Research
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OBSTETRICS
Type of delivery is not affected by light resistance
and toning exercise training during pregnancy:
a randomized controlled trial
Ruben Barakat, PhD; Jonatan R. Ruiz, PhD; James R. Stirling, PhD; María Zakynthinaki, PhD; Alejandro Lucia, MD, PhD
OBJECTIVE: We examined the effect of light-intensity resistance ex-
RESULTS: The percentage of women who had normal, instrumental, or
ercise training that is performed during the second and third trimester of pregnancy by previously sedentary and healthy women on
the type of delivery and on the dilation, expulsion, and childbirth
time.
cesarean delivery was similar in the training (70.8%, 13.9%, and
15.3%, respectively) and control (71.4%, 12.9%, and 15.7%, respectively) groups. The mean dilation, expulsion, and childbirth time did not
differ between groups.
STUDY DESIGN: We randomly assigned 160 sedentary women to either a training (n ⫽ 80) or a control (n ⫽ 80) group. We recorded
several maternal and newborn characteristics, the type of delivery
(normal, instrumental, or cesarean), and dilation, expulsion, and
childbirth time.
CONCLUSION: Light-intensity resistance training that is performed over
the second and third trimester of pregnancy does not affect the type of
delivery.
Key words: cesarean delivery, resistance training, vaginal delivery
Cite this article as: Barakat R, Ruiz JR, Stirling JR, et al. Type of delivery is not affected by light resistance and toning exercise training during pregnancy: a
randomized controlled trial. Am J Obstet Gynecol 2009;201:590.e1-6.
P
regnant women have been encouraged traditionally to reduce physical
activity because of perceived increased
risk of problems, such as early pregnancy
loss or reduced placental circulation.1
The number of women who engage in
regular exercise (or who are willing to
From Facultad de Ciencias de la Actividad
Física y del Deporte–INEF, Universidad
Politécnica de Madrid, Spain (Drs Barakat
and Stirling) and Instituto de Ciencias
Matemáticas, CSIC-UAM-UC3M–UCM,
Madrid, Spain, (Dr Zakynthinaki), and
Universidad Europea de Madrid, Spain (Dr
Lucia), and the Department of Biosciences
and Nutrition at NOVUM, Unit for
Preventive Nutrition, Karolinska Institutet,
Huddinge, Sweden (Dr Ruiz).
Received Nov. 6, 2008; revised Dec. 5, 2008;
accepted June 1, 2009.
Reprints not available from the authors.
This work was supported in part by the
program I3 2006 and by the postdoctoral
research program EX-2007-1124, Ministerio
de Educación y Ciencia, Spain.
The first 2 authors contributed equally to the
preparation of this manuscript.
0002-9378/$36.00
© 2009 Mosby, Inc. All rights reserved.
doi: 10.1016/j.ajog.2009.06.004
590.e1
do so) during pregnancy, however, has
increased in the last years.2 This tendency is overall supported by the bulk of
scientific evidence. Several publications
over the last decade have reported few
negative effects of physical activity
on the pregnancy of a healthy pregnant
woman.3-6 Further, physical activity
during pregnancy could be beneficial to
the maternal-fetal unit and prevent the
occurrence of maternal disorders, such
as hypertension.7 Recent guidelines by
the American College of Obstetricians
and Gynecologists promotes regular exercise for pregnant women, including
sedentary ones, for its overall health benefits, which includes possibly a decreased
risk of gestational diabetes mellitus.8,9
Obstetricians lack sufficient information to provide constructive guidance for
their patients who want to be physically
active over the entire pregnancy, because
several questions remain to be answered.
