
DISCUSSION
Obesity in the United States is associated with poverty in
a complex relationship that includes increased exposure to
endocrine-disrupting chemicals; limited ability to buy expen-
sive nutritious foods; residence in neighborhoods without full
service groceries; limited access to health care, fitness cen-
ters, or weight management programs; and neighborhoods
that are unsafe for outdoor physical activity.20,21 Consistent
with US national data, in the overall data set from the AABC
Perinatal Data Registry, Black or African American women
had higher rates of obesity.20,21 Although income data were
not included in this study, public insurance in the United
States is an indicator of low-income status. More women with
obese BMIs in the overall data set had antenatal coverage
through public programs than women with normal BMIs. In
this study, women with obese BMIs had higher indicators for
socioeconomic risk yet had outcomes similar to women with
normal BMIs.
Antenatal complications for women with obesity, includ-
ing minor complications such as anemia, were low, with 77.8%
having uncomplicated antenatal courses. A study of women
with BMIs greater than or equal to 30 in the United Kingdom
found similarly that 68% had no antenatal complications.22
Other studies of women with obesity receiving midwifery care
focus on intrapartum and postpartum outcomes.
Women with obesity in this study had significantly higher
rates of antenatal GBS colonization than women with normal
BMIs (17.6%, 11.6%). The American College of Obstetricians
18 Volume 66, No. 1, January/February 2021

Ta b l e 2 . Antepartum, Intrapartum, Postpartum, and Newborn Outcomes
Body Mass Index Category
Total N o r m a l Obes e PValue
a
Characteristics n = n = n =
Antenatal complications, n (%) .39
None 750 (77.8) 382 (79.2) 368 (76.3)
Any 214 (22.2) 100 (20.7) 114 (23.7)
Intrapartum complications, n (%) .53
None 505 (52.4) 273 (56.7) 232 (48.1)
1 298 (30.9) 140 (29.0) 158 (32.8)
2+161 (16.7) 69 (14.3) 92 (19.1)
Late term pregnancy 102 (10.6) 48 (10.0) 54 (11.2) .85
Intrapartum group B streptococcus colonization 141 (14.6) 56 (11.6) 85 (17.6) .004
Prolonged first stage labor 150 (15.6) 65 (13.5) 85 (17.6) .35
Prolonged second stage labor 63 (6.5) 34 (7.1) 29 (6.0) .22
Intrapartum, rupture of membranes >24 hr 54 (5.6) 22 (4.6) 32 (6.6) .16
Intrapartum transfer or referral, n (%) .88
No 720 (74.7) 386 (80.1) 334 (69.3)
Yes 244 (25.3) 96 (19.9) 148 (30.3)
Intrapartum transfer to hospital, prolonged or arrest first- or
second-stage labor
135 (14.0) 52 (10.8) 83 (17.2) .035
Birthtype(initialadmissionforlaboratbirthcenter),n(%) .47
Cephalic spontaneous vaginal 859 (89.6) 440 (91.7) 419 (87.5)
Primary cesarean birth 81 (8.4) 28 (5.8) 53 (11.1)
Instrumental (vacuum, forceps) 19 (2.0) 12 (2.5) 7 (1.5)
Postpartum c omplications, n (%) .31
None 869 (90.2) 431 (89.4) 438 (90.0)
Any 95 (9.9) 51 (10.6) 44 (9.1)
Postpartum hemorrhage 54 (5.6) 31 (6.4) 23 (4.8) .17
Postpartum retained placenta 14 (1.5) 6 (1.2) 8 (1.7) .27
Postpartum transfer or referral, n (%) .69
No 938 (97.3) 470 (97.5) 468 (97.1)
Yes 26 (2.7) 12 (2.5) 14 (2.9)
Newborn weight, mean (SD), g 3482 (419) 3455 (400) 3508 (436) .94
Apgarscoremin,n(%) .58
Normal (7-10) 890 (92.4) 440 (91.3) 450 (93.4)
Distressed 74 (7.7) 42 (8.7) 32 (6.6)
Apgar score  min, n (%) .34
Normal (7-10) 953 (98.9) 477 (99.0) 476 (98.8)
Distressed 11 (1.1) 5 (1.0) 6 (1.2)
Newborn transfer or referral, n (%) .11
No 945 (98.0) 473 (98.1) 472 (97.9)
Yes 19 (2.0) 9 (1.9) 10 (2.1)
aPaired ttest or McNemar’s test. Cases with missing data were excluded.
