Is there a relationship between maternal exercise and easy delivery without C – Section?
• Null: The proportion of women who did maternal exercise and had normally delivery is 0.67.
• Alternative: The proportion of women who did maternal exercise and had normally delivery is greater than 0.67.
1 – Naturally, normal delivery is more common than caesarian delivery, thus the proportion cannot be expected to be equal to 0.5. Data from the Centers for Disease Control and Prevention for the year 2013 indicated that 0.67 of deliveries in the United States are by normal delivery.
Review of Related Literatures and Studies
2 – Rad and Jahanshiri (2013): Available online at com. Pelagia Research Library
European Journal of Experimental Biology, 2013, 3(2):78-85
ISSN. ISSN: 2248 –9215
CODEN (USA): EJEBAU. Effect of a period of exercise during pregnancy on certain delivery parameters
Lila Sabbaghian Rad and Ashraf Jahanshiri
Physical Education and Sports Sciences, Science and Research Branch, Islamic Azad University, Tehran, IRAN
Scientific advancements, especially in medicine, have minimized pregnancy discomforts and delivery risks.
However, pregnant women are always concerned with delivery and associated discomforts. This may be one of the
reasons for the large number of Caesarean section in Iran. One of the methods for making delivery easier is to
prepare the mother through exercises. Due to the importance of delivery, the present research is carried out to
examine the effect of a period of physical exercise on certain delivery parameter such as the duration of the first
(active) and second stages of labor, type of delivery, instrumental vaginal delivery, and birth weight. This study was
ex post facto or causal-comparative. The subjects were 55 healthy, primiparous women who were randomly
assigned to an experimental group (_ = 25) and a control group (_ = 30). The training protocol involved aerobic,
strengthening, and stretching exercises for 30-60 minutes, 2 days per week, and 22 weeks, beginning from the
14thweek of pregnancy. Kolmogorov-Smirnov test and Shapiro’s test were applied to examine the normal distribution
of the data. Also t-test for independent samples, Mann-Whitney U test, and chi-square test were applied for data
analysis at the 0.05 significance level. The results showed that the first stage of labor was significantly shorter in the
experimental group than the control group. Moreover, frequency of Caesarean section significantly decreased in the
experimental group. However, there were no significant differences between these groups in duration of the second
stage of labor, frequency of instrumental vaginal delivery, and birth weight. Based on the results, performing a set
of exercises during the second and third trimesters of pregnancy decreases the duration of the first stage of labor
and the frequency of Caesarean section. It is thus recommended that medical centers invest on training courses with
the proposed protocol to reduce some of the problems associated with childbirth.
make delivery easier thru exercises
period of physical exercise on certain delivery parameters such as type of delivery
55 healthy, primiparous women who were randomly assigned to an experimental 25 and control 30
training protocol involved aerobic, strengthening, and stretching exercises for 30-60 minutes, 2 days per week, and 22 weeks, beginning from the 14thweek of pregnancy
frequency of Caesarean section significantly decreased in the experimental group
3 – May, L.E. (2012). Chapter 2. Effects of maternal exercise on labor and delivery. L. E. May, Physiology of Prenatal Exercise and Fetal Development,
SpringerBriefs in Physiology, DOI: 10.1007/978-1-4614-3408-5_2,
_ The Author(s) 2012
Abstract Despite popular belief, exercise while pregnant does not initiate labor,
or preterm labor. Exercise is associated with delivering closer to the due date.
Further, maternal exercise is associated with either no change, or shorter labor and
delivery overall. Women who exercised had less complications during labor and
delivery than those who did not exercise. More importantly, measures of the fetus
during the labor and delivery process did not indicate fetal distress. Measures of
fetal distress showed either no difference or improvements related to exercise
exposure, such as increased apgar scores. Exercised mothers and their children had
shorter hospital stays relative to nonexercisers. Overall, these findings of possibly
shorter labor, less preterm labor, less complications, and decreased hospital stay all
add up to decreased health-care costs. Further research is needed in this area.
exercise while pregnant does not initiate labor or preterm labor but associated with delivery closer to the due dates, no relationship between mode of delivery and maternal activity during gestation (Sternfeld et al. 1995; Horns et al.
