James F. Clapp

Cardiovascular function before, during, and after the first and subsequent pregnancies

This study was designed to test the hypothesis that the vascular remodeling of pregnancy begins early, persists for at least 1 year after delivery, and is accentuated by a second pregnancy. Serial estimates of heart rate, arterial pressure, left ventricular volumes, cardiac output, and calculated peripheral resistance were obtained before pregnancy, every 8 weeks during pregnancy, and 12, 24, and 52 weeks postpartum in 15 nulliparous and 15 parous women using electrocardiography, automated manometry, and M-mode ultrasound. During pregnancy, body weight increased 14.5 +/- 1.8 kg and returned to prepregnancy values 1 year postpartum. Heart rate peaked at term 15 +/- 1 beat/min above prepregnancy levels (57 +/- 1 beat/min). Mean arterial pressure reached its nadir (-6 +/- 1 mm Hg) at 16 weeks, returning to baseline at term. The increases in left ventricular volumes and cardiac output (2.2 +/- 0.2 L/min) peaked at 24 weeks as did the 500 +/- 29 dynes x cm x s(-5) decrease in peripheral resistance, and their magnitude was significantly greater in the parous women. Postpartum they gradually returned toward baseline but remained significantly different from prepregnancy values in both groups at 1 year. We conclude that cardiovascular adaptations to the initial pregnancy begin early, persist postpartum, and appear to be enhanced by a subsequent pregnancy. We speculate that persistence of these changes may lower cardiovascular risk in later life.

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.

Maternal carbohydrate intake and pregnancy outcome

Experimental evidence indicates that the primary maternal environmental factor that regulates feto-placental growth is substrate delivery to the placental site, which is the product of maternal substrate levels and the rate of placental-bed blood flow. Thus, maternal factors which change either substrate level or flow alter feto-placental growth rate. The best-studied substrate in human pregnancy is glucose, and there is a direct relationship between maternal blood glucose levels and size at birth. Altering the type of carbohydrate eaten (high- v. low-glycaemic sources) changes postprandial glucose and insulin responses in both pregnant and non-pregnant women, and a consistent change in the type of carbohydrate eaten during pregnancy influences both the rate of feto-placental growth and maternal weight gain. Eating primarily high-glycaemic carbohydrate results in feto-placental overgrowth and excessive maternal weight gain, while intake of low-glycaemic carbohydrate produces infants with birth weights between the 25th and the 50th percentile and normal maternal weight gain. The calculated difference in energy retention with similar total energy intakes is of the order of 80,000 kJ. Preliminary information from subsequent metabolic studies indicates that the mechanisms involved include changes in: daily digestible energy requirements (i.e. metabolic efficiency), substrate utilization (glucose oxidation v. lipid oxidation), and insulin resistance and sensitivity. Thus, altering the source of maternal dietary carbohydrate may prove to be a valuable tool in the management of pregnancies at risk for anomalous feto-placental growth and for the prevention and/or treatment of obesity and insulin resistance in the non-pregnant state.

Effects of pregnancy and exercise on concentrations of the metabolic markers tumor necrosis factor α and leptin

Abstract Objective: Pregnancy and exercise have opposite effects on fat mass and insulin resistance. We therefore designed this study to test the hypotheses that exercise during pregnancy alters the pregnancy- associated increases in the levels of tumor necrosis factor α and leptin and that the changes in tumor necrosis factor α and leptin concentrations during pregnancy continue to reflect changes in fat mass. Study Design: The levels of tumor necrosis factor α and leptin were measured longitudinally in a control group of physically active women, a group of women who performed endurance exercises ≥4 times a week throughout pregnancy, and a group of women who initially performed endurance exercises but then stopped exercising during midpregnancy. Exercise was monitored, and longitudinal estimates of maternal total mass and fat mass were obtained. Results: Tumor necrosis factor α levels were lower during pregnancy in the women who exercised, and the same was true for leptin levels. When women stopped exercising, however, both tumor necrosis factor α and leptin concentrations rose at rates comparable to those seen in the physically active control group. Changes in leptin concentration but not those in tumor necrosis factor α concentration correlated with the pregnancy-associated increases in total body and fat mass. Conclusions: Regular weight-bearing exercise during pregnancy suppresses the pregnancy-associated changes normally seen in both tumor necrosis factor α and leptin. The decrease in leptin reflects decreased fat accretion, and we speculate that the changes in tumor necrosis factor α may reflect a change in insulin resistance. (Am J Obstet Gynecol 2000;182:300-6.)

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

BACKGROUNDnPrevious 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.nnnAIMSnThis 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.nnnSTUDY DESIGNnMagnetocardiograms (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.nnnRESULTSnAt 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.nnnCONCLUSIONnThese results indicate that regular maternal exercise throughout gestation results in significantly lower fetal HR and increased HRV.

Neonatal behavioral profile of the offspring of women who continued to exercise regularly throughout pregnancy

OBJECTIVEnThe objective of the study was to test the hypothesis that continuing regular exercise throughout pregnancy alters early neonatal behavior.nnnSTUDY DESIGNnThe offspring of 34 women who exercised were compared with those of 31 demographically similar control subjects. All women had normal antenatal courses. Behavior was assessed at 5 days after birth with the Brazelton Scales.nnnRESULTSnThe offspring of the exercising women performed better in 2 of the 6 behavioral constellations when examined at 5 days after birth. The scores reflecting their ability to orient to environmental stimuli were (mean +/- SEM) 7.6 +/- 0.1 and 6.5 +/- 0. 3, respectively, and the scores reflecting their ability to regulate their state or quiet themselves after sound and light stimuli were 6. 6 +/- 0.2 and 4.9 +/- 0.3, respectively. The scores reflecting habituation (7.9 +/- 0.2 and 8.0 +/- 0.1, respectively), motor organization (5.7 +/- 0.1 and 5.5 +/- 0.1, respectively), autonomic stability (5.9 +/- 0.2 and 5.5 +/- 0.3, respectively), and behavioral state range (4.1 +/- 0.2 and 4.5 +/- 0.3, respectively) were not significantly different.nnnCONCLUSIONSnThese data indicate that the neonates born of exercising mothers have a different neurobehavioral profile as early as the fifth day after birth.

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

OBJECTIVEnOur 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.nnnSTUDY DESIGNnErythropoietin levels were measured in samples of amniotic fluid and cord blood obtained from fetuses born to 31 exercising women and 29 matched controls.nnnRESULTSnErythropoietin 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.nnnCONCLUSIONnWe 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.

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

The public health initiative to increase womens 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 womans 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 womans 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.

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

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

Uterine blood flow during supine rest and exercise after 28 weeks of gestation

Objectiveu2002 To test the null hypothesis that, after 28 weeks of gestation, uterine blood flow during supine rest and supine exercise is no different than uterine blood flow at left‐lateral rest.