One important question that frequently
is addressed relates to the possibility that
high physical activity levels, especially
during the second part of pregnancy,
might affect main gestational outcomes,
which would include gestational age and
type of delivery. Data from noncontrolled10 and controlled training studies
American Journal of Obstetrics & Gynecology DECEMBER 2009
on small11 or large12 population samples
and from prospective reports on large
population samples showed no association between physical activity during
pregnancy and gestational age, risk
of preterm delivery, or intrauterine
growth.3,13-18 Less data are available on
the association between physical activity
during pregnancy and the type of delivery. A prospective study showed that, in
previously well-conditioned women,
continuation of their exercise regimens
(aerobics or running) during the second
half of pregnancy had a beneficial effect
on the course and outcome of labor (ie,
lower incidence of abdominal and normal [vaginal] operative delivery).19 This
is in agreement with prospective data on
previously sedentary nulliparous women
that shows that regular participation in
aerobic exercise during the first 2 trimesters of pregnancy can be associated with
reduced risk for cesarean delivery.20 In a
study by Hall and Kaufmann,21 845
women were given the option to participating or not in a prenatal exercise program of different intensities that involved weight-lifting and stationary
bicycling. The proportion of vaginal deliveries increased with the intensity of
the program.
Obstetrics
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FIGURE
Flow diagram of the study participants
Assessed for eligibility (n = 480)
Excluded from the study (n = 320)
Not meeting inclusion criteria (n = 199)
Refused to participate (n = 121)
Other reasons (n = 0)
Enrollment
Randomized (n = 160)
Allocation
Follow-up
Analysis
Allocated to intervention (n = 80, training)
Received intervention (n = 80)
Did not receive intervention (n = 0)
Allocated to intervention (n = 80, controls)
Received intervention (n = 80)
Did not receive intervention (n = 0)
Lost to follow-up (n = 0)
Discontinued intervention (n = 8)
Risk for premature labour (n = 1)
Pregnancy-induced hypertension (n = 1)
Persistent bleeding (n = 1)
Personal reasons (n = 5)
Lost to follow-up (n = 5)
Discontinued intervention (n = 5)
Gave birth in a different hospital (n = 5)
Pregnancy-induced hypertension (n = 2)
Threat of premature delivery (n = 2)
Molar pregnancy (n = 1)
Analyzed (n = 72)
Excluded from analysis (n = 0)
Analyzed (n = 70)
Excluded from analysis (n = 0)
Barakat. Delivery not affected by exercise training. Am J Obstet Gynecol 2009.
Randomized, controlled training trials
in large population samples, however,
are lacking to objectively and specifically
assess the possible cause– effect relationship between exercise interventions during the second half of pregnancy and the
type of delivery. Accordingly, it was the
purpose of our study to investigate the
effects of a supervised maternal exercise
training program (performed during the
second and third trimesters of pregnancy) on the type of delivery (normal,
instrumental, or cesarean) and on dilation, expulsion, and childbirth time. A
matched control group was assessed over
the same time period. Given that most
studies in the field have used aerobic exercise, we largely focused on resistance
and toning exercises. Resistance exercise
training increases muscular strength and
is prescribed currently by sound medical
organizations for improving health and
fitness.22-25
M ETHODS
The present study was a randomized,
controlled training trial. A complete description of design and methods has
been published elsewhere.12 We contacted a total of 480 Spanish (white)
pregnant women of low-to-medium so-
cioeconomic class, from a primary care
medical center (Centro de Salud María
Montesori, Leganés, Madrid, Spain; Figure). A total of 160 healthy pregnant
women who were 25-35 years old, who
were sedentary (not exercising ⬎20 minutes on ⬎3 days per week), who had singleton and uncomplicated gestation, and
who were not at high risk for preterm
delivery (no more than 1 previous preterm delivery) were assigned randomly
to either a training or control group (n ⫽
80 each).
The participant randomization assignment followed an allocation concealment
process.26,27 The researcher in charge of
randomly assigning participants did not
know in advance which treatment the next
person would receive and did not participate in assessment. Assessment staff members were blinded to participant randomization assignment, and participants were
reminded to not to discuss their randomization assignments with assessment staff
members.