1996; Kennelly et al. 2002b; Magann et al. 2002; Barakat et al. 2009b),
research, however, has found participation in exercise while pregnant is associated
with lower rates of cesarean section and less complications (Curet et al. 1976; Dale
et al. 1982; Hall and Kaufmann 1987; Clapp 1990; Clapp and Capeless 1990; Hatch
et al. 1993). Women who exercise during pregnancy also report lower perceived
exertion during labor, than women who did not exercise (Rice and Fort 1991).
4 – SciMedCentral. Medical Joural of Obstetrics and Gynecology. Review Article.
Influence of Exercise Mode on Maternal, Fetal, and Neonatal Health Outcomes
Moyer C1 and May L2*
1Department of Health and Human Sciences, Bridgewater College, USA
2Department of Foundational Sciences and Research, East Carolina University, USA
Linda May, Department of Foundational Sciences and Research, East Carolina University, USA, Tel: 252- 737-7072; Fax: 252-737-7049; E-mail:
Submitted: 05 August 2014
Accepted: 21 August 2014
Published: 23 August 2014
© 2014 May et al.
Research has demonstrated aerobic exercise is safe and beneficial for mother, fetus, and neonate. Unlike aerobic exercise, little research has focused on the effects of resistance training during pregnancy. Preliminary studies have shown that acute resistance training is safe for pregnant women. It has been found to be effective in increasing lean body mass in pregnant woman. Research studying chronic resistance training during pregnancy has focused on delivery outcome rather than examining the chronic health effects or adaptations of resistance training exposure for the expectant mother. Additionally, scarce research has been done to examine the effects of acute maternal resistance training on the fetus, except to conclude that the fetus is not at an increased risk of distress during maternal resistance exercises.
Some researchers have studied circuit (aerobic and resistance) training on acute maternal responses or chronic adaptations during pregnancy. In response to prolonged circuit training during pregnancy, women who exercised more were less likely to have a Cesarean delivery and spent less time recovering in the hospital. Furthermore, research has not been completed on the fetal responses or adaptations as a result of acute or chronic maternal circuit training throughout pregnancy, except to report that birth weights are similar between exercising and control groups. Logically, if aerobic and resistance exercise programs individually are safe for the pregnant woman and her fetus, then a combination program would also be safe. Clearly, more research is needed and this article will summarize our current state of knowledge regarding exercise during pregnancy.
Rev. salud pública. 14 (5): 731-743, 2012.
Type of delivery and gestational age is not affected by pregnant Latin-American women engaging in vigorous exercise. A secondary analysis of data from a controlled randomized trial1.
Diana C. Pinzón¹, Katherine Zamora¹, Jorge H. Martínez¹, María E. Floréz-López², Ana C. Aguilar de Plata³, Mildrey Mosquera³ y Robinson Ramírez-Vélez4.
Received 17th May 2011/Sent for Modification 23th February 2012/Accepted 18th May 2012
Objective There is controversy concerning whether exercise during pregnancy may increase preterm delivery risk and type of delivery. The effect of pregnant Latin-American women engaging in vigorous exercise during the second and third trimester was examined regarding type of delivery and gestational age.
Materials and Methods This was a secondary analysis of data from a controlled randomized trial for determining the influence of physical exercise on pregnant women’s endothelial function. The study included 35 nulliparous women, gestational week 16-20 attending prenatal care at three tertiary hospitals in Colombia, who were randomly assigned to one of two groups. The experimental group engaged in aerobic exercise involving 55 % – 75 % maximum heart rate for 60 min, three times a week for 12 weeks. The control group engaged in their usual physical activity. Maternal weight, height, weight gain, blood pressure and type of delivery were recorded; gender, abdominal and head circumference (cm), weight (g), height (cm), vitality (Apgar score at 1 and 5 min) and gestational age at the time of delivery (in weeks, days) were recorded for the newborn.
Results There was no difference in type of delivery by the end of the 12-week program (p>0.05), nor regarding newborn anthropometric variables, Apgar score, or
maternal variables concerning weight, height, relative weight gain, blood pressure or weeks of gestation (p>0.05).
