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

OBJECTIVE

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.

DESIGN

In vivo experimental study in pregnant women.

SETTING

Department of Obstetrics, MetroHealth Medical Center, Cleveland, OH, USA.

POPULATION

Fourteen, physically active, late-pregnant women who continued supine exercise throughout gestation.

METHODS

Studies were carried out between 29 and 38 weeks of gestation. Maternal blood pressure, maternal heart rate, and ultrasound estimates of volume blood flow in the right ascending branch of the uterine artery were obtained serially at rest in the left-lateral position, at rest in the supine position, during and immediately after 10 minutes of supine exercise, and again at rest in the left-lateral position. Exercise sessions included alternating 60- to 90-second periods of abdominal crunches and leg exercise at moderate/high intensity (Borg's rating of perceived exertion 14 +/- 1).

MAIN OUTCOME MEASURES

Blood pressure, heart rate, and uterine artery volume flow.

RESULTS

Data are presented as the mean +/- SD. Maternal heart rate and blood pressure were unchanged at supine rest but increased during supine exercise (heart rate increased from 76 +/- 9 to 98 +/- 12 beats per minute, mean arterial pressure increased from 81 +/- 6 to 102 +/- 12 mmHg). Volume flow fell from 410 +/- 93 to 267 +/- 73 cc/minute after 5 minutes of supine rest and then, during supine exercise, increased to 355 +/- 125 cc/minute. Uterine artery luminal diameter and blood flow correlated directly with tissue weights at birth (r(2) values between 0.32 and 0.59).

CONCLUSIONS

In physically active women, uterine blood flow decreases during both supine rest and supine exercise but the decrease in the former is twice that seen in the latter.

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.

Running throughout pregnancy: effect on placental villous vascular volume and cell proliferation

Many studies have documented that placental development is altered by a variety of environmental factors which alter placental bed blood flow and/or oxygen delivery. One of these is sustained weight-bearing exercise. The purpose of this investigation was to examine the effects of running throughout pregnancy on villous vascular development and cell proliferation by testing the null hypothesis that continuing a regular running regimen throughout pregnancy has no effect on villous vascular volume or cell proliferation at term. Accordingly, placentae of 11 healthy runners with uncomplicated pregnancies were matched by placental weight, maternal diet and birth weight with those of 11 healthy controls and examined using systematic random sampling and point counting of placental tissues stained immunohistochemically with either an endothelial (CD 31, PECAM-1, endoCam) or a proliferative (Ki-67, MIB-1) marker. The placentae of the runners had greater villous vascular volumes in both absolute (77 +/- 20 cm(3) versus 47 +/- 18 cm(3), p < 0.02) and relative (% of total villous volume: 29 +/- 5% versus 20 +/- 6%, p < 0.003) terms. Likewise, they had a greater proliferation index (45 +/- 14 mitoses/1000 nuclei versus 29 +/- 10 mitoses/1000 nuclei, p < 0.008). We conclude that continuing to run regularly throughout pregnancy increases both absolute and relative villous vascular volume and cell proliferation at term. We also speculate that this exercise effect may have clinical value in cases at risk for anomalous feto-placental growth as increased villous vascular volume should improve feto-placental growth by enhancing placental transfer of oxygen and diffusible substrate.

Fetal cerebellum: US appearance with advancing gestational age

PURPOSE

To evaluate the change in ultrasonographic (US) appearance of the fetal cerebellum with advancing gestation.

MATERIALS AND METHODS

A total of 291 normal fetuses of uncomplicated pregnancies were evaluated at gestational ages (GAs) between 15 and 41 weeks with a 3.75-MHz transabdominal curvilinear probe. After the transcerebellar view was obtained, the transverse cerebellar diameter (TCD) was measured and the images were stored. On hard-copy US images, cerebella were assigned three grades of appearance. These grades were analyzed in relation to GA and TCD. Inter- and intraobserver variations were assessed in 91 randomly selected cases.

