A Clinical Approach to Exercise During Pregnancy

A narrative review of exercise dose during pregnancy

The current recommendations for prenatal exercise dose align with those from the American College of Sports Medicine; 150 min of moderate intensity every week of pregnancy. However, recent works suggest there may be a dose-dependent beneficial effect for mother and offspring; maternal and offspring health outcomes respond differently to low, medium, and high doses of prenatal exercise. It is, therefore, our aim to summarize the published evidence (years 1950-2023) for five metrics of prenatal exercise training commonly reported, that is, "FITT-V": Frequency (number of sessions), Intensity (metabolic equivalents "METs"), Time (duration of sessions), Type (exercise mode), Volume (exercise MET*mins). The target audience includes clinicians and health care professionals, as well as exercise professionals and physiologists. Data suggest that moderate exercise frequency (3-4 times weekly) appears safe and efficacious for mother and offspring, while there is contradictory evidence for the safety and further benefit of increased frequency beyond 5 sessions per week. Moderate (3-6 METs) and vigorous (>6 METs) intensity prenatal exercise have been shown to promote maternal and offspring health, while little research has been performed on low-intensity (<3 METs) exercise. Exercise sessions lasting less than 1 hr are safe for mother and fetus, while longer-duration exercise should be carefully considered and monitored. Taken together, aerobic, resistance, or a combination of exercise types is well tolerated at medium-to-high volumes and offers a variety of type-specific benefits. Still, research is needed to define (1) the "minimum" effective dose of exercise for mother and offspring health, as well as (2) the maximum tolerable dose from which more benefits may be seen. Additionally, there is a lack of randomized controlled trials addressing exercise doses during the three trimesters of pregnancy. Further, the protocols adopted in research studies should be more standardized and tested for efficacy in different populations of gravid women.

Origins in the Womb: Potential Role of the Physical Therapist in Modulating the Deleterious Effects of Obesity on Maternal and Offspring Health Through Movement Promotion and Prescription During Pregnancy

Maternal obesity and associated metabolic disease contribute to adverse outcomes in women and their offspring, and many of these outcomes have significant acute and chronic implications for both mother and neonate. Targeted movement (ie, physical activity or exercise training) during pregnancy has been shown to be safe and effective for improving many of these outcomes in women at a healthy weight and women who are obese. However, movement prescription and advice during pregnancy are often not addressed by health care providers; this situation creates a unique opportunity for physical therapists to use their expertise in movement with patients who are pregnant. The objective of this article is to briefly review the adverse maternal and neonatal outcomes associated with maternal obesity, the benefits of intentional maternal movement during pregnancy for women who are obese, the evidence-based guidelines for prescribing intentional movement during pregnancy for women who are obese, and the potential for physical therapists to become the driving force behind a necessary increase in movement levels in women who are pregnant. Physical therapists can play a significant role in encouraging movement in women who are healthy and women who have metabolic challenges during pregnancy and thus assist in combating the vicious cycle of obesity by improving maternal and offspring health.

Cardiac Physiology of Pregnancy

Although the physiology of the heart and vascular system has not changed, there are many things we have learned and are still learning today. Research related to heart adaptations during pregnancy has been performed since the 1930s. Since the mid-1950s, researchers began to look at changes in the maternal cardiovascular system during exercise while pregnant. Research related to exercise during pregnancy and offspring heart development began and has continued since the 1970s. We will review the normal female cardiovascular system adaptations to pregnancy in general. Additionally, topics related to maternal cardiac adaptations to pregnancy during acute exercise, as well as the chronic conditioning response from exercise training will be explored. Since physical activity during pregnancy influences fetal development, the fetal cardiac development will be discussed in regards to acute and chronic maternal exercise. Similarly, the influence of various types of maternal exercise on acute and chronic fetal heart responses will be described. Briefly, the topics related to how and if there is maternal-fetal synchrony will be explained. Lastly, the developmental changes of the fetal cardiovascular system that persist after birth will be explored. Overall, the article will discuss maternal cardiac physiology related to changes with normal pregnancy, and exercise during pregnancy, as well as fetal cardiac physiology related to changes with normal development, and exercise during pregnancy as well as developmental changes in offspring after birth.