Conclusion The potential public health benefits of vigorous exercise were enormous. This study supported existing guidelines indicating that Latin-American women may begin or maintain an on-going exercise program during pregnancy
6 – REVISAO Review. Physical activity during pregnancy and
maternal-child health outcomes: a systematic
literature review. Michael Maia Schlüssel 1
Elton Bicalho de Souza 1
Michael Eduardo Reichenheim 2
Gilberto Kac 1
A systematic literature review was conducted to
investigate the effects of physical activity during
pregnancy on selected maternal-child health
outcomes. The search included articles published
from 1980 to 2005 in the MEDLINE and
LILACS databases using key words such as physical
activity, physical exercise, pregnancy, and
gestation. The methodological quality of 37 selected
articles was evaluated. It appears to be a
consensus that some light-to-moderate physical
activity is not a risk factor and may even be considered
a protective factor for some outcomes.
However, some studies found an association between
specific activities (e.g., climbing stairs or
standing for long periods) and inadequate birth
weight, prematurity, and miscarriage. Few studies
found an association between physical activity
and maternal weight gain, mode of delivery,
or fetal development. Further research is needed
to fill these gaps and provide guidelines on the
intensity, duration, and frequency of physical
activity during pregnancy.
7 – Exercise during pregnancy improves maternal glucose screen at 24 – 28 weeks: a randomized controlled trial
Ruben Barakat,1 Yaiza Cordero,1 Javier Coteron,1 Maria Luaces,2 Rocio Montejo2
Objective. The influence of an exercise programme performed by healthy pregnant women on maternal glucose tolerance was studied.
Study design. A physical activity (PA, land/aquatic activities) programme during the entire pregnancy (three sessions per week) was conducted by a qualified instructor. 83 healthy pregnant women were randomly assigned to either an exercise group (EG, n=40) or a control (CG, n=43) group. 50 g maternal glucose screen (MGS), maternal weight gain and several pregnancy outcomes were recorded.
Results. Significant differences were found between study groups on the 50 g MGS. Values corresponding to the EG (103.8±20.4 mg/dl) were better than those of the CG (126.9±29.5 mg/dl), p=0.000. In addition, no differences in maternal weight gain and no cases of gestational diabetes in EG versus 3 in CG (7%) (p>0.05) were found.
Conclusion A moderate PA programme performed during pregnancy improves levels of maternal glucose tolerance.
8 – Journal of midwifery and reproductive health. JMRH.mums.ac.ir.
The Effect of Birth Ball Exercises during Pregnancy on Mode of Delivery in Primiparous Women
Kobra Mirzakhani (MSc)1, Zahra Hejazinia (MSc)2*, Nahid Golmakani (MSc)3, Mohammad Ali Sardar (PhD)4, Mohammad Taghi Shakeri (PhD)5.
Sept 30, 2014
Background & aim: Considering the fact that cesarean section (c-section) poses greater risks of maternal and neonatal complications, compared to vaginal delivery, scholars seek different strategies to decrease the prevalence of this surgical procedure. Birth ball exercises during pregnancy are among the proposed strategies. Thus, this study aimed to determine the effect of using birth ball during pregnancy on mode of delivery in primiparous women.
Methods: This clinical trial was conducted on 54 women, referring to the maternity ward of Omolbanin Hospital. Subjects were randomly assigned to intervention and control groups. The intervention group performed birth ball exercises for 4-6 weeks; on the other hand, the control group only received routine care. Data were collected using questionnaires, forms of examination and observation, and checklists for recording exercise movements on a weekly basis. Chi-square, Fisher’s exact test, and Mann-Whitney U test were performed, using SPSS version 16.
Results: Rates of vaginal delivery and c-section in the intervention group were 92.6% and 7.4%, respectively, while the corresponding values in the control group were 66.7% and 33.3%, respectively. Chi-square showed a significant difference between the two groups in terms of mode of delivery (P=0.018).
Conclusion: Considering the significance of promoting vaginal delivery among women, performing birth ball exercises is recommended as a useful, non-pharmacological, and inexpensive strategy for reducing c-section rate.
Mirzakhani K, Hejazinia Z, Golmakani N, Sardar MA, Shakeri MT. Effect of Performing Birth Ball Exercises during Pregnancy on Mode of Delivery in Primiparous Women. Journal of Midwifery and Reproductive Health. 2015; 3(1): 269-275.