RESULTS

Cerebella in 137 (47.1%), 71 (24.4%), and 83 (28.5%) of 291 subjects were classified as grade I (hypoechoic, "eyeglass" shape), grade II (intermediate echogenicity, "dumbbell" outline), and grade III (hyperechoic, "fan" shape), respectively. With advancing gestation, the dominant grade changed from I to III gradually and progressively. The median GA and TCD, respectively, were 22 weeks and 22 mm for grade I, 29 weeks and 35 mm for grade II, and 36 weeks and 46 mm for grade III. These differences were statistically significant (P <.001). The agreements within inter- and intraobserver estimations were 96% (87 of 91) and 95% (86 of 91), respectively.

CONCLUSION

A gradual change in US appearance of the fetal cerebellum is seen with advancing gestation.

Beginning regular exercise in early pregnancy: effect on fetoplacental growth

OBJECTIVE

Our purpose was to test the null hypothesis that beginning regular, moderate-intensity exercise in early pregnancy has no effect on fetoplacental growth.

STUDY DESIGN

Forty-six women who did not exercise regularly were randomly assigned at 8 weeks either to no exercise (n = 24) or to weight-bearing exercise (n = 22) 3 to 5 times a week for the remainder of pregnancy. Outcome variables included antenatal placental growth rate and neonatal and placental morphometric measurements.

RESULTS

The offspring of the exercising women were significantly heavier (corrected birth weight: 3.75 +/- 0.08 kg vs 3.49 +/- 0.07 kg) and longer (51.8 +/- 0.3 cm vs 50.6 +/- 0.3 cm) than those born to control women. The difference in birth weight was the result of an increase in both lean body mass and fat mass. In addition, midtrimester placental growth rate was faster (26 +/- 2 cm(3)/wk vs 21 +/- 1 cm(3)/wk) and morphometric indexes of placental function were greater in the exercise group. There were no significant differences in neonatal percentage body fat, head circumference, ponderal index, or maternal weight gain.

CONCLUSIONS

These data indicate that beginning a moderate regimen of weight-bearing exercise in early pregnancy enhances fetoplacental growth.

Portal vein blood flow-effects of pregnancy, gravity, and exercise

OBJECTIVE

We sought to test the hypotheses that pregnancy increases portal vein blood flow and that regular exercise training during pregnancy limits the flow redistribution away from the splanchnic and uterine circulations in response to either gravitational or exercise-induced hemodynamic stress.

STUDY DESIGN

Portal vein blood flow, which probably reflects changes in uterine blood flow, was estimated with ultrasonography in 6 regularly exercising and 6 physically active control subjects before and during pregnancy after 15 minutes of rest in the left lateral recumbent position, after 5 minutes of standing rest, and immediately and 5 minutes after 20 minutes of treadmill exercise at 55% +/- 3% of maximal aerobic capacity.

RESULTS

Portal vein blood flow rose significantly during early and mid pregnancy at recumbent rest (from 660 +/- 110 to 1090 +/- 120 mL/min), standing rest (580 +/- 70 to 790 +/- 120 mL/min), immediately after exercise (160 +/- 30 to 360 +/- 60 mL/min), and at 5 minutes of recovery (520 +/- 60 to 760 +/- 110 mL/min). Before pregnancy, exercise training did not blunt the decremental effects of either gravity or exercise on portal vein blood flow. During mid and late pregnancy, exercise training had no effect on the fall in portal vein blood flow with gravitational stress, but it markedly reduced the decremental effects of exercise (average for the 2 time points, -510 +/- 80 vs -840 +/- 100 mL/min) and improved recovery at 5 minutes after exercise (940 +/- 140 vs 600 +/- 130 mL/min).

CONCLUSIONS

Portal vein blood flow rises significantly during pregnancy, and flow redistribution away from the splanchnic and uterine circulations in response to severe hemodynamic stress is reduced by exercise training in mid and late pregnancy.

