The course of labor after endurance exercise during pregnancy James F. Clapp III, MD Burlington, Vermont This study was designed to test the hypothesis that continuation of a regular running or aerobics program, or both, during the latter half of pregnancy would have a negative effect on the course and outcome of labor. The onset, course, and outcome of labor were independently monitored in 131 well-conditioned recreational athletes who had an uneventful first half of pregnancy. Daily exercise performance was quantitated before conception and throughout pregnancy. Comparisons were made between the 87 women who continued to exercise regularly at or above 50% of their preconceptional level throughout pregnancy and the 44 who discontinued their regular exercise regimen before the end of the first trimester. The incidence of preterm labor was similar in the two groups (9%). Labor began significantly earlier in the exercise group (277 ± 6 vs 282 ± 6 days). The women who continued to exercise had a lower incidence of abdominal (6% vs 30%) and vaginal (6% vs 20%) operative delivery, and active labor was shorter (264 ± 149 vs 382 ± 275 min) in those who were delivered vaginally. Finally, clinical evidence of acute fetal stress (meconium, fetal heart pattern, and Apgar score) was less frequent in the exercise group (50% vs 26%), although birth weight was reduced (3369 ± 318 vs 3776 ± 401 gm). These data negate the initial hypothesis and indicate that, in well-conditioned women who regularly perform aerobics or run, continuation of these exercise regimens has a beneficial effect on the course and outcome of labor. (AM J OBSTET GVNECOL 1990;163:1799-805.)
Key words: Exercise, pregnancy, labor
It is likely that regular physical activity, as well as the improved physical fitness that accompanies it, has a beneficial effect on the course and outcome of labor. However, a direct assessment of this relationship is diffIcult because of the confounding effects of the multiple exercise variables involved and the other maternal, uterine, fetal, and obstetric factors that are known to influence labor. Thus it is not surprising that the reports dealing with the impact of exercise during pregnancy on labor have been divergent with 'some reporting benefit" 2 and others either no effect'-6 or a detrimental one. 7 ,8 The purpose of this study was to provide a definitive answer to the question, does continuation of a regular exercise regimen throughout pregnancy influence the course and outcome of labor? In an attempt to control the multiple variables involved, the current study used a prospective design and was limited to wellconditioned recreational athletes who performed one of two forms of high-intensity exercise (running or aerobics) in which a large fraction of the body's muscle mass is used against gravity for relatively prolonged From the Department of Obstetrics and Gynecology, The University of Vermont College of Medicine, Supported in part by National Institutes of Health grant HD21268 and grant 6-464 from the March of Dimes Birth Defects Foundation, Presented at the Thirty-seventh Annual Meeting of the Society for Gynecologic Investigation, St, Louis, Missouri, March 21-24, 1990. Reprint requests: James F, Clapp III, MD, Physiology Laboratory, Department of Obstetrics and Gynecology MetroHealth Medical Center, 3395 Scranton Road,. Cleveland, OH 44109,
6/6/24724
periods of time. The experimental design also included a relatively large sample size, a matched populace of recreational athletes who discontinued exercise, daily monitoring of exercise performance before and during pregnancy, and on-site, independent monitoring of the course and outcome of labor. The hypothesis tested was that when a regular running or aerobics regimen is continued at or above 50% of preconceptional level> throughout pregnancy it has a negative impact on the course and outcome of labor. The objective outcome parameters included indices of labor onset, management, course, complications, outcome, and fetal stress. Material and methods
Between July 1983 and February 1990, we prospectively monitored the spontaneous exercise performance of 67 recreational runners and 64 aerobic dancers who, with the exception of preterm labor, had clinically normal pregnancies, with labor and delivery under surveillance by study personnel. All subjects had been exercising regularly for at least 6 months before conception, three or more times each week for at least 30 minutes each session at an intensity >50% of their individual maximum capacity. Written informed consent was obtained from each subject at the time of ellrollment. Because of very real human subject concerns and an unwillingness on the part of many subjects to change their specific exercise regimen, the subjects were not randomized prospectively to different regimens. Rather, they were divided into two groups on the basis of their spontaneous level of exercise perfor1799