9 – Effects of aerobic exercise training on maternal and neonatal outcome: a
randomized controlled trial on pregnant women in Iran
Zahra Ghodsi, Maryam Asltoghiri
Objective: To assess the effect of aerobic exercise training on maternal and neonatal outcome
Methods: The case-control study was conducted between January and July, 2011. It was approved by the Research
Ethics Committee of Toyserkan Azad University, and data was collected at prenatal clinics and delivery centres
located in Hamedan, Iran. It comprised 80 pregnant women between 20-26 weeks of gestation randomly assigned
to two equal and matching groups of cases and controls. The intervention group did exercise continuously on a
bicycle ergometre for 15 minutes, three times a week; the intensity being 50-60% of maximal heart rate. The control
group did not do any exercise training. All information was obtained from the clinics, delivery centres, and from the
reports of delivery room midwives.
Results: No statistically significant difference was found between the two groups in gestational weight gain,
pregnancy length, mode of delivery, first and second stage of labour, perineal tear, and 1st and 5th min Apgar score.
Mean neonatal weight was significantly less in the intervention group than the control group (p<0.001).
Conclusion: Exercising on a bicycle ergometer during pregnancy seems to be safe for the mother and the neonate.
Keywords: Bicycle Ergometer, Pregnancy, Maternal outcome, Neonatal outcome. (JPMA 64: 1053; 2014)
10 – The Effect of Exercise During Pregnancy on Maternal Outcomes: Practical Implications for Practice
Beth Lewis; Melissa Avery; Ernestine Jennings; Nancy Sherwood; Brian Martinson; A. Lauren Crain
Abstract and Introduction
The American College of Obstetricians and Gynecologists recommends that women with low-risk pregnancies participate in moderate- intensity exercise during their pregnancy. Currently, only 15.1% of pregnant women exercise at the recommended levels, which is significantly lower than the general population’s 45%. One potential reason is that exercise during pregnancy is perceived as risky. In this article, the authors provide a critical review of the literature examining the effect of exercise on pre-eclampsia, gestational diabetes, weight gain, labor and birth, and other issues associated with pregnancy. Overall, the evidence indicates that exercise during pregnancy is safe and perhaps even reduces the risk of preeclampsia and gestational diabetes. The evidence for weight gain and labor and birth (rates of cesarean sections, duration of labor) is mixed. Unfortunately, much of the research examining exercise during pregnancy is observational, and the few randomized controlled trials that do exist are small and inadequately powered. Taken together, given the potential benefits of exercise during pregnancy and the lack of evidence for harmful effects on the mother and newborn, practitioners should encourage their healthy pregnant patients to exercise. Practical guidelines for recommending exercise to pregnant women are presented.
11 – From Medscape Education Clinical Briefs
Light Resistance Exercise During Pregnancy Does Not Affect Type of Delivery
News Author: Pauline Anderson
CME Author: Laurie Barclay, MD
Faculty and Disclosures
CME Released: 01/04/2010; Valid for credit through 01/04/2011
January 4, 2010 — Regular low-intensity resistance and toning exercises, performed by healthy, previously sedentary women during pregnancy, does not affect the type of delivery, a new study has found.
A resistance exercise program also did not affect the mean dilation, expulsion, and childbirth time and did not appear to affect the newborn infant’s overall health status.
“The 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,” write Ruben Barakat, PhD, from Universidad Politécnica de Madrid, in Madrid, Spain, and colleagues. The study appears in the December issue of the American Journal of Obstetrics & Gynecology.
The aim of the study was to investigate the effects of a supervised maternal exercise training program performed during the second and third trimesters of pregnancy in the type of delivery (normal, instrumental, or cesarean) and on dilation, expulsion, and childbirth time.
The trial included healthy but sedentary pregnant women of low to medium socioeconomic class from a primary care medical center in Madrid, Spain. The women ranged in age from 25 to 35 years, had singleton and uncomplicated gestation, and were not at high risk for preterm delivery. These women were randomly assigned to either a training group or a control group
Women in the exercise group participated in a training program that included 3 sessions per week starting at the beginning of the second trimester and continuing for approximately 26 weeks. Each exercise session consisted of a warm-up period of approximately 8 minutes, roughly 20 minutes of toning and light resistance exercises, and an 8-minute cool-down period.
The toning and joint mobilization exercises involved major muscle and joint groups (ie, shoulder shrugs and rotations, arm elevations, leg lateral elevations.) Exercises were performed with bar bells or resistance bands. Sessions were accompanied with music and were carried in an airy, well-lit room.