Fetal and maternal cardiac responses to physical activity and exercise during pregnancy

Since the 1970s, researchers have studied the influence of exercise during pregnancy on offspring heart development. With the knowledge and current evidence of fetal programming effects, research has demonstrated that exercise is safe and beneficial for mother, fetus, and neonate. Predominantly, research has focused on maternal and fetal cardiac adaptations related to aerobic exercise during pregnancy; less is known regarding the effects of resistance or combination (aerobic and resistance) training during pregnancy. Ongoing research is focusing on fetal responses to different intensity, duration and modes of maternal exercise throughout pregnancy. This article will summarize our current state of knowledge regarding the influence of exercise intensity, duration, and modes during pregnancy on maternal and fetal cardiac responses.

A selective review of prenatal exercise guidelines since the 1950s until present: Written for women, health care professionals, and female athletes

BACKGROUND

Traditional society values have long-held the notion that the pregnant woman is construed as a risk to her growing fetus and is solely responsible for controlling this risk to ensure a healthy pregnancy. It is hard to ignore the participation of pregnant women in sport and exercise today, especially in high-level sports and popular fitness programs such as CrossFit™. This challenges both traditional and modern prenatal exercise guidelines from health care professionals and governing health agencies. The guidelines and perceived limitations of prenatal exercise have drastically evolved since the 1950s.

AIM

The goal of this paper is to bring awareness to the idea that much of the information regarding exercise safety during pregnancy is hypersensitive and dated, and the earlier guidelines had no scientific rigor. Research is needed on the upper limits of exercise intensity and exercise frequency, as well as their potential risks (if any) on the woman or fetus.

DISCUSSION

Pregnant women are physically capable of much more than what was once thought. There is still disagreement about the types of exercise deemed appropriate, the stage at which exercise should begin and cease, the frequency of exercise sessions, as well as the optimal level of intensity during prenatal exercise.

CONCLUSION

Research is needed to determine the upper limits of exercise frequency and intensity for pregnant women who are already trained. Healthy women and female athletes can usually maintain their regular training regime once they become pregnant.

Maternal physical activity before and during the prenatal period and the offspring's academic performance in youth. The UP&DOWN study

OBJECTIVE

To examine the association of maternal physical activity before and during pregnancy with academic performance in youth.

METHODS

This study included 1868 youth (6-18 years) and their mothers. Mothers recalled their physical activity before and during pregnancy. Mothers were categorized into four groups: "remained active", "became inactive", "became active" and "remained inactive". Academic performance was assessed through school records.

RESULTS

Boys whose mothers practiced physical activity before or during pregnancy had significantly higher scores in academic performance indicators independently of physical activity, fitness, current body mass index (BMI) and birthweight than those whose mothers did not practice physical activity before or during pregnancy (all p < 0.05). In addition, boys whose mothers remained active had higher scores in all academic indicators (ranging from +0.358 to +0.543) than boys whose mothers remained inactive. Boys whose mothers remained active had higher scores in Language (score +0.546; 95% CI, 0.150-0.940), average of Math and Language (score +0.468; 95% CI, 0.100-0.836) and grade point average (GPA) (score +0.368; 95% CI, 0.092-0.644) than boys whose mothers became active.

CONCLUSIONS

Maternal physical activity before and during pregnancy may positively influence youth's academic performance. Continuing maternal physical activity practice during pregnancy may have greater benefits for youth's academic performance.

Changes in leisure time physical activity during pregnancy compared to the prior year

To quantify changes in leisure time physical activity (LTPA) type, frequency, duration and intensity during the first half of pregnancy as compared with the year prior to pregnancy. A cross sectional study was conducted at the Maternal University Hospital in Granada, Spain. A total of 1,175 healthy pregnant women attending a scheduled visit during the 20-22nd gestational week were enrolled in the study. Information about socio-demographic, obstetric and life-style variables during the previous year and the first half of pregnancy were collected. LTPA was quantified by assigning metabolic equivalents to each activity according to frequency, intensity and duration. The prevalence of women who met the optimal physical activity recommendations before and during pregnancy was calculated, and the McNemar-Bowker symmetry test was used to assess changes in type, frequency, intensity and duration of activities between the two periods. Some sort of LTPA was performed before and during pregnancy by 68.6% of the pregnant women. Respectively, just 27.5% and 19.4% of women fulfilled LTPA recommendations prior to pregnancy and during pregnancy; 12.6% of the women meeting recommendations prior to pregnancy later did not meet those recommendations during gestation, and 4.5% showed the reverse trend. A light increase in walking as a LTPA, and a decrease in the rest of the LTPA type activities, were seen during pregnancy. Some 13.4% of women changed from moderate--the year before- to light LTPA- during pregnancy. Pregnancy involved a decrease in LTPA, not only regarding frequency, but also duration and intensity.