December 1990
1800 Clapp
mance during pregnancy. The 46 runners and 41 aerobic dancers who continued to exercise at or above 50% of their preconceptional performance level throughout the 10 lunar months of pregnancy formed the continued exercise group. The 21 runners and 23 aerobic dancers who spontaneously stopped their regular exercise regimen by the end of the first trimester formed the discontinued exercise or reference group. To quantitate each individual's exercise, we measured maximum oxygen consumption before conception and the relationship between heart rate and oxygen consumption during graded exercise in the laboratory before conception and every 6 to 8 weeks during pregnancy. Concurrent field heart rate data and the time spent in exercise were gathered with a portable telemetry system, and the data were used to calculate overall weekly exercise performance. This was quantitated by means of the training effect method and was expressed as a duration-intensity index (product of weekly duration and average weekly intensity).9 Pregnancy was confirmed within a few days of missed menses (~-human chorionic gonadotropin level) and dates were confirmed by early ultrasonography 53 to 60 days after the last menstrual period. With the exception of preterm labor, the pregnancies were all clinically normal and the course and outcome of each labor were monitored by an independent observer who was present but was not involved in the subject's clinical care. The onset of labor was defined as the onset of regular uterine contractions followed by progressive cervical change. Preterm labor was defined as the onset of labor before 263 days' gestation «37V2 weeks of gestation completed), and premature rupture of the membranes was defined as the onset of persistent vaginal fluid leakage before the onset of subjective uterine activity that was confirmed on examination by an alkaline pH and ferning of the fluid. The start of the active phase of labor was set at 4 cm of cervical dilation with regular uterine contractions, and women who were further advanced in labor at the time of initial evaluation were not included in the study. An abnormal fetal heart pattern was defined as one that initiated medical intervention and the Apgar score was assigned by the delivery room nurse or pediatrician in attendance. Significant between-group differences for normally distributed parameters were detected with the unpaired Student t test. Differences in exercise performance were assessed with the Wilcoxon-MannWhitney test. Between- and within-group differences in incidence were detected by means of the X2 statistic with the Yates correction for small groups. Regression analysis was used to detect any within-group effect of weight gain, exercise performance, preconceptional weight, and parity on numeric parameters. Significance was set at the 0.05 level.
Am
J Obstet Gynecol
Results
Maternal characteristics. The subjects were all white, were middle or upper socioeconomic class, and worked part-time or full-time. None smoked, alcohol intake was limited (maximum recorded was four glasses of beer per week), and all subjects ate an adequate caloric, wellbalanced diet that was low in simple sugar and high in complex carbohydrate. They were all in excellent health and averaged 31 years of age (range 24 to 38). Preconceptional weight and height ranged between 42.3 and 78.4 kg and between 155 and 185 em, respectively. Most (128/131) had a normal menstrual pattern; 52% of the populace were nulliparous and 47% were primiparous. Two subjects were secundiparous. The only obstetric risk factors included one subject with a history of diethylstilbestrol exposure, two with a history of bulimia in college, and one with a prior preterm delivery. Data on family obstetric history were not obtained, but there were no between-group differences in the distribution of birth orders, birth weights, or route of delivery of the subjects themselves. All subjects were fit as assessed by preconceptional morning pulse rate (range 48 to 62 beats/min), maximal oxygen consumption (range 43 to 68 mllkg/min), weight for height (range of ponderal index 1.06 to 1.38), and percent body fat (range 10% to 24%). When referenced to current normative standards,1O all subjects had maximum oxygen consumptions in the upper 15% of the overall populace with an