A qualified fitness specialist carefully supervised each training session. Heart rate was carefully and individually controlled and kept at 80% or less of age-predicted maximal heart rate value.
Women in the control group were asked to maintain their level of activity during the study period.
The final analysis included 72 women in the training group and 70 in the control group.
The study found that the percentages of women who had natural, instrumental, and cesarean delivery were similar for women in the training program (70.8%, 13.9%, and 15.3%, respectively) and those in the control group (71.4%, 12.9% and 15.7%, respectively).
There were still no differences after controlling for variables that might affect labor outcomes, such as prepregnancy body mass index, weight gain, age, smoking habits, and alcohol intake.
Resistance training improves muscular strength. “There is increasing evidence of the beneficial effects of muscular strength on the prevention of chronic disease and on the ability to cope with daily living activities,” the study authors write. “Other potential benefits of resistance training during pregnancy include decreased risk for insulin dependence in overweight women with gestational diabetes, better posture, prevention of low back pain, and strengthening of the pelvic floor.”
Guidelines from the American College of Obstetricians and Gynecologists promote regular exercise for pregnant women, including sedentary pregnant women, for its overall health benefits, including a possible decreased risk for gestational diabetes mellitus.
The authors note that there has been some concern in the past that regular exercise during pregnancy could challenge the homeostasis of the maternal-fetal unit and therefore affect the outcome of the pregnancy by inducing changes in visceral blood flow, body temperature, carbohydrate use, or shear-stress.
“Therefore our findings are of clinical relevance because, in pregnant women, the documented benefits that regular training has on the maternal health are not accompanied by a lower incidence of natural deliveries,” they write. Natural deliveries, they add, are generally preferred to cesarean delivery because of the maternal risks associated with cesarean deliveries, including infection, blood loss, and respiratory complications.
This study was supported in part by the program I3 2006 and by the postdoctoral research program EX-2007-1124, Ministerio de Educación y Ciencia, Spain.
Am J Obstet Gynecol. 2009;201:590.e1-590.e6.
Perceived increased risk for problems linked to exercise during pregnancy, such as early pregnancy loss or decreased placental circulation, has led clinicians to recommend that pregnant women reduce physical activity. During recent years, however, the number of women participating in regular exercise has increased.
Most scientific evidence to date supports the safety of exercise during pregnancy, with few negative effects of physical activity reported in healthy pregnant women. Physical activity during pregnancy may even be beneficial to the maternal-fetal unit and may help prevent hypertension and other maternal disorders. Several unanswered questions in this area remain to be addressed.
The goal of the study was to determine the effect of light-intensity resistance exercise training during the second and third trimester on delivery outcomes.
Study endpoints were the type of delivery (normal, instrumental, or cesarean) and dilation, expulsion, and childbirth time.
The study sample consisted of 160 previously sedentary and healthy pregnant women who were randomly assigned to either a training group (n = 80) or to a control group (n = 80).
Exercise training consisted mainly of light resistance and toning exercises.
The investigators recorded several maternal and newborn characteristics; delivery type; and dilation, expulsion, and childbirth times.
Several potential confounding variables that can affect labor outcome (eg, prepregnancy body mass index, gestational weight gain, age, previous parity, smoking habits, alcohol intake, number of hours standing, and epidural anesthesia) were appropriately taken into account.
The training group and the control group did not differ in these variables.
In the training group, the percentage of women who had normal, instrumental, or cesarean delivery was 70.8%, 13.9%, and 15.3%, respectively.
These percentages were similar in the control group (71.4%, 12.9%, and 15.7%, respectively).
The groups did not differ in mean dilation, expulsion, and childbirth times.
The newborn infant’s overall health status was not significantly different between groups.
The investigators concluded that light-intensity resistance training performed during the second and third trimester of pregnancy does not affect the type of delivery.
They also suggest that this study adds additional evidence to support the overall health benefits of supervised, light-moderate regular exercise for healthy pregnant women, with very few (if any) complications.
A randomized study shows that light-intensity resistance training performed during the second and third trimester of pregnancy does not affect the type of delivery in healthy, previously sedentary women. The percentages of women who had normal, instrumental, or cesarean delivery were similar in the training and control groups.