All the participants were informed
about the aim and study protocol, and all
the women provided written informed
consent. Women who were not planning
to give birth in the same obstetrics hospital department (Hospital Severo
Research
Ochoa, Madrid, Spain) and not be under
medical follow-up throughout the entire
pregnancy period were not included in
the study. Women who had any serious
medical condition that prevented them
from exercising safely were not included
in the study.8
The research protocol was reviewed
and approved by the Hospital Severo
Ochoa (Madrid, Spain). The study was
performed between January 2000 and
March 2002 and followed the ethical
guidelines of the Declaration of Helsinki,
which was last modified in 2000.
Control and intervention groups
Women in the nonexercise control
group were asked to maintain their level
of activity during the study period. All
participants were followed throughout
the entire pregnancy period.
Details of the exercise training protocol have been described by Barakat et
al.12 Women in the training group were
enrolled in 3 sessions per week for approximately 26 weeks. Heart rate was
carefully and individually controlled
(Accurex Plus; Polar Electro OY, Finland) through every session and was kept
at ⱕ80% of age-predicted maximum
heart rate value (220 minus the woman’s
age).
The exercise training program started
in the beginning of the second trimester
(week 12-13) and was prolonged until
the end of the third trimester (week 3839). We originally planned an average of
approximately 80 training sessions for
each participant in the event of no preterm delivery. Each exercise training session consisted of a warm-up period of
approximately 8 minutes (ⱕ60% maximum heart rate value), approximately 20
minutes of toning and very light resistance exercises (ⱕ80% maximum heart
rate value), and a cool-down period of
approximately 8 minutes (ⱕ60% maximum heart rate value).
The core portion consisted of toning
and joint mobilization exercises that involved major muscle and joint groups
(ie, shoulder shrugs and rotations, arm
elevations, leg lateral elevations, pelvic
tilts, and rocks). Resistance exercises
were performed with barbells (ⱕ3 kg per
exercise) or low-to-medium resistance
DECEMBER 2009 American Journal of Obstetrics & Gynecology
590.e2
Research
Obstetrics
bands (Thera-band; The Hygienic Corporation, Akron, OH) and included 1 set
of ⱕ10-12 repetitions of abdominal
curls, biceps curls, arm extensions, arm
side lifts, shoulder elevations, seated
bench press, seated lateral row, lateral leg
elevations, leg circles, knee extensions,
knee (hamstring) curls, and ankle flexion and extensions. Supine postures and
exercises that involved extreme stretching and joint overextension, ballistic
movements, jumps, and those types of
exercises that are performed on the back
were specifically avoided. To minimize
cardiovascular stress, we specifically instructed participants to avoid the Valsalva maneuver.
To reduce participants drop out and to
maintain adherence to the training program, all sessions were accompanied
with music and were performed in an
airy, well-lighted exercise room. A qualified fitness specialist carefully supervised every training session and worked
with groups of 10-12 women. We used
the exercise training facilities from the
primary care medical center where they
were monitored through the pregnancy.
No women changed from the control
group to the intervention group or vice
versa.
Type of delivery and other
outcome measures
We obtained type of delivery (normal,
instrumental, and cesarean); dilation,
expulsion, and childbirth time; use (or
not) of epidural anesthesia, and Apgar
scores (at 1 and 5 minutes) from the reports of delivery room personnel (midwife). We recorded birthweight, birth
length, and head circumference of the
newborn infant and gestational age at
time of delivery (in weeks, days) from
hospital perinatal records. The results of
Apgar scores and gestational age have
been recently reported.12
We used the Minnesota Leisure-Time
physical activity questionnaire to assess
the occupational activities and other
daily activities, such as number of hours
standing.28 We measured weight and
height of the mother by standard procedures at the start of the study and before
parity and eventual preterm deliveries,
which is ⬍37 completed weeks of gesta590.e3
www.AJOG.org
tion. Body mass index was calculated as
weight (in kilograms) divided by height
(in meters) squared. Smoking habits and
alcohol intake at the start of the study
and previous parity were recorded
through an interview.
