Too much exercise in early pregnancy may cause pre-eclampsia

Too much exercise in early pregnancy may cause pre-eclampsia
Danish and Norwegian researchers studied 85,139 pregnant women enrolled in the Danish National Birth Cohort (DNBC) between 1996 and 2002. Data collected included information about maternal BMI, whether women smoked, their demographic background and recorded cases of pre-eclampsia. This was compared against data about the amount of physical activity undertaken during pregnancy, measured as the amount of time in minutes spent each week exercising.

Physical activity was defined by researchers as specific forms of sport such as jogging, cycling, swimming, or ball and racket games. It did not include work-based physical activity. Each activity was categorised as vigorous, moderate or a mixture, depending on the rate of energy expenditure, measured in metabolic equivalents (METs).

Researchers found physical inactivity was more common in younger women, underweight or obese women, smokers, women who have had more than one child and those with lower socio-economic status. Women with high levels of physical activity (270 mins/week to 419 mins/week, and 420 mins per week or more) were associated with increased risks of severe pre-eclampsia (odds ratios 1.65 and 1.78 respectively compared with non-exercising women), although the absolute risks were still small (1.18% and 1.29% respectively). Moderate to low exercise levels (<270 mins/week) showed no association with severe pre-eclampsia. Cycling and brisk walking over long durations was also associated with an increased risk of severe pre-eclampsia. 75 - 269 mins/week of jogging was also associated with an increased risk (odds ratio 2.61). However, once again, the absolute level of risk was small (1.7%).

These findings are contrary to the researchers’ initial hypothesis that exercise may have a positive effect on the maternal body. Official guidance from the US, Denmark and Norway recommend that pregnant women should take at least 30 minutes of physical exercise each day. This has general benefits for health and did not appear to be associated with a pre-eclampsia risk (although neither did it appear to reduce risk). Studies on non-pregnant subjects have demonstrated how increased levels of exercise protect against hypertension and have an effect on lowering triglycerides, cytokines and insulin resistance (factors known to be higher in pre-eclamptic women). Researchers of the present study believe that a plausible biological explanation for their findings is that intense physical activity induces oxidative stress in the mother and this in turn contributes to the development of pre-eclampsia.

Senior author, Dr Sjurdur F. Olsen, from the Statens Serum Institut in Copenhagen, Denmark and Adjunct Professor of Nutrition at the Harvard School of Public Health in Boston, USA said “Recommendations have been issued in several countries that pregnant women should exercise at least 30 minutes each day. An important underlying contention is that this can reduce risk of pre-eclampsia. In our study, we were unable to substantiate that physical activity in early pregnancy has a protective effect against pre-eclampsia.

“Another unexpected finding was that leisure time exercise, in amounts that were only slightly higher than the recommended amount, seemed even to be associated with an increased risk of severe types of pre-eclampsia.

“Further research is needed in other large prospective cohort databases which are now emerging in several countries. Until that has happened, recommendations in the field should remain unchanged.”

Professor Philip Steer, BJOG editor-in-chief, said “Clinical guidelines in the UK stress that selective and moderate exercise during pregnancy can be beneficial. These include aerobic and strength-conditioning exercises. While general fitness is a good thing in many respects, these data suggest that it may be unwise to exercise to peak fitness levels.

“This new research is useful as it provides us with an indication of how much exercise pregnant women should take. As with everything in life, too much of a good thing can be bad for you, and moderation in all things remains a good policy.”

ENDS

Notes
BJOG: An International Journal of Obstetrics and Gynaecology is owned by the Royal College of Obstetricians and Gynaecologists (RCOG) but is editorially independent and published monthly by Wiley-Blackwell. The journal features original, peer-reviewed, high-quality medical research in all areas of obstetrics and gynaecology worldwide. Please quote ‘BJOG' or ‘BJOG: An International Journal of Obstetrics and Gynaecology' when referring to the journal.

This study was funded by the March of Dimes Birth Defects Foundation and the EU’s Early Nutrition Programming Project, EARNEST.

For further information, please contact the senior author of the paper, Dr Sjurdur F. Olsen, please call +4522289568 or email sfo@ssi.dk . To speak to Professor Philip Steer, please call +44 (0) 20 7772 6446 or email mailto:p.steer@imperial.ac.uk?Subject=Email%20from%20RCOG%20website.
Date published: 03/12/2008 - 01:00Published by: Simon KempNo of comments: 0
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BJOG press release Eclampsia