average of 54.3 mllkg/min. There were no significance between-group differences in any of these demographic, morphometric, lifestyle, and obstetric variables or in the four objective indices of fitness. In fact, the only two discernible between-group differences were that the women who discontinued their regular exercise regimen in early pregnancy had an overall level of exercise performance before conception that averaged 25% less than that of the women who continued their regular regimen throughout pregnancy (Table I) and their average pregnancy weight gain (17.2 kg) was 3.6 kg greater than that of those who continued exercise (13.6 kg). Maternal exercise performance. Before conception running performance ranged between 14 and 68 km each week at a pace between 3.9 and 6.1 min/km and an intensity ranging between 51 % and 83% of maximum. Participation in aerobics ranged between 3 and ~"I 11 sessions each week at an intensity between 54% and 90% of maximum during the 25- to 30-minute highintensity phase of the workout. The mean group pulse rate was 166 beats/min during both aerobics and running, but there was a great deal of individual variation with individual average exercise pulse rates ranging between 122 and 190 beats/min. The relationship between pulse rate and exercise intensity was extremely variable such that a pulse rate of 140 beats/min for
Endurance exercise and labor
Volume 163 Number 6, Part I
1801
Table I. Maternal exercise performance Control
(N = 44)
Duration-intensity index before pregnancy During pregnancy* (%) Last half of pregnancy* (%) 9-10 mo of pregnancy* (%)
9840 :t 14:t 5 :t 2 :t
303 17 10 3
Exercise (N = 87)
13,070 68 65 60
:t :t :t :t
332 16 17 18
Significance
0.01 0.01 0.01 0.01
Values are mean :t SD. *Percent of prep regnancy value.
different individuals represented an oxygen consumption that ranged between 42% and 73% of measured maximum capacity. During the first half of pregnancy the intensity of exercise was maintained at or near preconceptional levels (51 % to 90% of maximum) in the continued exercise group. However there was an average decrease in running distance and number of a_ez.:obics classes to 29 km/wk and 4.8 classes per week, resulting in a 23% average reduction in the time spent in exercise during the first half of pregnancy. The relationship between exercise intensity and pulse rate became more variable. At 8 and 16 weeks a pulse rate of 140 beats/min for different individuals represented an oxygen consumption that ranged between 31 % and 76% of preconceptional maximum capacity. During the latter half of pregnancy the range of intensity decreased to 50% to 76% of maximum capacity, but the range of the time spent in exercise increased (40% to 160% of preconceptional duration). As a result the average running distance and overall aerobics effort remained stable. Again there was wide individual variation in both pulse rate and its relationship to exercise intensity. Individual average pulse rates during exercise ranged between 110 and 187 beats/min, and a rate of 140 beats/min for different individuals represented an oxygen consumption that ranged between 35% and 68% of preconceptional measured maximum capacity. Thus during pregnancy the slope of the relationship between individual pulse rate and exercise intensity, measured as a percentage of preconceptional maximum absolute oxygen consumption, changed in different directions at different time points in pregnancy, and individual average pulse rates, which ranged between 110 and 195 during exercise in pregnancy, were not by themselves an accurate index of individual exercise intensity. The individual range of overall exercise performance for the entire pregnancy ranged between 50% and 109% of preconceptional levels. For the latter half of pregnancy the range in individual overall performance was 50% to 122% of preconceptional levels. Mean values for the entire group are listed in Table I for the entire pregnancy, the last 5 months, and last 2 months. Although the women who discontinued regular exercise had an overall preconceptional performance