Statistical analyses
We used a conservative approach to
sample size estimation. We made power
calculations for the primary outcome
measures of gestational age, Apgar score,
birthweight, and length. We determined
that adequate power (⬎0.80) would be
achieved with 70 pregnant women in the
training group and with 70 pregnant
women in the control group. All power
computations assumed that comparisons of baseline to 26-week scores would
be tested at the 5% significance level. All
power computations allowed for 10%
dropouts over 26 weeks.
We presented maternal and newborn
infant characteristics of the study sample
by group (training and control) as means
and standard deviations (SD), unless
otherwise stated. For group comparisons, we analyzed continuous and nominal data with t test for unpaired data and
␹2 tests, respectively. We compared Apgar scores between groups using the
nonparametric Mann-Whitney U test.
Multiple comparisons were adjusted for
mass significance as described by
Holm.29 All statistical analyses were performed with the Statistical Package for
Social Sciences software (version 14.0 for
Windows; SPSS Inc, Chicago, IL); the
level of significance was set to ⬍ .05.
R ESULTS
The final number of participants that we
included as valid study pregnant women
was 72 in the training group and 70 in the
control group (Figure). There were no
exercise-related injuries experienced
during pregnancy, nor were there any
cases of gestational diabetes mellitus.
The return for follow-up evaluation was
⬎90% for both training and control
groups. We noted no major adverse effects and no major health problems in
the participants, except for 2 preterm deliveries in the training group and 3 preterm deliveries in the control group.
Women in the training group were
American Journal of Obstetrics & Gynecology DECEMBER 2009
rather pleased with the exercise training,
and all of the women reported their intention to be physically active in future
pregnancies. There were no protocol deviations from study as planned.
Table 1 shows the maternal and newborn infant characteristics in the training
and control groups. We did not observe a
significant difference between groups in
any of the variables that were studied (all
P ⬎ .1). The type of delivery and labor
times in the training and control group
are shown in Table 2. The percentage of
women who had natural, instrumental,
and cesarean delivery was similar (P ⬎
.1) in the training (70.8%, 13.9%, and
15.3%, respectively) and control group
(71.4%, 12.9%, and 15.7%, respectively). Likewise, the mean dilation, expulsion, and childbirth time did not differ between groups (all P ⬎ .1).
C OMMENT
The main finding of the present randomized controlled trial was that supervised
resistance and toning exercise training
that is performed over the second and
third trimester of pregnancy does not affect the type of delivery nor the mean dilation, expulsion, and childbirth time in
previously sedentary healthy pregnant
women. Furthermore, we did not observe any effect on the newborn infant’s
overall health status. To strengthen our
findings, several potential confounding
variables that can affect labor outcome
(such as prepregnancy body mass index,
gestational weight gain age, previous
parity history, smoking habits, alcohol
intake, number of hours standing, and
epidural anesthesia) were appropriately
taken into account. Indeed, we did not
observe differences between the training
and the control group in the aforementioned variables.
The mode of exercise training that was
followed by the intervention group and
the relatively large number of previously
sedentary healthy pregnant women who
were enrolled in the study are additional
strengths of our study. Exercise training
consisted mainly of light resistance and
toning exercises. Except in the nonrandomized training study by Hall and
Kaufmann,21 most previous studies ana-
Obstetrics
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Research
TABLE 1
Characteristics in the training and control groups
Characteristic
Training group (n ⴝ 72)
Control group (n ⴝ 70)
Maternal age (y)a
30.4 ⫾ 2.9
29.5 ⫾ 3.7
Body mass index (kg/m )
24.3 ⫾ 0.5
23.4 ⫾ 0.5
................................................................................................................................................................................................................................................................................................................................................................................
2 a,b
................................................................................................................................................................................................................................................................................................................................................................................
Previous gestation (n)
.......................................................................................................................................................................................................................................................................................................................................................................
0
52 (72.2%)
40 (57.1%)
1
16 (22.2%)
25 (35.7%)
2
4 (5.6%)
5 (7.1%)
.......................................................................................................................................................................................................................................................................................................................................................................