Journal of Midwifery & Women’s Health rwww.jmwh.org 19

Ta b l e 3 . Intrapartum Complications
Body Mass Index Category
Total No r m a l Obe s e PVa l u e b
Complicationan=n (%) n =n (%) n =n (%)
Prolonged first stage 150 (15.6) 65 (13.5) 85 (17.6) 0.51
Nonparticulate meconium 76 (7.9) 31 (6.4) 45 (9.3) 0.11
Prolonged second stage 63 (6.5) 34 (7.1) 29 (6.0) 0.74
Rupture of membranes >24 hr 54 (5.6) 22 (4.6) 32 (6.6) 0.43
Indeterminate fetal heart rate pattern 50 (5.2) 24 (5.0) 26 (5.4) 0.45
Particulate meconium 38 (3.9) 19 (3.9) 19 (3.9) 1
Shoulder dystocia requiring maneuvers 24 (2.5) 12 (2.5) 12 (2.5) 0.79
Malpresentation 16 (1.7) 8 (1.7) 8 (1.7) 0.71
Gestational hypertension 11 (1.4) 5 (1.0) 6 (1.2) 0.65
Chorioamnionitis 11 (1.1) 7 (1.5) 4 (0.8) 0.096
Abnormal FHR pattern 10 (1.0) 5 (1.0) 5 (1.0) 0.48
Maternal fever 8 (0.8) 3 (0.6) 5 (1.0) 1
Placental abruption 4 (0.4) 3 (0.6) 1 (0.2) 0.15
Preeclampsia 4 (0.4) 2 (0.4) 2 (0.4) 1
Preterm labor (labor 32 to 37 wk) 4 (0.4) 1 (0.2) 3 (0.6) 0.08
Stage 3 cord avulsion 1 (0.1) 1 (0.2) 0 N/A
Cord prolapse 1 (0.1) 1 (0.2) 0 N/A
Hemolysis, elevated liver enzymes, low platelets
syndrome
1 (0.1) 1 (0.2) 0 N/A
Other (any complication not listed above) 6 (0.6) 1 (0.2) 5 (1.0) N/A
Abbreviations: FHR, fetal heart rate; N/A, not applicable.
aAccording to American Association of Birth Centers standards these conditions make bir th center inappropriate and prompt hospital transfer.
bMcNemar’s test.
and Gynecologists describes US rates of GBS colonization
ranging from 10% to 30% varying with race and geographical
location.23 Several studies have shown that obesity is an inde-
pendent risk factor for colonization with GBS,23–25 with the
incidence of colonization increasing significantly with each
BMI unit.24 Colonization with GBS does not require hospital-
ization for births because intravenous antibiotic prophylaxis
is available to women in freestanding birth centers.
Reduction of cesarean births is a national quality strategy.