level that averaged 25% less than that of those who continued, their overall level of performance still represented an average of 26 km/week for the runners and an average of four or five classes per week for those who performed aerobics at similar intensities. The majority of these women (n = 37) spontaneously discontinued exercise in early pregnancy for one of two reasons. First, dealing with the extreme fatigue and nausea of early pregnancy completely abolished their desire to exercise early on, and they simply never prioritized the time to begin their regular exercise regimen again during pregnancy. Second, they could not cope emotionally with the reduction in performance level suggested by their physicians or their own uncertainties concerning the potential impact of the exercise on the pregnancy, which were reinforced at the initial prenatal visit. As a result they simply stopped until after delivery. In the remainder minor injury, job pressures, or paternal concerns played a major role. As a group (Table I) their average level of overall performance fell to 2% to 5% of preconceptionallevels by the end of the fifth lunar month. Onset of labor. As detailed in Table II, continuing the ballistic motion associated with running and aerobics throughout pregnancy did not increase the incidence of either the onset of labor before 37V2 weeks of gestation were completed or membrane rupture before the onset of perceived labor. The incidence of spontaneous membrane rupture that eventually necessitated induction of labor was also similar in the two groups. However, the onset of labor at or near term occurred 5 days earlier on average in the women who continued exercise. When examined individually within groups, prepregnancy weight, pregnancy weight gain, parity, preconceptional or pregnant level of exercise performance, and exercise type (aerobics or running) did not have a significant effect on gestational length (all individual R2 values 4000 gm was associated with an increased incidence of protraction disorders and operative delivery. Within the exercise-continued group there was no detectable relationship between birth weight and obstetric intervention with birth weight cutoffs of 3500 and 3750 gm (only one infant weighed >4000 gm). Within the overall populace there was a significant relationship (r 2 = 0.2768) between birth weight and pregnancy weight gain. As discussed elsewhere, 11 this correlation is due to the independent effects of exercise on both parameters.
Comment These data negate the initial hypothesis and clearly indicate that, in physically fit women who performed aerobics or ran on a regular basis before pregnancy, continuing a regular running or aerobics exercise program above a maintenance level throughout pregnancy had a beneficial effect on multiple aspects of the course and outcome of labor. Overall, continued exercise was
Endurance exercise and labor
Volume 163 Number 6, Part 1
1803
Table IV. Management-Vaginal deliveries only Control
Parameter
Exercise
(N = 31)
382 ± 302 ± 52% (n 29% (n
Active labor (min) (mean ± SD) Active first stage (min) (mean ± SD) Parous Forceps use Episiotomy done Epidural anesthetic use Abnormal labor pattern
275 191 = 16)
Significance
264 ± 149 223 ± 134 53% (n = 43)
0.01 0.01 NS 0.01 0.01 0.01 0.01
6% (n = 46% (n = 29% (n = 20% (n =
= 9) 81% (n = 25) 41% (n = 13) 35% (n = II)
Actual number of cases is shown in parentheses. Active labor, 4 em dilatation
(N = 82)
to
5)
38) 24) 16)
delivery.
Active first stage, 4 to' 10 em dilatation.
Table V. Fetal condition and outcome Parameter
Control (N = 44)
Exercise (N = 87)
Significance
Meconium in fluid Abnormal heart rate* Nuchal cord 1 min Apgar score
Key words: Exercise, pregnancy, labor
It is likely that regular physical activity, as well as the improved physical fitness that accompanies it, has a beneficial effect on the course and outcome of labor. However, a direct assessment of this relationship is diffIcult because of the confounding effects of the multiple exercise variables involved and the other maternal, uterine, fetal, and obstetric factors that are known to influence labor. Thus it is not surprising that the reports dealing with the impact of exercise during pregnancy on labor have been divergent with 'some reporting benefit" 2 and others either no effect'-6 or a detrimental one. 7 ,8 The purpose of this study was to provide a definitive answer to the question, does continuation of a regular exercise regimen throughout pregnancy influence the course and outcome of labor? In an attempt to control the multiple variables involved, the current study used a prospective design and was limited to wellconditioned recreational athletes who performed one of two forms of high-intensity exercise (running or aerobics) in which a large fraction of the body's muscle mass is used against gravity for relatively prolonged From the Department of Obstetrics and Gynecology, The University of Vermont College of Medicine, Supported in part by National Institutes of Health grant HD21268 and grant 6-464 from the March of Dimes Birth Defects Foundation, Presented at the Thirty-seventh Annual Meeting of the Society for Gynecologic Investigation, St, Louis, Missouri, March 21-24, 1990. Reprint requests: James F, Clapp III, MD, Physiology Laboratory, Department of Obstetrics and Gynecology MetroHealth Medical Center, 3395 Scranton Road,. Cleveland, OH 44109,
