Regular Exercise During Pregnancy May Lower Risk for Excessive Birth Weight

From Medscape Medical News
Laurie Barclay, MD

September 23, 2009 —- Regular exercise during pregnancy may lower the risk for excessive birth weight, according to the results of a cohort study reported in the October issue of Obstetrics & Gynecology.

"Despite extensive literature on the relationship between regular exercise during pregnancy and mean birth weight, the results are ambiguous and lack consistency," write Katrine Mari Owe, MSci, from Norwegian School of Sport Sciences in Oslo, Norway, and colleagues. "Both a positive and negative association with newborn birth weight have been suggested....The aim of the present study was to estimate, in a prospective cohort of pregnant women, the association of regular exercise, performed before and during pregnancy, with excessive newborn birth weight."

This analysis included data from 36,869 singleton pregnancies lasting at least 37 weeks among participants in the Norwegian Mother and Child Cohort Study. Two questionnaires administered during pregnancy weeks 17 and 30 provided data on regular exercise, and linkage to the Medical Birth Registry of Norway provided information regarding newborn birth weight. Excessive newborn birth weight, defined as birth weight at or above the 90th percentile, was the primary endpoint of the study. Associations were estimated separately for nulliparous (n = 16,064) and multiparous (n = 20,805) women with use of logistic regression analyses.

Of 4033 newborns (10.9%) with excessive birth weight, 2263 (56.1%) were born to multiparous women. Regular exercise (at least 3 times per week) in pregnancy weeks 17 and 30 was inversely associated with excessive newborn birth weight in nulliparous women (adjusted odds ratio [aOR], 0.72; 95% confidence interval [CI], 0.56 - 0.93 and aOR, 0.77; 95% CI 0.61 - 0.96, respectively).

"Regular exercise performed before pregnancy did not affect the probability of delivering newborns with an excessive birth weight in nulliparous or multiparous women," the study authors write.
"Regular exercise during pregnancy reduces the odds of giving birth to newborns with excessive birth weight by 23–28%."

Limitations of this study include indirect assessment of regular exercise with use of self-administered questionnaires, low response rate in the Norwegian Mother and Child Cohort Study, and possible confounding factors.

"Although our results indicate a protective effect of regular exercise during pregnancy, there seems to be an urgent need for randomized controlled trials with high methodological and interventional quality to be carried out to study the causal relationship between regular exercise in pregnancy and excessive newborn birth weight," the study authors conclude.

The Norwegian Mother and Child Cohort Study is supported by the Norwegian Ministry of Health, National Institutes of Health/National Institute of Environmental Health Sciences, National Institutes of Health/National Institute of Neurological Disorders and Stroke, and the Norwegian Research Council/Functional Genomics Project (FUGE). The study authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2009;114:770-776.