Should pregnant women stop exercising?

by Renee Jefferys MSc., Dr. Karen Nordahl MD

For those of us with an interest in antenatal fitness, as well as a physician who practices obstetrics, the recent article in the November 2007 British Journal of Obstetrics and Gynecology has started some lively discussion.

To summarize the article (the reference is below) Madsen et all performed phone interviews with over 92 000 pregnant women, inquiring about their leisure time physical activities in pregnancy.1

The conclusion drawn from the study was that "the study suggested that exercise early in pregnancy is associated with an increase risk of miscarriage".1 The authors also went on to state that the results should be interpreted with caution, as the study was retrospective and there was a possibility of recall bias.

How the scientific method works

When one looks at any single research article for an answer one misses the bigger picture...we very seldom change how we do things in medicine based on one study (unless the results are VERY strong ). Scientists rarely make broad statements about recommendations based on many, many studies, and never based on one single study. This is especially true when you are looking at complex systems. Pregnancy is a complicated physiological process with many variables; therefore one study cannot answer the entire picture.

Problems with extrapolating the data from this article, specifically.

Although this research and article are well done, there are several problems that exist and that the authors themselves point out.1

First, this is a case-control/retrospective study. A study like this is often done because it is not cost effective/ethical to do better blinded-randomized controlled trials. ( A pregnant women would definitely know if she was in the 'exercising group') This study design is not without problems. First, if a women has a miscarriage, her perspective on all her activities that may have been related is skewed, for example, she would like something tangible to be the cause of the terrible event, and may over report her physical activities This is called 'recall bias' and is mentioned by the study authors as a potential problem with their data . 1

Second, this study did not control for prior exercise levels; from this study we are unable to determine the impact of pre-pregnancy activity levels. Is the resulting increase in miscarriage rate due to an increase or decrease in normal activity levels.

Finally as we extrapolate to other populations, is this Danish population the same as the United Kingdom or the United States? Since the answer is no, then there may be causes, not studied, that influence the miscarriage rate in this population.

Review of the Research

Besides this article there are other articles that have tried to answer the question about wether or not exercise during pregnancy is safe and how it should be done.

Clapp et al 2,3 have published numerous articles looking at the safety and efficacy of exercise and pregnancy. The conclusions have been consistently that exercise is safe and beneficial to the pregnant women. The limitations of his studies, however, are that most of the subjects are highly active, 5-7 days a week of moderate to vigours activity, 30-60 minutes and all subjects were required to maintain their activity level at a predefined level throughout their pregnancy. Admittedly it is easy to do when you are in a controlled research study with a qualified exercise physiologist looking over weekly sessions, not as easy when you are going it alone. Can his data be applied equally to all other pregnant women? The answer is yes to most of it; however data on shortening delivery may only apply to the women in the study.

What about the benfits to exercise and pregnancy other than health. The study by Wallace et al.4 looked at what happens when exercise patterns change (increases or decreases), as do with most pregnant women, in real life. This study found exercise to be helpful in managing the common discomforts of pregnancy, with discomforts going down as exercise goes up.

What about more specific types of exercise? Jeffreys et al. 5 address the question of supine exercise. In the study, women were asked to do sit up type exercises, in late pregnancy, and the blood flow to the uterus was measured. The result, blood flow did not decrease. So can we say exercise on your back after the 4th mounth is safe, NO, not yet. The study will need to be reproduced, done in less fit populations, and at other pregnancy time points before we begin to change the accepted guidelines.

So what do we do? First acknowledge that the study exists as does a large volume of other research on exercise and pregnancy. All conclusions, for and against exercise during pregnancy, need to be based on the entire research available, not one single article. Before you make recommendations to your pregnant clients, make sure you are familiar with all the research. Remember, that exercise during pregnancy has been demonstrated to be safe in low risk pregnancies (American College of Obstetricians and Gynecologists 2004).

Since we don't treat 90,000 women on a regular basis or over a lifetime, we need to remember this about research. "Statisticians are more accurate on average than physicians, in diagnosing disease, however physicians are more accurate for the individual" (CRBuncher, University of Cincinnati); and therefore each pregnant woman needs to talk to her personal physician and make a decision that is right for her as an individual not as a statistic in a research study.

Renee Jefferys MSc. And Dr karen Nordahl MD are co creators of the Fit to Deliver pre and post natal programme. Renee is an exercise physiologist and personal trainer working in Cincinnati, Ohio. Karen is a medical doctor who practices family medicine and obstetrics at BC Women's hospital in Vancouver. They will be presenting the Fit to Deliver training programme on 10-11th May 2008, London UK. For more information contact info@body-a-wake.com or call 07929391942

Reference:

1 Madsen M, Jorgensen T, Jensen M, Juhl M, Olsen J, Andersen P, Nybo Andersen A. Leisure time physical exercise during pregnancy and the risk of miscarriage: a study within the Danish National Birth Cohort. BJOG 2007;114: 1419-1426

2 Clapp, JF,3rd, Little, KD. The interaction between regular exercise and selected aspects of women's health. Am J Obstst Gynecol. 1995 Jul;173(1):2-9.

3. Clapp JF 3rd, Exercise during pregnancy. A clinical update. Clin Sports Med. 2000 Apr;19(2):273-86.

4. Wallace AM, Boyer DB, Dan A. Holm K. Aerobic exercise, maternal self-esteem, and physical discomforts during pregnancy. J Nurse Midwifery. 1986 Nov-Dec;31(6):255-62.

5. Jeffreys, RM. Stepanchak W. Lopex B, Hardis J, ClappJF 3rd. Uterine blood flow during supine rest and exercise after 28 weeks of gestation. BJOG. 2006 Nov;113(11):1239-47..