Compliance with leisure-time physical activity recommendations in pregnant women

OBJECTIVE

The aim of this study was to identify the prevalence and factors associated with the performance of minimal beneficial leisure-time physical activity in the first half of pregnancy according to the criteria of the American College of Sport and Medicine (ACSM) and the American College of Obstetricians and Gynecologists (ACOG).

MATERIAL AND METHODS

This was a cross-sectional study carried out at the Maternal and Neonatal University Hospital in Granada, which services the whole population of the hospital reference area. We studied 1,175 healthy pregnant women aged over 18 years. Information about sociodemographics, lifestyles, obstetric antecedents and anthropometric variables were collected. The amount of leisure-time physical activity was quantified by assigning metabolic equivalents to each activity. The ACSM and ACOG criteria were used to define optimal physical activity in the first half of pregnancy. The frequency of compliance for both criteria was estimated. Multiple logistic regression models were fitted to study the factors associated with the recommendations.

RESULTS

Only 20.3% (95% confidence interval 15.50-26.10) of the women complied with ACOG criteria. More women complied with ACSM recommendations (70.8%, 95% confidence interval 67.5-73.8), which are less restrictive criteria. Women aged 30 years old or older and those with a university degree tended to devote more time to exercising according to both recommendations.

CONCLUSION

The prevalence of pregnant women who performed minimal beneficial leisure-time physical activity was lower with the dominant and more accepted criteria. It is necessary to encourage physical activity, mainly among those who are younger, and those with lower levels of educational attainment.

Aerobic exercise during pregnancy influences fetal cardiac autonomic control of heart rate and heart rate variability

BACKGROUND

Previous studies using ultrasound technology showed that fetal heart rate (HR) may be responsive to maternal aerobic exercise. Although it is recognized that cardiac autonomic control may be influenced by the intrauterine environment, little is known about how maternal exercise affects fetal heart development.

AIMS

This study tested the hypothesis that regular maternal exercise throughout gestation influences fetal cardiac autonomic control of HR and heart rate variability (HRV) when compared to fetuses of non-exercising women.

STUDY DESIGN

Magnetocardiograms (MCGs) were recorded using a dedicated fetal biomagnetometer at 28, 32 and 36 weeks gestational age (GA) from 26 regularly exercising (>30 min of aerobic exercise, 3x per week) and 35 healthy, non-exercising pregnant women. Fetal MCG was isolated and normal R-peaks were marked to derive fetal HR and HRV in the time and frequency domains. We applied a mixed-effects model to investigate the effects of exercise, GA and fetal activity state.

RESULTS

At 36 weeks GA, during the active fetal state, fetal HR was significantly lower in the exercise group (p=<0.0006). Post-hoc comparisons showed significantly increased HRV in the exercise group during the active fetal state at 36 weeks GA for both time and frequency domain measures.

CONCLUSION

These results indicate that regular maternal exercise throughout gestation results in significantly lower fetal HR and increased HRV.

Design of FitFor2 study: the effects of an exercise program on insulin sensitivity and plasma glucose levels in pregnant women at high risk for gestational diabetes

Background

Pregnancy is a period in the life of women that is often associated with decreased daily physical activity and/or exercise. However, maintaining adequate levels of daily physical activity during pregnancy is important for mother and child. Studies suggest that moderate daily physical activity and exercise during pregnancy are associated with reductions in the risk of gestational diabetes mellitus (GDM). However, at present, physical activity is not routinely advised to pregnant women at risk for gestational diabetes in the Netherlands. In FitFor2-study we aim to assess whether an exercise program can improve insulin sensitivity and fasting plasma glucose levels of women at high risk for gestational diabetes, assuming that this will lower their risk of gestational diabetes.

Methods

The FitFor2-study is a randomised controlled trial. Women who visit one of the participating hospitals or midwifery practices and who are at risk for gestational diabetes are eligible to participate. After baseline measurement they are randomly allocated to in the intervention or control group. The intervention group receives an exercise program twice a week in addition to usual care. The exercise program consist of aerobic and strength exercises and takes place under close supervision of a physiotherapist. Data are collected at 15, 24 and 32 weeks of pregnancy and 12 weeks after delivery. Primary maternal outcome measures are fasting plasma glucose and relative increase in insulin resistance. Primary neonatal outcome is birth weight. Secondary outcome measures are: maternal serum triglycerides, HDL, cholesterol, HbA1c, maternal weight gain during pregnancy, maternal physical activity level, foetal growth.