Women with obese BMIs receiving care based on generalized
medical guidelines may be at higher risk of cesarean birth and
related sequela.26,27 In this study, the birth center model of
care demonstrated a markedly lower cesarean birth rate for
women with obesity compared to the medical literature and
the US national cesarean rate. Women of mixed parity and
BMIs admitted to birth centers in labor in one US birth cen-
ter study had a 6% primary cesarean birth rate.15 In this cur-
rent study, the cesarean birth rate for women with obese BMIs
is significantly higher than women with normal BMIs (11.1%
vs 5.8%, P=.02), yet these rates that are dramatically lower
than the overall US low-risk cesarean birth rate of 26.9% for
primiparous women during the time of this study in 2013.28
Low risk was defined as singleton, greater than or equal to 37
weeks’ gestational age, and vertex in the 2013 analysis.28
Based on prior research, the cesarean birth rate for
primiparous women with obesity would be expected to be
higher.7,26,28 Inastudyof2235womenthatcalculatedcesarean
rate by BMI, rates were 31.4% for women of normal BMIs and
40.8% for women withobese BMIs.26 Another study including
143,403 women found that primiparous women with normal
BMIshada33.2%cesareanrateandwomenwithobeseBMIs
had an overall rate of 47.56%.27 These 2 studies represented
women cared for in obstetric units. In contrast, women with
obese BMIs in the UK Birthplace Study had a 13.6% cesarean
birth rate,12 and women with BMIs of at least 35 admitted to
alongside birth centers in England had a 4.7% cesarean birth
rate.29 Lower cesarean birth rates in these studies may be at-
tributable to evidence-based midwifery techniques including
delaying admission until labor is active, using upright posi-
tions and mobility during the first stage of labor, using relax-
ation techniques for labor pain relief, continuous support in
labor, and using water immersion during labor.27–31
Women with obese BMIs have been shown to have pro-
longed pregnancies, longer labors, increased use of oxytocin
during labor, increased use of oxytocin doses greater than
20 mU per minute, longer oxytocin use, and increased rates
of postpartum hemorrhage.32–35 Altered maternal and pla-
cental hormones, particularly leptin, are implicated in the
20 Volume 66, No. 1, January/February 2021

Ta b l e 4 . Primary Indication for Emergency Intrapartum Transfer or Referral
Body Mass Index Category
Total No r m a l Obe s e
Indications (n =)n (%) n (%) (.) n (%) (.)
Prolonged or arrest: first stage 118 (48.4) 43 (44.8) 75 (50.7)
Inadequate pain relief 36 (14.8) 13 (13.5) 23 (15.5)
Prolonged or arrest: second stage 17 (7.0) 9 (9.4) 8 (5.4)
Client choice/psychological 17 (7.0) 6 (6.3) 11 (7.4)
Prolonged ROM with labor >24 hr 11 (4.5) 4 (4.2) 7 (4.7)
Gestational hypertension 11 (4.5) 4 (4.2) 7 (4.7)
Particulate meconium 11 (4.5) 4 (4.2) 7 (4.7)
Indeterminate or concerning FHR pattern 10 (4.1) 6 (6.3) 4 (2.7)
Abnormal FHR pattern 5 (2.0) 2 (2.1) 3 (2.0)
Malpresentation 3 (1.2) 2 (2.1) 1 (0.7)
Nonparticulate meconium 2 (0.8) 1 (1.0) 1 (0.7)
Prolonged latent phase 2 (0.8) 1 (1.0) 1 (0.7)
Intrapartum hemorrhage 1 (0.4) 1 (1.0) 0
Abbreviations: FHR, fetal heart rate; ROM, rupture of membranes.
reduced cervical ripening and inhibited myometrial contrac-
tility in women with obesity.32–36 The women with obese BMIs
in this propensity match did notdiffer from women with nor-
mal BMIs in regard to postterm pregnancies (42 weeks or
greater)19 or length of stage 1 or stage 2 labor.
As in prior US birth center studies, the most common
postpartum complications were hemorrhage and retained
placenta.13,15 Prior birth center studies did not quantify post-
partum hemorrhage rates.13,15 In this study, rates for women
with obese BMIs were similar to those of women with normal
BMIs (4.8%, 6.4%). Primiparous women with obese BMIs re-
ceiving midwifery care at the University of Colorado Hospital
hada16.9%postpartumhemorrhagerateusingthesamedef-
inition as this study.27 Comparison with postpartum hemor-
rhage rates in recent US obstetrical literature and midwifery-
led, British alongside units cannot be done, as these studies
define postpartum hemorrhage as blood loss exceeding 1000
or 1500 mL following a vaginal birth. The fact that this study
used a lower definition of postpartum hemorrhage (500 mL)
and had only a 4.8% rate may indicate the overall health of the
women with obesity or more active management of the third
stage of labor.