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Smoking habits (n)
.......................................................................................................................................................................................................................................................................................................................................................................
Yes
16 (22.2%)
20 (28.6%)
No
56 (77.8%)
50 (71.4%)
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Alcohol intake (n)
.......................................................................................................................................................................................................................................................................................................................................................................
Yes
3 (4%)
5 (7%)
No
69 (96%)
65 (93%)
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Occupational activity (n)
.......................................................................................................................................................................................................................................................................................................................................................................
Sedentary job
26 (36.1%)
21 (30.0%)
Housewife
31 (43.1%)
30 (42.9%)
Active job
15 (20.8%)
19 (27.1%)
.......................................................................................................................................................................................................................................................................................................................................................................
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Hours standing (n)
.......................................................................................................................................................................................................................................................................................................................................................................
⬎3 h
34 (47.2%)
46 (65.7%)
⬍3 h
38 (52.8%)
24 (34.3%)
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Maternal education (n)
.......................................................................................................................................................................................................................................................................................................................................................................
⬍High school
25 (34.7%)
31 (44.3%)
High school
28 (38.9%)
30 (42.9%)
⬎High school
19 (26.4%)
9 (12.9%)
.......................................................................................................................................................................................................................................................................................................................................................................
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Previous miscarriage (n)
.......................................................................................................................................................................................................................................................................................................................................................................
0
59 (81.9%)
58 (82.9%)
1
10 (13.9%)
11 (15.7%)
2
3 (4.2%)
1 (1.4%)
.......................................................................................................................................................................................................................................................................................................................................................................
.......................................................................................................................................................................................................................................................................................................................................................................
................................................................................................................................................................................................................................................................................................................................................................................
Previous low birthweight newborn infant: ⬍2500 g (n)
.......................................................................................................................................................................................................................................................................................................................................................................
0
72 (100%)
68 (97.1%)
.......................................................................................................................................................................................................................................................................................................................................................................
1
0
2 (2.9%)
2 (2.8%)
3 (4.3%)
................................................................................................................................................................................................................................................................................................................................................................................
c
Preterm deliveries (⬍37 weeks) by the end of the study (n)
................................................................................................................................................................................................................................................................................................................................................................................
ab
Weight gain during pregnancy (kg)
11.5 ⫾ 3.7
12.4 ⫾ 3.4
................................................................................................................................................................................................................................................................................................................................................................................
a
Birthweight (g)
3165 ⫾ 411
3307 ⫾ 477
................................................................................................................................................................................................................................................................................................................................................................................
a
Birth length (cm)
49.5 ⫾ 1.8
49.7 ⫾ 1.8
................................................................................................................................................................................................................................................................................................................................................................................
Apgar score
.......................................................................................................................................................................................................................................................................................................................................................................
a
1 min
8.9 ⫾ 1.1
8.8 ⫾ 1.2
5 min
9.9 ⫾ 0.2
9.9 ⫾ 0.3
39/4 ⫾ 1/2
39/5 ⫾ 1/2
.......................................................................................................................................................................................................................................................................................................................................................................
a
................................................................................................................................................................................................................................................................................................................................................................................
a
Gestational age (wk/d)
................................................................................................................................................................................................................................................................................................................................................................................
a
Data are expressed as mean ⫾ SD. We analyzed continuous and nominal data with t test for unpaired data and chi-square tests, respectively; all group comparisons were nonsignificant, with a
probability value of ⬎ .1; b there are 6 missing sets of data in the control group that refer to prepregnancy weight and height; c there were no women with ⬎1 previous preterm delivery.
Barakat. Delivery not affected by exercise training. Am J Obstet Gynecol 2009.
DECEMBER 2009 American Journal of Obstetrics & Gynecology
590.e4
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TABLE 2
Type of delivery and labor times in the training and control groups
Variable
Training group
(n ⴝ 72)
Control group
(n ⴝ 70)
P value
⬎ .1
Type of delivery
.....................................................................................................................................................................................................................................