Discussion

If the FitFor2 intervention program proves to be effective, obstetricians and midwives should refer women at risk for GDM to a special exercise program. Exercise programs for pregnant women under supervision of an experienced trainer are already available in the Netherlands, and these programs could be adjusted easily for this target group. Furthermore, the costs of these programs should be refunded by including them in the basic health care cost reimbursement schemes.

Trial registration

NTR1139

Long-term outcome after exercising throughout pregnancy: fitness and cardiovascular risk

OBJECTIVE

The objective of the study was to test the null hypothesis that continuing vigorous weight-bearing exercise throughout pregnancy has no discernible long-term effect on indices of fitness and/or cardiovascular risk.

STUDY DESIGN

This was a follow-up observational study of the fitness and cardiovascular risk profile of 39 women conducted on the General Clinical Research Center at the University of Vermont. Data were analyzed using the paired Student t test, analysis of variance, and linear regression.

RESULTS

Women who voluntarily maintain their exercise regimen during pregnancy continue to exercise over time at a higher level than those who stop. Over time they also gain less weight (3.4 vs 9.9 kg), deposit less fat (2.2 vs 6.7 kg), have increased fitness, and have a lower cardiovascular risk profile than those who stop.

CONCLUSION

Women who continue weight-bearing exercise during pregnancy maintain their long-term fitness and have a low cardiovascular risk profile in the perimenopausal period.

Impact of physical activity during pregnancy and postpartum on chronic disease risk

Research over the past 20 years has focused on the safety of physical activity during pregnancy. Guidelines for health care providers and pregnant/postpartum women have been developed from the results of these studies. The overwhelming results of most studies have shown few negative effects on the pregnancy of a healthy gravida, but rather, be beneficial to the maternal-fetal unit. Recently, researchers have begun to consider the role of maternal physical activity in a more traditional chronic disease prevention model, for both mother and offspring. To address the key issues related to the role of physical activity during pregnancy and postpartum on chronic disease risk, the American College of Sports Medicine convened a Scientific Roundtable at Michigan State University in East Lansing, MI. Topics included preeclampsia, gestational diabetes, breastfeeding and weight loss, musculoskeletal disorders, mental health, and offspring health and development.

Influence of Endurance Exercise and Diet on Human Placental Development and Fetal Growth

The delivery of oxygen and substrate to the maternal-fetal interphase is the major maternal environmental stimulus which either up- or down-regulates feto-placental growth. During pregnancy, sustained exercise sessions cause an intermittent reduction in oxygen and substrate delivery to the interphase that may exceed 50% during the exercise but, it is probable that regular bouts of sustained exercise or exercise training may improve oxygen and substrate delivery at rest. The type of maternal carbohydrate intake (low- versus high-glycemic sources) and food intake frequency also influence substrate availability through their effects on maternal blood glucose levels and insulin sensitivity. As a result, different exercise regimens and/or different types of carbohydrate intake modify feto-placental growth. The magnitude and direction of the effect is determined by their average 24-h effect on oxygen and substrate availability at different time-points in pregnancy. In general, exercise in early and mid pregnancy stimulates placental growth while the relative amount of exercise in late pregnancy determines its effect on late fetal growth. Low-glycemic food sources in the diet decrease growth rate and size at birth while high-glycemic food sources increase it. Thus, it may be possible to improve pregnancy outcomes in both healthy, low-risk women and a variety of high-risk populaces by simply modifying maternal physical activity and dietary carbohydrate intake during pregnancy.

The effect of maternal exercise on uterine artery velocimetry waveforms

One hundred and two subjects in the second half of pregnancy were subject to an acute exercise test lasting 5 minutes on an upright bicycle ergometer. The pulsatility index (using Doppler ultrasound) of the right uterine artery was analysed before exercise and at 2, 4, 6, 8, 10, 12, 16, 20, 24 and 30 minutes after exercise. The mean exercise intensity achieved was 67.2% of sub-maximal exercise (range 51-90%). At 2 minutes post-exercise, the mean uterine artery pulsatility index was increased from the baseline value, reaching a maximum of 0.64 at 8 minutes (baseline 0.583). After 8 minutes there was a gradual decrease in the pulsatility index, and at 24 and 30 minutes the values were significantly lower (P < 0.001 and P < 0.001 respectively). Smokers had significantly higher pulsatility index values than non-smokers (P < 0.004). Primigravidae also had lower resistance indices compared with multigravidae (P < 0.001). We conclude that exercise in the second half of pregnancy appears to cause a transient increase in the maternal uterine artery pulsatility index. We also believe that at this level of exercise intensity there was no evidence of harmful effects on maternal uterine blood flow.