6/6/24724
periods of time. The experimental design also included a relatively large sample size, a matched populace of recreational athletes who discontinued exercise, daily monitoring of exercise performance before and during pregnancy, and on-site, independent monitoring of the course and outcome of labor. The hypothesis tested was that when a regular running or aerobics regimen is continued at or above 50% of preconceptional level> throughout pregnancy it has a negative impact on the course and outcome of labor. The objective outcome parameters included indices of labor onset, management, course, complications, outcome, and fetal stress. Material and methods
Between July 1983 and February 1990, we prospectively monitored the spontaneous exercise performance of 67 recreational runners and 64 aerobic dancers who, with the exception of preterm labor, had clinically normal pregnancies, with labor and delivery under surveillance by study personnel. All subjects had been exercising regularly for at least 6 months before conception, three or more times each week for at least 30 minutes each session at an intensity >50% of their individual maximum capacity. Written informed consent was obtained from each subject at the time of ellrollment. Because of very real human subject concerns and an unwillingness on the part of many subjects to change their specific exercise regimen, the subjects were not randomized prospectively to different regimens. Rather, they were divided into two groups on the basis of their spontaneous level of exercise perfor1799
December 1990
1800 Clapp
mance during pregnancy. The 46 runners and 41 aerobic dancers who continued to exercise at or above 50% of their preconceptional performance level throughout the 10 lunar months of pregnancy formed the continued exercise group. The 21 runners and 23 aerobic dancers who spontaneously stopped their regular exercise regimen by the end of the first trimester formed the discontinued exercise or reference group. To quantitate each individual's exercise, we measured maximum oxygen consumption before conception and the relationship between heart rate and oxygen consumption during graded exercise in the laboratory before conception and every 6 to 8 weeks during pregnancy. Concurrent field heart rate data and the time spent in exercise were gathered with a portable telemetry system, and the data were used to calculate overall weekly exercise performance. This was quantitated by means of the training effect method and was expressed as a duration-intensity index (product of weekly duration and average weekly intensity).9 Pregnancy was confirmed within a few days of missed menses (~-human chorionic gonadotropin level) and dates were confirmed by early ultrasonography 53 to 60 days after the last menstrual period. With the exception of preterm labor, the pregnancies were all clinically normal and the course and outcome of each labor were monitored by an independent observer who was present but was not involved in the subject's clinical care. The onset of labor was defined as the onset of regular uterine contractions followed by progressive cervical change. Preterm labor was defined as the onset of labor before 263 days' gestation «37V2 weeks of gestation completed), and premature rupture of the membranes was defined as the onset of persistent vaginal fluid leakage before the onset of subjective uterine activity that was confirmed on examination by an alkaline pH and ferning of the fluid. The start of the active phase of labor was set at 4 cm of cervical dilation with regular uterine contractions, and women who were further advanced in labor at the time of initial evaluation were not included in the study. An abnormal fetal heart pattern was defined as one that initiated medical intervention and the Apgar score was assigned by the delivery room nurse or pediatrician in attendance. Significant between-group differences for normally distributed parameters were detected with the unpaired Student t test. Differences in exercise performance were assessed with the Wilcoxon-MannWhitney test. Between- and within-group differences in incidence were detected by means of the X2 statistic with the Yates correction for small groups. Regression analysis was used to detect any within-group effect of weight gain, exercise performance, preconceptional weight, and parity on numeric parameters. Significance was set at the 0.05 level.