Risk-based care for obesity in the United States is general-
ized to all women with obese BMIs regardless of obesity class
or comorbid conditions. This general application of guidelines
overmedicalizes care. Guidelines for obesity that are not data
based limit access to midwifery care for women with obesity
from vulnerable circumstances, care that has been shown safe,
effective, and cost-effective.11–15 Additionally, overapplication
of treatments meant to avoid obesity-related risk may un-
necessarily increase risk for iatrogenic complications such as
uterine hyperstimulation during augmentation of labor with
oxytocin.
With the safety of birth center care and midwifery
care for women with obese BMIs demonstrated in this and
other studies,12,29,30,32 attention must turn to the potential
individual and health systems savings that could be realized
if more women with obesity chose birth center care. Birth
center care reduces costs not only through reducing adverse
outcomesbutbyreducedlengthofstayandlowersupplyuse.
The US federal Strong Start for Mothers and Newborns initia-
tive analyzed outcomes from alternative maternity care mod-
els including freestanding birth centers, finding that women
who received prenatal care in birth centers had lower rates of
preterm and low birth weight newborns and lower rates of ce-
sarean births.37 Total average expenditures for women receiv-
ing care in the Strong Start group were $2010 lower than costs
for women in comparison groups.37 With more than one-third
of reproductive-aged women having obese BMIs, a shift to
greater use of birth centers could produce substantial savings.
Strengths and Limitations
This novel study provides insight from midwifery about
women with obesity receiving care and giving birth at free-
standing birth centers in the United States. The demographic
characteristics of women in this study mirror findings in US
obesity research, increasing generalizability.3,20 To inc r e a s e
comparability with most perinatal obesity research that used
prepregnancy BMI to calculate obesity-associated risk, only
prepregnancy BMI was used to define the groups in this study.
It is unknown how the cases where BMI were not recorded
comparewiththosewhereBMIwasrecorded.Thecompara-
bility of birth centers that contributed data to those that did
notisunknown.Excessgestationalweightgainwasnotcon-
sideredalthoughthisisknowntoincreasematernalandfetal
risk for adverse perinatal outcomes.7Additionally, generaliz-
ability of these outcomes is limited to women receiving care
in the midwifery and birth center models. Further research is
needed on the pregnancy and birth outcomes of women with
obese BMIs receiving midwifery care in general populations.
Journal of Midwifery & Women’s Health rwww.jmwh.org 21

CONCLUSION
This study adds evidence on the safety and benefits of
midwifery-provided antenatal care at freestanding births
centersforwomenwithobeseBMIs,aswellasintrapartum
and postpartum and birth care for obese women without
medical comorbidity.11,12,15,27 The risks of intrapartum and
postpartum complications and hospital referral or emergency
transfer along with cesarean birth risk should be carefully
evaluated and discussed with women with obese BMIs when
choosing place of birth. Pregnancy complicated by obesity
must be viewed holistically, with overall health considered
in addition to BMI measurement. Additional research ana-
lyzingperinataloutcomesforotherwisehealthywomenwith
different classes of obesity will allow for updated perinatal
care guidelines to reflect the breadth of potential outcomes
for women with obesity.
CONFLICT OF INTEREST
The authors have no conflicts of interest disclose.
ACKNOWLEDGMENTS
The authors wish to acknowledge the Yale University School
of Nursing for its support of Dr. Jevitt’s work during the writ-
ing of this article. All authors declare that they have no com-
peting interests. This study was partially funded by the Amer-
ican Association of Birth Centers Foundation and the Yale
University School of Nursing .
SUPPORTING INFORMATION
Additional supporting information may be found online in
the Supporting Information section at the end of the article.
Appendix S.VariablesAsDefinedintheAmericanAs-
sociation of Birth Centers Perinatal Data Registry
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