Yoga is increasing in popularity in the United States and has become a mainstream form of exercise practiced by more than 20 million Americans in 2012 as compared with approximately 16 million in 2008.1 Women are interested in participating in yoga during their pregnancy.2 The American College of Obstetricians and Gynecologists recommends pregnant women should be encouraged to engage in regular moderate intensity physical activity in the absence of contraindications.3 Research supports moderate-intensity physical activity during pregnancy.4 In 2008, the U.S. Department of Health and Human Services provided physical activity guidelines including those for pregnant women.5 Yoga was listed as an example of a health-enhancing physical activity and has been described as a moderate-intensity exercise.5,6 5,6
Many studies have examined the benefits of yoga in pregnancy.7–11 7–11 7–11 7–11 7–11 However, there are no evidence-based studies examining maternal and fetal safety in specific yoga postures (PubMed; 1979 to May 2015; English Language; search terms: “yoga,” “pregnancy,” and “exercise”). Popular yoga web sites have advised there are certain postures that are contraindicated in pregnancy such as Child's Pose, Corpse Pose, Downward Facing Dog, and Happy Baby Pose.12,13 12,13 We could not identify any scientific evidence to support these concerns (PubMed; 1949 to May 2015; English Language; search terms: “yoga,” “Child's Pose,” “Corpse Pose,” “Downward Facing Dog,” and “Happy Baby Pose”). The purpose of our study was to evaluate acute maternal and fetal responses to common yoga postures, including suspected contraindicated postures.
MATERIALS AND METHODS
We conducted a prospective study to evaluate acute maternal and fetal responses to a single session of yoga postures in pregnancy. Pregnant women between 35 0/7 and 37 6/7 weeks of gestation and age 18–42 years old with an uncomplicated gestation were recruited. Participants were excluded for chronic hypertension, preeclampsia or gestational hypertension, ruptured membranes, premature labor during current pregnancy, placenta previa after 26 weeks of gestation or placenta accreta, second- or third-trimester bleeding, incompetent cervix or cervical cerclage, multiple gestations, fetal growth restriction, oligohydramnios, diabetes or gestational diabetes, body mass index (BMI, calculated as weight [kg]/height [m]2) greater than 35, and any other medical contraindications to exercise.
The study was presented at the Jersey Shore University Medical Center, Department of Obstetrics and Gynecology, monthly meeting with a request for physicians and midwives to identify pregnant women for recruitment. Once an interested woman was identified, the primary investigator or subinvestigator contacted the participant and reviewed her medical and obstetric history. The Meridian Health institutional review board approved the protocol and all participants were provided written informed consent. Participation in the study was voluntary.
The one-on-one yoga session was conducted in a labor room on the labor and delivery unit at Jersey Shore University Medical Center. A certified yoga instructor, obstetrics and gynecology resident, and board-certified obstetrician–gynecologist were in attendance during the yoga session. Participants first completed a nonstress test. Maternal vital signs and pulse oximetry were assessed.
The 26 postures selected for this study are a group of standard postures found in a typical yoga class (Appendix 1, available online at http://links.lww.com/AOG/A715). Postures included standing, sitting, and supine positioning and incorporated twisting, balancing, bending, and stretching. Postures in the prone position were excluded to avoid pressure on the gravid uterus. Inversion postures such as head or handstand were excluded because of fall risk.
Maternal and fetal well-being was continuously monitored using blood pressure (BP), heart rate, pulse oximetry, uterine tocometry, and fetal heart tracing during the 26 yoga postures. Safety parameters were based on established exercise criteria. By protocol, if values were outside the established range, the study would be terminated. Systolic BP was not to exceed a peak value of 200 mm Hg and diastolic not to exceed a peak of 100 mm Hg.14 Each participant's estimated maximum heart rate was calculated and this number was used to determine the maximum allowable pulse rate.15 Pulse oximetry values of less than 94% precluded continuation in the study. Fetal heart tracings were interpreted based on the American College of Obstetricians and Gynecologists clinical management guidelines for intrapartum fetal heart rate tracings.16 The fetal heart rate baseline was measured continuously using the normal 110–160 beats per minute range.16 Sessions were to be discontinued per request for evidence of maternal intolerance, abnormal fetal heart tracing, or regular contractions.
To avoid injury, modifications were used to assist women in the yoga postures. Some yoga postures (Extended Side Angle Pose, Extended Triangle Pose, Warrior III, Tree Pose, Garland Pose, Eagle Pose, and Half Moon Pose) incorporated modifications with the use of blocks, chairs, and the wall to aid in body alignment and safety. The flow from each posture was continuous with each posture held for a total of 2 minutes. The postures were released sooner if the participant reported discomfort. Time was allowed for resting between postures if the participant needed a break.
At the completion of the yoga session, a nonstress test, vital signs, and pulse oximetry were reevaluated. Participants were contacted through e-mail 24 hours after the yoga session. They were asked about fetal movement, contractions, leakage of fluid, vaginal bleeding, discomfort after exercise, and overall yoga experience.
Because there was no prior study to explore this topic, we aimed to recruit 25 participants so that the upper limit of a one-sided 95% confidence interval for the chance of having an adverse event (eg, abnormal fetal heart rate tracing) would be 11.3%.17
Mean and standard deviation were used to summarize participant characteristics and measurements, which were continuous variables. Frequency, percentage, median, and quartiles were used to summarize the discrete variables. Shapiro-Wilk test was used to test the normality of continuous variables. Wilcoxon signed-rank test was used to compare the changes of continuous variables from the baseline to the end of the yoga postures. Kruskal-Wallis one-way analysis of variance by rank was used to compare the continuous or discrete variables among groups. Fisher's exact test was used to compare the categorical variables among groups. The two-sided P values from all tests were reported. A P value of ≤.05 indicated statistical significance. The statistical software package R language was used for data analysis.