The effects of maternal exercise on fetal oxygenation and feto-placental growth

Sustained bouts of maternal exercise during pregnancy cause an acute reduction in oxygen and nutrient delivery to the placental site. The decreased flow also initiates a slight fall in intervillous and fetal pO2 which initiates a fetal sympathetic response. This, coupled with hemoconcentration and improved placental perfusion balance, maintains fetal tissue perfusion and oxygen uptake. Exercise training during pregnancy (regular bouts of sustained exercise) increases resting maternal (and perhaps fetal) plasma volume, intervillous space blood volume, cardiac output and placental function. These changes buffer the acute reductions in oxygen and nutrient delivery during exercise and probably increase 24 h nutrient delivery to the placental site. Thus, the effect of any given exercise regimen on fetal growth and size at birth is dependent on the type, frequency, intensity and duration of the exercise as well as the time point in the pregnancy when the exercise is performed. Maternal carbohydrate intake is yet another modifying factor. Beginning a moderate exercise regimen increases both anatomic markers of placental function and size at birth while maintaining a rigorous exercise regimen throughout pregnancy selectively reduces growth of the fetal fat organ and size at birth. Likewise, decreasing exercise performance in late-pregnancy increases size at birth while increasing exercise performance decreases it. Finally, the infants born of exercising women who eat carbohydrates which elevate 24 h blood glucose levels are large at birth irrespective of exercise performance.

SMA statement the benefits and risks of exercise during pregnancy. Sport Medicine Australia

There are numerous benefits to pregnant women of remaining active during pregnancy. These include improved weight control and maintenance of fitness. There may also be benefits in terms of reduced risk of development of gestational diabetes meilitus and improved psychological functioning. Moderate intensity aerobic exercise has been shown to be safe in pregnancy, with a number of studies now indicating that for trained athletes it may be possible to exercise at a higher level than is currently recommended by the American College of Obstetricians and Gynecologists. Studies of resistance training, incorporating moderate weights and avoiding maximal isometnc contractions, have shown no adverse outcomes. There may be benefits of increased strength and flexibility. The risk of neural tube defects due to exercise-induced hyperthermia that is suggested by animal studies is less likely in women, because of more effective mechanisms of heat dissipation in humans. There is accumulating evidence to suggest that participation in moderate intensity exercise throughout pregnancy may enhance birth weight, while more severe or frequent exercise, maintained for longer into the pregnancy: may result in lighter babies. There have been no reports of foetal injury or death in relation to trauma or contact during sporting activities. Despite this, a risk of severe blunt trauma is present in some sporting situations as pregnancy progresses. Exercise and lactation are compatible in the post-partum period, providing adequate calories are consumed. Considerations of pelvic floor function and type of delivery are relevant in planning a return to certain types of exercise at this time.

The benefits of physical activity during pregnancy

The aims of this paper are (1) to comment on the evidence relating to the health risks and benefits of physical activity (PA) for pregnant women and their unborn foetuses. and (2) to discuss the public health benefits of participation in appropriate physical activity during pregnancy. Evidence from recent original research and review papers suggests that there are potential benefits of appropriate PA in terms of maternal weight control and fitness, which are likely to have significant long term public health benefits. Concerns about the potential ill-effects of PA during pregnancy, such as hyperthermia, shortened gestational age and decreased birth weight are not supported by the most recent scientific reviews. The physiological adaptations to exercise during pregnancy appear to protect the foetus from potential harm and, while an upper level of safe activity has not been established, the benefits of continuing to be active during pregnancy appear to outweigh any potential risks. All decisions about participation in physical activity during pregnancy should however be made by women in consultation with their medical advisers.

The benefits of exercise for women

This article describes the benefits of exercise, including why exercise improves blood pressure control, how it may reduce the risk for cancer, and increase mental health, and how it may improve bone mineral density. The article also explores the gender-independent and gender-specific benefits of exercise for women.

