Article Abstract:
It should be likely that regular physical activity and the resulting physical fitness would benefit the course and outcome of pregnancy, including birth weight. However, studies of this possible association have had conflicting conclusions, presumably due to the confounding effects of maternal, uterine, fetal, and obstetric factors. To better evaluate the consequences of exercise on birth weight, infant size was evaluated following the full-term pregnancies of 77 runners and aerobic dancers and 55 women who exercised at similar levels before but not during pregnancy. The exercising women gained 6.4 pounds less than nonexercisers (mostly due to lower weight gains by runners), while dietary intake of the two groups was similar. Length, head circumference, and placental weight were similar among all infants, but infants born to exercisers were lower in birth weight, ponderal index (a ratio of height to weight), and ratio of fetal to placental weight. These changes are suggestive of soft tissue growth restriction, not involving the brain, which typically occurs in later pregnancy. These changes were more marked in infants born to runners than those born to aerobic dancers. Similarly, exercisers' infants had a small skin-fold thickness and a higher ratio of head circumference to abdominal circumference. Most of the differences in birth weight among the groups of infants were attributable to a lower amount of fatty tissue in exercisers' infants. The level of exercise performed by runners correlated significantly to their infants' birth weight. Placental weight and pregnancy weight gain were related to birth weight. The study indicates that intense exercise during pregnancy, in well conditioned women, is associated with a decrease in birth weight, primarily due to decreased fat mass. Further research is needed to improve understanding of the interplay between pregnancy and exercise. (Consumer Summary produced by Reliance Medical Information, Inc.)
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Article Abstract:
Fetal heart rate increases during and after maternal exercise, and the magnitude of the increase appears to rise with gestational age and the intensity and duration of exercise. Fetal heart rate was monitored in 120 healthy, physically active pregnant women before, during and after exercise. In all but 3% of the trials, FHR increased. The average overall increase was 15 beats per minute. Before the 26th week of pregnancy, FHR responses did not vary with type of exercise. After that, the FHR response to biking was significantly lower than that for other exercises such as running and swimming. At the same level of intensity, FHR increased an average of 10 beats per minute at 22.5 weeks and an average of 16 beats per minute at 29 weeks. At the same gestational age, FHR increased with exercise intensity. Also, FHR increased as the duration of exercise at the same intensity increased.
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Article Abstract:
Sustained exercise may increase blood levels of the female sex hormone 17beta-estradiol in female athletes. A study examined the effect of 20 minutes of sustained exercise on the blood levels of 17beta-estradiol and cortisol, another hormone, in 75 women between 27 and 38 years old with a regular menstrual cycle who had been running or doing aerobics routinely for six months. The women's blood levels of 17beta-estradiol consistently increased after periods of sustained exercise. The elevation in blood levels of 17beta-estradiol increased as the level of exercise intensity increased. Blood levels of cortisol were not affected significantly by periods of sustained exercise. The rise in blood levels of 17beta-estradiol can be used to measure the changes in blood flow to the liver during sustained exercise.
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