Am
J Obstet Gynecol
Results
Maternal characteristics. The subjects were all white, were middle or upper socioeconomic class, and worked part-time or full-time. None smoked, alcohol intake was limited (maximum recorded was four glasses of beer per week), and all subjects ate an adequate caloric, wellbalanced diet that was low in simple sugar and high in complex carbohydrate. They were all in excellent health and averaged 31 years of age (range 24 to 38). Preconceptional weight and height ranged between 42.3 and 78.4 kg and between 155 and 185 em, respectively. Most (128/131) had a normal menstrual pattern; 52% of the populace were nulliparous and 47% were primiparous. Two subjects were secundiparous. The only obstetric risk factors included one subject with a history of diethylstilbestrol exposure, two with a history of bulimia in college, and one with a prior preterm delivery. Data on family obstetric history were not obtained, but there were no between-group differences in the distribution of birth orders, birth weights, or route of delivery of the subjects themselves. All subjects were fit as assessed by preconceptional morning pulse rate (range 48 to 62 beats/min), maximal oxygen consumption (range 43 to 68 mllkg/min), weight for height (range of ponderal index 1.06 to 1.38), and percent body fat (range 10% to 24%). When referenced to current normative standards,1O all subjects had maximum oxygen consumptions in the upper 15% of the overall populace with an average of 54.3 mllkg/min. There were no significance between-group differences in any of these demographic, morphometric, lifestyle, and obstetric variables or in the four objective indices of fitness. In fact, the only two discernible between-group differences were that the women who discontinued their regular exercise regimen in early pregnancy had an overall level of exercise performance before conception that averaged 25% less than that of the women who continued their regular regimen throughout pregnancy (Table I) and their average pregnancy weight gain (17.2 kg) was 3.6 kg greater than that of those who continued exercise (13.6 kg). Maternal exercise performance. Before conception running performance ranged between 14 and 68 km each week at a pace between 3.9 and 6.1 min/km and an intensity ranging between 51 % and 83% of maximum. Participation in aerobics ranged between 3 and ~"I 11 sessions each week at an intensity between 54% and 90% of maximum during the 25- to 30-minute highintensity phase of the workout. The mean group pulse rate was 166 beats/min during both aerobics and running, but there was a great deal of individual variation with individual average exercise pulse rates ranging between 122 and 190 beats/min. The relationship between pulse rate and exercise intensity was extremely variable such that a pulse rate of 140 beats/min for
Endurance exercise and labor
Volume 163 Number 6, Part I
1801
Table I. Maternal exercise performance Control
(N = 44)
Duration-intensity index before pregnancy During pregnancy* (%) Last half of pregnancy* (%) 9-10 mo of pregnancy* (%)
9840 :t 14:t 5 :t 2 :t
303 17 10 3
Exercise (N = 87)
13,070 68 65 60
:t :t :t :t
332 16 17 18
Significance
0.01 0.01 0.01 0.01
Values are mean :t SD. *Percent of prep regnancy value.
different individuals represented an oxygen consumption that ranged between 42% and 73% of measured maximum capacity. During the first half of pregnancy the intensity of exercise was maintained at or near preconceptional levels (51 % to 90% of maximum) in the continued exercise group. However there was an average decrease in running distance and number of a_ez.:obics classes to 29 km/wk and 4.8 classes per week, resulting in a 23% average reduction in the time spent in exercise during the first half of pregnancy. The relationship between exercise intensity and pulse rate became more variable. At 8 and 16 weeks a pulse rate of 140 beats/min for different individuals represented an oxygen consumption that ranged between 31 % and 76% of preconceptional maximum capacity. During the latter half of pregnancy the range of intensity decreased to 50% to 76% of maximum capacity, but the range of the time spent in exercise increased (40% to 160% of preconceptional duration). As a result the average running distance and overall aerobics effort remained stable. Again there was wide individual variation in both pulse rate and its relationship to exercise intensity. Individual average pulse rates during exercise ranged between 110 and 187 beats/min, and a rate of 140 beats/min for different individuals represented an oxygen consumption that ranged between 35% and 68% of