The training and control groups did not differ in mean dilation, expulsion, and childbirth times, and the newborn infant’s overall health status was not significantly different between groups. The investigators suggest that this study adds additional evidence to support the overall health benefits of supervised, light-moderate regular exercise for healthy pregnant women.
According to the study by Barakat and colleagues, which of the following statements about the effect of light-intensity resistance exercise training during the second and third trimester on type of delivery is correct?
Normal deliveries were significantly higher in the training group
Cesarean deliveries were significantly higher in the control group
Instrumental deliveries were significantly higher in the training group
Types of delivery did not differ significantly between groups
According to the study by Barakat and colleagues, which of the following statements about the effect of light-intensity resistance exercise training during the second and third trimester of pregnancy on dilation, expulsion, and childbirth times is not correct?
Mean childbirth time was similar in both groups
Mean dilation and expulsion times were similar in both groups
The newborn infant’s overall health status was not significantly different between groups
Potential confounding variables that can affect labor outcome differed significantly between groups
12 – Research obstetrics. www.ajog.org. type of delivery is not affected by light resistance and toning exercise training during during pregnancy: a randomizd controlled trial. ruben bakarat, jonatan r. ruiz , james r. stirling, maria zakynthinaki, alejandrp lucia. American Journal of Obstetrics & Gynecology DECEMBER 2009
OBJECTIVE: We examined the effect of light-intensity resistance exercise
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.
STUDY DESIGN: We randomly assigned 160 sedentary women to either a
training (n_80) or a control (n_80) group.Werecorded several maternal
and newborn characteristics, the type of delivery (normal, instrumental, or
cesarean), and dilation, expulsion, and childbirth time.
RESULTS: The percentage of women who had normal, instrumental, or
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.
CONCLUSION: Light-intensity resistance training that is performed over
the second and third trimester of pregnancy does not affect the type of
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.
13 – Physical exercise during pregnancy and its
influence in the type of birth
Exercício físico durante a gestação e sua influência no tipo de parto
Lílian Cristina da Silveira1, Conceição Aparecida de Mattos Segre2
Objective: To verify if medium intensity exercise performed during
pregnancy can influence in the type of delivery, and to observe
compliance to an exercise program among primiparous women
with different levels of schooling. Methods: A study carried out at
the Centro de Incentivo ao Aleitamento Materno, in São Sebastiao
(SP), between April 7, 2008, and April 14, 2009. A prospective study
involving 66 primiparous women who were divided into two groups: an
Exercise Group, engaged in regular physical activity during pregnancy,
and the Control Group, that did not participate in regular physical
activity during the same period. Significance level in this project was
5% (p=0.05). Results: The group that did engage in regular exercise
had a higher rate of vaginal deliveries, with a statistically significance
difference evaluated by the 2 test (p=0.031). The pregnant women
with the highest level of schooling showed greater compliance
with the exercise program, with a statistically significant difference
(p=0.01736). Conclusion: Physical exercise in primiparous women
increased the chances of vaginal deliveries, and there was greater
compliance with the exercise program among those with a higher
level of schooling when compared to those with a basic education.
1 – Centers for Disease Control and Prevention (http://www.cdc.gov/nchs/fastats/delivery.htm) . Births – Method of Delivery. Data for US.
2 – http://pelagiaresearchlibrary.com/european-journal-of-experimental-biology/vol3-iss2/EJEB-2013-3-2-78-85.pdf (Effect of a Period of Exercise during pregnancy on certain delivery parameters)
3 – http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1004&context=hhstheses
4 – http://www.jscimedcentral.com/Obstetrics/obstetrics-2-1036.pdf
5 – http://www.scielosp.org/pdf/rsap/v14n5/v14n5a01.pdf
6 – http://www.scielo.br/pdf/csp/v24s4/06.pdf
7 – http://oa.upm.es/16796/2/INVE_MEM_2012_137308.pdf
8 – http://jmrh.mums.ac.ir/article_3562_548.html
9 – http://www.jpma.org.pk/full_article_text.php?article_id=6934
10 – www.preggibellies.com.au/uploads/GMHmG_OS4xyDrJjhcqpQQ27S.doc
11 – http://www.medscape.org/viewarticle/714541
12 – http://www.ajog.org/article/S0002-9378(09)00624-3/abstract?cc=y
13 – http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-45082012000400003