Natural (n)
51 (70.8%)
50 (71.4%)
Instrumental (n)
10 (13.9%)
9 (12.9%)
Cesarean (n)
11 (15.3%)
11 (15.7%)
50 (69.4%)
48 (68.6%)
.....................................................................................................................................................................................................................................
.....................................................................................................................................................................................................................................
..............................................................................................................................................................................................................................................
Epidural anesthesia (n)
⬎ .1
..............................................................................................................................................................................................................................................
a
Dilation time (min)
426 ⫾ 20
378 ⫾ 13
⬎ .1
..............................................................................................................................................................................................................................................
a
Expulsion time (min)
32.5 ⫾ 24.7
36.0 ⫾ 31.5
⬎ .1
Childbirth time (min)
8.1 ⫾ 2.3
7.7 ⫾ 1.7
⬎ .1
esthesia, or longer hospitalization periods)
and its higher medical cost.20
In summary, regular supervised exercise training (which consists of light resistance and toning exercises) that are
performed over the second and third trimester of pregnancy does not affect delivery type in previously sedentary
women. This study adds further evidence to support the overall health benefits of supervised, light-moderate regular exercise for healthy pregnant women
with very few (if any) complications. f
..............................................................................................................................................................................................................................................
a
..............................................................................................................................................................................................................................................
a
Data are expressed as mean ⫾ SD.
Barakat. Delivery not affected by exercise training. Am J Obstet Gynecol 2009.
lyzed the effect of aerobic exercise on
pregnancy outcomes.10,13-20,30
Even of low intensity (as here) resistance exercise should be an integral component of any exercise training program.
Indeed, increased muscle strength that is
induced by resistance training (eg, as in
the trained group here) results in an attenuated cardiovascular stress response
to any given load during physical activities of daily living because the load now
represents a lower percentage of the
maximal voluntary contraction.31 There
is increasing evidence of the beneficial
effects that improved muscular strength
has on the prevention of chronic diseases
and on the ability to cope with daily living activities in both healthy and diseased people.32,33 Regular resistancetype physical activities, such as the ones
performed by our training group, are
main determinants of muscular strength
and are recommended for improving
public health by major medical organizations.22,23,25,33 Other potential benefits
of resistance training during pregnancy
include decreased risk of insulin dependence in overweight women with gestational diabetes mellitus34 and also better
posture, prevention of gestational low
back pain and diastasis recti, and
strengthening of the pelvic floor.35,36
Our results show no differences in
type of delivery between both groups are
in apparent disagreement with previous
data from prospective19,20,35 or training21 studies that have suggested that
regular exercise that is performed over
590.e5
the course of pregnancy is associated
with an increased incidence of vaginal
delivery. Comparisons between studies,
however, are difficult to make because of
differences in several variables that can
affect delivery type, such as age, body
mass index, gestational weight gain age,
previous parity history, smoking habits,
alcohol intake, number of hours standing, and epidural anesthesia. In any case,
the cross-sectional19,20,37 or nonrandomized21 nature of previous studies
precludes a true cause– effect relationship from being established between exercise and type of delivery. Further, the
etiologic mechanisms behind this reported association remain to be
elucidated.
Regular sustained exercise during
pregnancy traditionally has been a cause
of concern because it could potentially
challenge the homeostasis of the maternal-fetal unit; thus, it might affect adversely the course and outcome of pregnancy (ie, by inducing changes in
visceral blood flow, body temperature,
carbohydrate use, or shear-stress).2,19,30,38
Therefore, our findings are of clinical relevance because, in pregnant women, the
documented benefits that regular training
has on the maternal health status38,39 are
not accompanied by a lower incidence of
natural deliveries. This type of delivery is
generally preferred to cesarean section delivery because of the maternal risks of the
latter (eg, infection, excessive blood loss,
respiratory complications, reactions to an-
American Journal of Obstetrics & Gynecology DECEMBER 2009
ACKNOWLEDGMENT
We thank the Gynecology and Obstetric Service of Severo Ochoa Hospital of Madrid for
technical assistance.
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