Effects of Prenatal Yoga – How to Assess?

What are the effects of yoga on pregnancy and birth outcomes?

For more than 30 years, DTP has included exercise components that are elements of yoga (centering, deep breathing, mindfulness/transcendence, isometrics and relaxation) because these are measurable, effective components within a total fitness package.  Cardiovascular conditioning is our centerpiece – along with specific strength work – since these produce most of the benefits of prenatal fitness. Due to the growing popularity of prenatal yoga at the expense of cardiovascular conditioning and strength training, we have been seeking credible research evidence about yoga’s effect on pregnancy, birth and recovery.

Despite the length of time it has been available, there is little data to establish yoga’s efficacy beyond reducing some discomforts and perhaps improving body trust, often through the use of positions, breathing skills and mindfulness that are also common childbirth preparation and comfort measures. The relaxation element – achievable through any standard alpha brain wave producing method – can help promote progress in early labor, as the Relaxation Response (per Benson) is known to help the body release oxytocin in early labor (per Odent). However, the only study of the correlation among labor onset, yoga and the length of the first stage was very small. It was performed in Thailand and we cannot find any record of exactly what was performed during the six sessions over the course of pregnancy.

Yoga during pregnancy: effects on maternal comfort, labor pain and birth outcomes. Chuntharapat S, et al. Complement Ther Clin Pract. 2008 May;14(2):105-15. Epub 2008 Mar 4.

This study examined the effects of a yoga program on maternal comfort, labor pain, and birth outcomes. 74-primigravid Thai women were randomized. The yoga program involved six, 1-h sessions at prescribed weeks of gestation. A variety of instruments were used to assess maternal comfort, labor pain and birth outcomes. The experimental group was found to have a shorter duration of the first stage of labor. No differences were found, between the groups, regarding pethidine usage, labor augmentation or newborn Apgar scores at 1 and 5 min.

We also found a small, non-randomized study that indicated chronic practice of yoga produces similar affects.

Effects of a prenatal yoga programme on the discomforts of pregnancy and maternal childbirth self-efficacy in Taiwan. Sun YC, et al. Midwifery. 2010 Dec;26(6):e31-6. Epub 2009 Feb 25.

This non-randomized study aimed to provide yoga to primigravidas in the third trimester of pregnancy to decrease discomforts associated with pregnancy and increase childbirth self-efficacy. Low risk, sedentary primigravidas were targeted. The program was 12-14 weeks, with at least three sessions per week. Each workout lasted for 30 minutes. Program participants reported significantly fewer pregnancy discomforts than the control group (38.28 vs 43.26, z=-2.58, p=0.01) at 38-40 weeks of gestation and exhibited higher outcome and self-efficacy expectancies during the active stage of labour (104.13 vs 83.53, t=3.24, p=0.002; 99.26 vs 77.70, t=3.99, p ≤ 0.001) and the second stage of labour (113.33 vs 88.42, t=3.33, p=0.002; 102.19 vs 79.40, t=3.71, p ≤ 0.001) compared with the control group. Interestingly, the researchers concluded that the provision of booklets and videos on yoga during pregnancy may contribute to a reduction in pregnancy discomforts and improved childbirth self-efficacy.

Efficacy of yoga on pregnancy outcome. Narendran S, et al.  J Altern Complement Med. 2005 Apr;11(2):237-44.

The only matched-control study we have seen that reports any beneficial outcomes for yoga participants vs. controls was a small study conducted in India. Women participated daily in supervised 1-hour sessions, while controls walked. The daily yoga participants’ outcomes were improved compared with controls, including a reduction in IUGR, in conjunction with infection and PIH. It is important to keep in mind that these outcomes occurred in a setting where under-weight, over-work and infection-related complications are common.

It is interesting to note that aerobic fitness provides the same benefits as those seen in these studies, while also reducing the need for augmentation or other interventions, as well as reducing the risk of fetal distress.

During the second stage of labor, the transition to an ergotropic reflex promotes the release of oxytocin as the body changes from a parasympathetic state in the first stage to a sympathetic state in the second stage (that is why we call the end of the first stage transition). The physiology of pushing requires a very aggressive approach. Our in-house data suggest that we have found a balance for helping women develop the necessary traits to accomplish both the passive state required by the first stage and the endurance capacity to become aggressive during expulsion. We measure this in the reduction of our cesarean rate by 1/2 to 1/3 compared to the local population.

There is evidence of inverse risk for cesarean as the amount and intensity of aerobic conditioning increases. These studies are also fairly small, although they are numerous and have produced consistent results concerning dose-effect. There is growing interest within the health care field that supporting prenatal aerobics could help reduce the cesarean rate. There is no information from any credible sources concerning the relationship of yoga to type of birth. The only available statistical information is the coincidental correlation that as the cesarean rate has risen in the U.S., so has the population that participates in prenatal yoga.

Yoga remains an illusive subject of study. So much depends on who is teaching and what they are teaching. Unlike aerobics, strength, range of motion, relaxation response, balance, coordination and training specificity – all of which we can prescribe and measure – the popular term yoga has lost meaning. How much of exactly what is necessary to produce effects? What are those effects? Are they beneficial? These questions are yet to be answered.

2 Responses

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