Exercise during pregnancy. A clinical update

Research dealing with exercise during pregnancy continues to demonstrate marked benefits for mother and fetus. The type, intensity, frequency, and duration of the exercise seem to be important determinants of its beneficial effects. Maternal benefits include improved cardiovascular function, limited weight gain and fat retention, improved attitude and mental state, easier and less complicated labor, quick recovery, and improved fitness. Fetal benefits may include decreased growth of the fat organ, improved stress tolerance, and advanced neurobehavioral maturation. Currently, the offspring are leaner at 5 years of age and have a slightly better neurodevelopmental outcome. Postpubertal effects are still unknown. In the absence of medical contraindications, women should be encouraged to maintain their prepregnancy activity level.

Risk assessment

Risk assessment is the process by which clinicians screen for conditions that, if unmanaged, result in complications of pregnancy or adverse birth outcomes and for which an intervention would improve the well-being of the mother, child, and family. One of the major US health care goals is that by the year 2000, at least 90% of pregnant women will receive risk appropriate care. This article discusses the major risks to the mother and child during pregnancy, and presents tools to assess pregnancy well-being.

Musculoskeletal rehabilitation and sports medicine. 4. Miscellaneous sports medicine topics

This self-directed learning module highlights new advances in this topic area. It is part of the chapter on musculoskeletal rehabilitation and sports medicine in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. This article discusses physiatric duties as a team physician, preparticipation physical examinations, ergogenic aids, heat-related illness, pediatric sports injuries, female sports injuries, and sports medicine topics pertinent to geriatric and physically or mentally challenged athletes. New advances covered in this section include use of creatine, guidelines for the preparticipation examination, sudden cardiac athletic death, pediatric and female anterior cruciate ligament injuries, the female athlete triad, spine screening in Down syndrome athletes, and "boosting" in athletes with spinal cord injury.

The effect of positive and negative health behavior during gestation on pregnancy outcome

This study examined the effects of substance use (alcohol, tobacco and/or drugs (cocaine and/or marijuana)) and healthy maternal behavior (prenatal care, prenatal class, vitamins, regular exercise) during gestation on pregnancy outcome. Live births from the nationally representative 1988 National Maternal and Infant Health Survey were analyzed. Pregnancy outcomes (infant birth weight, weeks gestation, one and five minute Apgar scores, whether or not the infant was transferred to another hospital after delivery and whether or not the infant was rehospitalized) were studied in multiple linear regression and logistic regression models. The relationship of the interaction of substance use and healthy behaviors and outcome was studied in all models. It was found that women engaging in substance use while pregnant were less likely to engage in healthy behavior. However, in general, engaging in healthy behaviors had the largest positive effects on outcome for those women who engaged in multiple substance use while pregnant. Significant interactions between healthy and unhealthy behavior were found for birth weight, weeks gestation and five minute Apgar scores, indicating that engaging in positive health behavior may help moderate some of the deleterious consequences of substance use during pregnancy.

The Female Athlete: Evaluation and Treatment of Sports-Related Problems

Although many of the problems faced by the female athlete affect the male athlete as well, some occur exclusively or more commonly in women. These include spondylolisthesis, stress fractures in the pelvis and hip, and pelvic floor dysfunction. Female athletes are also more likely to have patellofemoral problems, noncontact anterior cruciate ligament tears, and bunions. For many of these conditions, the relative influences of osseous anatomy, ligamentous laxity, and the effect of sex hormones have not yet been established. There are also problems related specifically to the menstrual cycle and pregnancy. Amenorrhea is present in up to 20% of vigorously exercising women. The term "female athlete triad" has been coined to describe the complex interplay of menstrual irregularity, disordered eating, and premature osteoporosis seen in the female athlete. Many of the concerns related to exercise during pregnancy focus on the safety of the fetus rather than the athlete herself. Musculoskeletal problems in the physically active pregnant woman are related to weight gain, ligamentous relaxation, lordosis, and change in the center of gravity.

