EFFECTS OF ACUTE AND CHRONIC MATERNAL EXERCISE ON FETAL HEART-RATE

Maternal-fetal effects of cycle ergometer conditioning (heart rate of 145 beats/min at 25 min/day for 3 days/wk) were studied during the sec ond and third pregnancy trimesters. Subjects were 22 previously sedent ary women and 16 nonexercising pregnant control women. Fetal heart rat e (FHR) characteristics were studied before, during, and after 15 min of upright cycling at a maternal heart rate target of 145 beats/min at the end of both the second and third trimesters. Despite higher cycli ng power outputs in the exercised group, mean FHR responses were simil ar in both groups and conformed to 1) gradual increase in FHR baseline during exercise, 2) normal variability, and 3) normal reactivity. Fet al bradycardia was observed during (n = 1) and after (n = 2) exercise in three isolated tests. The timing of these events suggested that the likelihood of significant fetal hypoxia is highest in the immediate p ostexercise period. These results also support the hypothesis that phy sically conditioned women can perform at higher exercise power outputs than sedentary women without inducing fetal hypoxic stress. Further s tudy is recommended to examine possible fetal and placental adaptation s to maternal aerobic conditioning.