Matrix-assisted laser desorption/ionization mass spectrometric quantification of the mu opioid receptor agonist DAMGO in ovine plasma

The synthetic opioid peptide analog Tyr-D-Ala-Gly-N-methyl-Phe-Gly-ol (DAMGO), which is a mu opioid receptor-selective agonist, was quantified in ovine plasma samples with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), using delayed extraction and a reflectron. The internal standard was pentadeuterated DAMGO. Timed-ion selection was used to select the precursor ion. The analysis of the post-source decay fragments improved the detection sensitivity, and the use of the precursor-product ion relationship optimized the specificity. For plasma samples, the inter-assay variability of this method was 6.4% (n = 79) and the intra-assay variability was 6.0% (n = 10). The variability for controls was 3.4% (n = 43). The profile of DAMGO amount versus time was determined in sheep plasma, and the corresponding pharmacokinetic data were calculated.

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.

A peripheral site of action for the attenuation of baroflex-mediated bradycardia by intravenous mu-opioid agonists

We previously reported that i.v. DAMGO (Tyr-D-Ala-Gly-NMePhe-Gly-ol), a selective mu-opioid agonist, causes an increase in blood pressure with no change in heart rate in unanesthetized sheep and subsequently demonstrated that DAMGO attenuates baroreflex-mediated bradycardia. To determine the site and mechanism by which mu-agonists inhibit baroreflex sensitivity, we have carried out further investigations by using DAMGO and another mu-agonist, DALDA (Tyr-D-Arg-Phe-Lys-NH2). The bradycardic response to norepinephrine (NE) was significantly blunted after i.v. DAMGO or DALDA in both nonpregnant and pregnant sheep. In contrast, the tachycardic response to sodium nitroprusside (SNP) remained unchanged in the presence of DAMGO or DALDA. In view of the highly restricted distribution of DALDA across the blood-brain barrier (BBB), we hypothesized that the blunting of reflex-mediated bradycardia by mu-opioid agonists can occur peripherally. Pretreatment with the quaternary opioid antagonist, naloxone methiodide (NM), completely blocked the attenuation of baroreflex sensitivity by DAMGO and DALDA in both nonpregnant and pregnant animals. These data suggest that in addition to central mechanisms, mu-opioid agonists can inhibit baroreflex sensitivity at a peripheral site, most likely by inhibiting vagal influence on heart-rate control rather than by acting directly at baroreceptors.

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

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 alpha and leptin and that the changes in tumor necrosis factor alpha and leptin concentrations during pregnancy continue to reflect changes in fat mass.

STUDY DESIGN

The levels of tumor necrosis factor alpha 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 alpha 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 alpha 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 alpha 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 alpha and leptin. The decrease in leptin reflects decreased fat accretion, and we speculate that the changes in tumor necrosis factor alpha may reflect a change in insulin resistance.

Cardiovascular responses of perimenopausal women to hormonal replacement therapy

OBJECTIVE

This study was undertake to test the hypothesis that hormone replacement therapy alters cardiovascular function during the first several months of therapy.

STUDY DESIGN

Serial estimates of blood pressure, heart rate, stroke volume, and venous capacitance were obtained before and at 1, 5, 9, and 21 weeks after the beginning of hormone replacement therapy with daily estradiol and intermittent norethindrone. Measurements were performed by means of electrocardiography, automated blood pressure measurement (Dynamap; Critikon Company LLC, Tampa, Fla), echocardiography, and plethysmography.

RESULTS

Hormone replacement therapy did not alter heart rate, blood pressure, or venous capacitance. End-diastolic volume and stroke volume were unchanged after 1 week of hormone replacement therapy but rose thereafter. After 5 weeks of hormone replacement end-diastolic volume and stroke volume were increased by 13 +/- 5 mL and 9 +/- 2 mL, respectively, and after 9 weeks the increases totaled 23 +/- 5 mL and 17 +/- 3 mL, respectively. As a result cardiac output rose progressively to a level 1.1 +/- 0.3 L/min (18%) greater than pretreatment values and systemic vascular resistance fell 15%. These changes were associated with a 3-fold increase in serum estradiol levels.

CONCLUSION

The studied regimen of hormone replacement therapy produces progressive cardiac remodeling and peripheral vasodilatation during the first 2 months of therapy.