Thirty women were enrolled in the study. Five were excluded for regular contractions on tocometry at the initial nonstress test. Twenty-five women completed the yoga session. Ten (40%) participated in a regular yoga practice, eight (32%) were familiar with yoga, and seven (28%) had no yoga experience. All participants completed the 26 postures. Table 1 identifies the characteristics of all participants and pregnant women were grouped based on their yoga experience. All groups were similar in age, parity, race, gestational age, and BMI.
Presession diastolic BP, maternal heart rate, temperature, and pulse oximetry were normal and all nonstress tests reactive (Table 2). No statistically significant differences among the groups were noted. There was a statistically significant difference in systolic BP among yoga groups.
There were no falls or injuries during the total cumulative 650 postures. Maternal vital signs, pulse oximetry, and uterine tocometry remained normal in all participants and in all postures. No participant had a systolic BP greater than 200 mm Hg, exceeded her maximum allowable pulse rate, had a pulse oximetry value of less than 94% shown (see Appendix 2, available online at http://links.lww.com/AOG/A716), or had regular contractions.
The baseline fetal heart rate during postures was 110–160 beats per minute. There were fetal accelerations above baseline with the fetal heart rate reaching above 180 beats per minute but no sustained tachycardia (Appendix 3, available online at http://links.lww.com/AOG/A717). There was no fetal bradycardia or decelerations.
In the suspected contraindicated yoga postures (Child's Pose, Corpse Pose, Downward Facing Dog, and Happy Baby Pose), maternal vital signs, pulse oximetry, and tocometry were normal. The fetal heart tracing remained category 1 in these postures.
All participants' postsession nonstress tests were reactive. Table 3 shows the postsession maternal vital signs, pulse oximetry, and fetal heart rate. Postsession systolic BP, maternal heart rate, temperature, and pulse oximetry were normal and fetal heart rate was reactive. There were no persistent elevation in systolic or diastolic BPs, no maternal sustained tachycardia, no fever, and no oxygen desaturation. It took approximately 2 hours for participants to complete the study. The level of yoga experience was not associated with the time it took to complete all postures. There was no statistical difference among groups in the total time the yoga session took to complete (regular yoga practice 115±11 minutes, familiarity with yoga 110±13 minutes, no yoga experience 115±13 minutes, P=.758).
All participants responded to an e-mail sent 24 hours after the yoga session. No participants felt unsafe during the session. No participants reported leakage of fluid, vaginal bleeding, contractions, or decreased fetal movement. Twenty-two (88%) participants used only positive descriptions for their yoga experience. The remaining three (12%) participants commented on muscle soreness.
We have conducted a prospective study to evaluate yoga postures in pregnant women by assessing maternal and fetal status. Healthy pregnant women with a normal BMI in the third trimester were able to complete a single yoga session with no evidence of acute adverse maternal physiologic or fetal heart rate changes. Postures that have been reported to be contraindicated in pregnancy were also studied.12,13 12,13 We found that Child's Pose, Corpse Pose, Downward Facing Dog, and Happy Baby were not associated with acute adverse maternal or fetal responses.
All of the participants' vital signs and pulse oximetry were normal and no session was terminated for evidence of maternal distress. The presession systolic BP and the postsession diastolic BP showed a statistical significance among groups. However, this was not clinically significant. The fetal heart rate remained normal in all participants and in all postures. From this study, we conclude none of the 26 yoga postures had a negative acute effect on maternal or fetal status.
There were no falls or injuries. Modifications used included a chair, block, or wall. In balancing postures such as Warrior III, Tree Pose, Eagle Pose, and Half Moon Pose, a chair or wall was used. A block was used to aid in alignment and balance with postures such as Extended Side Angle Pose, Extended Triangle Pose, and Garland Pose. We recommend that these modifications be used by women in their third trimester to avoid falls and possible injuries.
This study has several strengths. Most exercise studies evaluate maternal and fetal well-being at the completion of the session. We were able to monitor maternal and fetal measurements continuously throughout the study. Our assessments were of objectively measured parameters. All women were positioned in the same postures, in the same order, in the same time interval, using the same modifications, and were all able to complete the yoga sequence. No participants were lost to follow-up 24 hours after the study.
There are some limitations to our study. Our population was small, uniform, and the participants were self-selected. Our session imperfectly mimicked an actual yoga class because postures were held longer to allow for monitoring and data collection. However, even a longer time for a posture did not create any concern for the maternal and fetal status, which actually strengthens our study. Although we strove to alternate between challenging and restorative postures, the pattern of repeating postures typically found in a yoga class was not studied. The average BMI in our study population was only 23.3, which does not represent the general pregnancy population, of whom more than half are overweight or obese.18 Data were not collected on amniotic fluid index, biophysical profile, or uterine artery Dopplers. We did not follow participants past 24 hours.
In conclusion, yoga was well tolerated with no acute adverse changes in maternal and fetal well-being. Child's Pose, Corpse Pose, Downward Facing Dog, and Happy Baby were completed without adverse changes in our study cohort.
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