Maternal and fetal cardiovascular response to exercise during pregnancy

With the two-dimensional Doppler echocardiogram and M-mode echocardiogram, one can study maternal and fetal cardiovascular physiology during rest and exercise. Using such noninvasive techniques, studies indicate that left ventricular function is maintained even during vigorous bicycle exercise in healthy pregnant subjects during the second half of pregnancy. In early pregnancy, the left ventricle adapts to strenuous bicycle exercise by increasing its contractile reserve, enhancing ventricular emptying, whereas in late pregnancy, the left ventricle increases its preload reserve without significantly increasing its contractile reserve. Thus, women are "cardiovascularly" disadvantaged early in pregnancy. Using Doppler signals, early (E-passive) flow and late peak (A-active) flow reflect left ventricular diastolic filling properties. Using such techniques, we found that diastolic filling patterns are significantly influenced by pregnancy and that each trimester influences these diastolic filling patterns during upright bicycle exercise. Doppler studies of uteroplacental circulation during or after exercise have yielded conflicting results. Some have described an increase in "the vascular resistance" of this pelvic bed during strenuous exercise, whereas others have not. It seems safe to conclude that more studies are needed to elucidate this problem. Exercise does not seem to influence the resistivity index of the umbilical artery in either singleton or twins, and may even cause it to decrease. Ventricular diastolic filling properties of the fetal heart do not seem to be influenced by maternal bicycle exercise. Further studies are needed to determine if less active pregnant subjects, women with chronic hypertensive disorders, women with sickle cell anemia, or women with insulin-dependent diabetes adapt to exercise as well as their "normal" counterparts.

Pregnancy outcome: physical activities inside versus outside the workplace

There is concern that the thermal, cardiovascular, metabolic, and biophysical changes which accompany physical activity may have detrimental effects on both mother and fetus. Research focused on physical activity in the workplace has identified four specific physical stresses (quiet standing, long hours, protracted ambulation, and heavy lifting) that are associated with an increased incidence of both prematurity and low birth weight. The physiological basis for these is believed to be that these activities cause intermittent but protracted reductions in uterine blood flow. Research focused on recreational physical activity during pregnancy has not identified similar associations. Indeed, these data indicate that the overall impact of regular recreational exercise on pregnancy outcome is positive for both mother and fetus. The physiological basis for these beneficial effects is believed to be that the interaction between the physiological adaptations to both exercise and pregnancy improve maternal cardiovascular reserve, maternal mechanisms for heat dissipation, and placental growth and functional capacity. Finally, there is preliminary evidence suggesting that the vibratory and auditory stimuli associated with regular recreational exercise may enhance functional maturation of the fetal brain.

The interaction between regular exercise and selected aspects of women's health

The public health initiative to increase women's participation in regular recreational exercise to the 90% level raises multiple theoretic concerns about its impact on the reproductive health of women. However, at all points in a woman's life the overall effect of regular exercise to appetite appears to be beneficial rather than harmful, and in the absence of other stressors, exercise performance must significantly exceed usual recreational levels to have an adverse effect on any aspect of a woman's reproductive life. Therefore even in elite athletes abnormalities of any part of the reproductive process (puberty, menstrual cyclicity, pregnancy, lactation, and menopause) should not be attributed solely to exercise without complete evaluation. While generally beneficial, the interaction between exercise and skeletal integrity is influenced by hormonal status and multiple exercise variables. Thus, whereas regular exercise at all ages appears to provide both short- and long-term benefit, the characteristics of the exercise regimen need to vary at different time points.

The effect of regular maternal exercise on erythropoietin in cord blood and amniotic fluid

OBJECTIVE

Our purpose was to test the hypothesis that continuing regular, high-intensity exercise until the onset of labor produces significant fetal hypoxemia, as evidenced by elevated erythropoietin levels in the fetal compartment.

STUDY DESIGN

Erythropoietin levels were measured in samples of amniotic fluid and cord blood obtained from fetuses born to 31 exercising women and 29 matched controls.

RESULTS

Erythropoietin levels (mean +/- SEM) in amniotic fluid obtained at the time of membrane rupture (9 +/- 2 vs 11 +/- 2 mU/ml) and in cord blood (38 +/- 6 vs 53 +/- 16 mU/ml) and amniotic fluid at delivery (9 +/- 1 vs 24 +/- 12 mU/ml) were no different in women who exercised regularly until the onset of labor. In both groups the majority of elevated cord blood levels (> 50 mU/ml) could be explained by labor events. Amniotic fluid erythropoietin levels correlated directly (r = 0.52) with cord blood hematocrit and increased slowly during labor.

CONCLUSION

We conclude that the initial hypothesis is incorrect and speculate that cord blood erythropoietin reflects fetal oxygenation during labor, whereas amniotic fluid erythropoietin primarily reflects the adequacy of oxygenation before the onset of labor.