Research
Obstetrics
Physical exercise during pregnancy and fetal growth measures: a study within the Danish National Birth Cohort

Presented at the 18th World Congress of Epidemiology, Porto Alegre, Brazil, Sept. 20-24, 2008, and the National Day of Midwifery Research, Copenhagen, Denmark, Oct. 3, 2008.
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Objective

The objective of the study was to examine the association between physical exercise during pregnancy and fetal growth measures.

Study Design

Data on 79,692 liveborn singletons from the Danish National Birth Cohort were collected between 1996 and 2002. Mean differences in birthweight, length, ponderal index, head and abdominal circumference, and placental weight and hazard ratios of small- and large-for-gestational-age babies were calculated.

Results

Our data indicated smaller babies in exercising women compared with nonexercisers, but the differences were small, and only a few were statistically significant. Exercising women had a slightly decreased risk of having a child small for gestational age (hazard ratio, 0.87; 95% confidence interval, 0.83–0.92) and large for gestational age (hazard ratio, 0.93; 95% confidence interval, 0.89–0.98).

Conclusion

The findings do not indicate sizable effects on fetal growth measures related to exercise apart from a modest decreased risk of small- and large-for-gestational-age infants. These findings do not speak against advising pregnant women to be physically active during pregnancy.

Section snippets

Materials and Methods

The Danish National Birth Cohort Study (DNBC) is a cohort of a little more than 100,000 pregnancies with written informed consents from the mothers. The initial data collection included telephone interviews, questionnaires, and blood samples and took place between 1996 and 2002.

For this study, we used data from 2 pregnancy interviews carried out at approximately 16 and 31 completed weeks of gestation. More details about the cohort are presented elsewhere.45 Some of the women provided data on

Results

Table 1 shows some characteristics of the women according to exercise, mean birthweight, SGA, and LGA. In 37% of 79,692 pregnancies, the mother engaged in leisure time physical activity at the time of the first pregnancy interview. This proportion decreased to 31% at the time of the second pregnancy interview. Compared with active women, nonexercisers had lower sociooccupational status; were more often parous, overweight, or obese; and were more likely to smoke 10 cigarettes per day or more.

Comment

Overall, this study did not indicate a strong negative effect of leisure-time physical exercise during pregnancy on fetal growth measures recorded at birth. There was a tendency toward smaller size of offspring with exercise and some of the trend tests performed were statistically significant, but the differences are probably too small to cause concern. The results may indicate that the offspring of smoking mothers benefit more from exercise than nonsmokers, although this finding needs to be

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  • Cited by (0)

    Cite this article as: Juhl M, Olsen J, Andersen PK, et al. Physical exercise during pregnancy and fetal growth measures: a study within the Danish National Birth Cohort. Am J Obstet Gynecol 2010;202:63.e1-8.

    The Danish National Research Foundation established the Danish Epidemiology Science Centre, which initiated and created the Danish National Birth Cohort. The cohort is a result of a major Grant from this foundation. Additional support for the Danish National Birth Cohort is obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, and the Augustinus Foundation. This specific study was supported by Grants from the Danish Medical Research Council, the Augustinus Foundation, the Danish Midwifery Association, the Danish Graduate School in Public Health Sciences, and the Danish National Board of Health. None of the funders were involved in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, or approval of the article.

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