preconceptional measured maximum capacity. Thus during pregnancy the slope of the relationship between individual pulse rate and exercise intensity, measured as a percentage of preconceptional maximum absolute oxygen consumption, changed in different directions at different time points in pregnancy, and individual average pulse rates, which ranged between 110 and 195 during exercise in pregnancy, were not by themselves an accurate index of individual exercise intensity. The individual range of overall exercise performance for the entire pregnancy ranged between 50% and 109% of preconceptional levels. For the latter half of pregnancy the range in individual overall performance was 50% to 122% of preconceptional levels. Mean values for the entire group are listed in Table I for the entire pregnancy, the last 5 months, and last 2 months. Although the women who discontinued regular exercise had an overall preconceptional performance
level that averaged 25% less than that of those who continued, their overall level of performance still represented an average of 26 km/week for the runners and an average of four or five classes per week for those who performed aerobics at similar intensities. The majority of these women (n = 37) spontaneously discontinued exercise in early pregnancy for one of two reasons. First, dealing with the extreme fatigue and nausea of early pregnancy completely abolished their desire to exercise early on, and they simply never prioritized the time to begin their regular exercise regimen again during pregnancy. Second, they could not cope emotionally with the reduction in performance level suggested by their physicians or their own uncertainties concerning the potential impact of the exercise on the pregnancy, which were reinforced at the initial prenatal visit. As a result they simply stopped until after delivery. In the remainder minor injury, job pressures, or paternal concerns played a major role. As a group (Table I) their average level of overall performance fell to 2% to 5% of preconceptionallevels by the end of the fifth lunar month. Onset of labor. As detailed in Table II, continuing the ballistic motion associated with running and aerobics throughout pregnancy did not increase the incidence of either the onset of labor before 37V2 weeks of gestation were completed or membrane rupture before the onset of perceived labor. The incidence of spontaneous membrane rupture that eventually necessitated induction of labor was also similar in the two groups. However, the onset of labor at or near term occurred 5 days earlier on average in the women who continued exercise. When examined individually within groups, prepregnancy weight, pregnancy weight gain, parity, preconceptional or pregnant level of exercise performance, and exercise type (aerobics or running) did not have a significant effect on gestational length (all individual R2 values 4000 gm was associated with an increased incidence of protraction disorders and operative delivery. Within the exercise-continued group there was no detectable relationship between birth weight and obstetric intervention with birth weight cutoffs of 3500 and 3750 gm (only one infant weighed >4000 gm). Within the overall populace there was a significant relationship (r 2 = 0.2768) between birth weight and pregnancy weight gain. As discussed elsewhere, 11 this correlation is due to the independent effects of exercise on both parameters.
Comment These data negate the initial hypothesis and clearly indicate that, in physically fit women who performed aerobics or ran on a regular basis before pregnancy, continuing a regular running or aerobics exercise program above a maintenance level throughout pregnancy had a beneficial effect on multiple aspects of the course and outcome of labor. Overall, continued exercise was
Endurance exercise and labor
Volume 163 Number 6, Part 1
1803
Table IV. Management-Vaginal deliveries only Control
Parameter
Exercise
(N = 31)
382 ± 302 ± 52% (n 29% (n
Active labor (min) (mean ± SD) Active first stage (min) (mean ± SD) Parous Forceps use Episiotomy done Epidural anesthetic use Abnormal labor pattern
275 191 = 16)
Significance
264 ± 149 223 ± 134 53% (n = 43)
0.01 0.01 NS 0.01 0.01 0.01 0.01
6% (n = 46% (n = 29% (n = 20% (n =
= 9) 81% (n = 25) 41% (n = 13) 35% (n = II)
Actual number of cases is shown in parentheses. Active labor, 4 em dilatation
(N = 82)
to
5)
38) 24) 16)
delivery.
Active first stage, 4 to' 10 em dilatation.
Table V. Fetal condition and outcome Parameter
Control (N = 44)
Exercise (N = 87)
Significance
Meconium in fluid Abnormal heart rate* Nuchal cord 1 min Apgar score