Nuchal cord and neurodevelopmental performance at 1 year

OBJECTIVE

To test the null hypothesis that the presence of a nuchal cord at delivery has no effect on neurodevelopmental performance at 1 year of age.

METHODS

The offspring of 190 women with clinically normal antenatal courses were evaluated within 1 month of their first birthday by a blinded observer using the Bayley Scales of Infant Development. The cases were grouped based on the presence of a symptomatic nuchal cord during labor (abnormal fetal heart rate patterns or meconium), and significant differences were detected using analysis of variance.

RESULTS

A symptomatic nuchal cord was present during labor and delivery in 24% of the 190 cases. At 1 year of age scores on both Bayley scales were slightly but significantly (P < .01) lower in the offspring delivered with a symptomatic nuchal cord. The mental index was 116 +/- 9 versus 120 +/- 7, and the psychomotor index was 101 +/- 11 versus 107 +/- 9. These differences were accentuated (P = .09) when the symptomatic cases complicated by extreme tightness, multiple loops, or antenatal detection were compared to symptomatic cases without these additional complications (overall index 110 +/- 8 versus 105 +/- 10). There were no between group differences in multiple potential confounding obstetric or demographic variables.

CONCLUSIONS

These data do not support the null hypothesis and suggest that symptomatic nuchal cords, which are identified before labor as being extremely tight or having multiple loops, may be associated with a subclinical deficit in neurodevelopmental performance at 1 year of age.

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

OBJECTIVE

The objective of the study was to test the hypothesis that continuing regular exercise throughout pregnancy alters early neonatal behavior.

STUDY DESIGN

The 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.

RESULTS

The 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.

CONCLUSIONS

These data indicate that the neonates born of exercising mothers have a different neurobehavioral profile as early as the fifth day after birth.

Respiratory depression after intravenous administration of delta-selective opioid peptide analogs

We compared the effects of three micro-(DAMGO, DALDA, TNPO) and three delta-(DPDPE, DELT, SNC-80) opioid agonists on arterial blood gas after IV administration in awake sheep. None of the mu agonists altered pO2, pCO2 or pH. All three mu agonists decreased pO2 increased pCO2 and decreased pO2, and this effect was not sensitive to naloxone or TIPPpsi, a delta-antagonist, suggesting that it is not mediated by beta-opioid receptors. When administered to pregnant animals, there were significant changes in fetal pCO2 and pH. It may be possible to develop delta-selective opioid agonists which do not produce respiratory depression.

Cord blood leptin reflects fetal fat mass

OBJECTIVE

To explore the relationship between leptin levels and fat mass at the time of birth to test the hypothesis that the level of leptin in the fetal circulation is primarily an index of fetal fat mass.

METHODS

Leptin concentration was measured in cord blood obtained from the offspring of 42 women. Trimmed, drained placental weight and neonatal morphometrics were obtained after delivery.

RESULTS

The ranges in maternal weight (46.7-93.2 kg), weight gain (3.2-22.6 kg), percent body fat (10-34%), placental weight (290-688 g), birth weight (2.63-4.32 kg), neonatal fat mass (179-782 g), and cord blood leptin (1.7-26.7 ng/mL) were wide. The only morphometric variable that explained a significant portion of the variation in cord blood leptin levels was neonatal fat mass (r2 = 0.41), and this relationship was not significantly improved by best subset regression of additional fetal and placental morphometric variables (r2 = 0.46).

CONCLUSION

These data support the hypothesis and suggest that in the fetus, as in the child and the adult, fat mass is the major determinant of circulating leptin levels.

Effect of dietary carbohydrate on the glucose and insulin response to mixed caloric intake and exercise in both nonpregnant and pregnant women

The objective of this study was to test the hypothesis that a woman's dietary carbohydrate mix modifies the glucose and insulin response to both mixed caloric intake and exercise. Either a prospective randomized or a prospective randomized crossover design was used to examine the effects of two isocaloric, high-carbohydrate diets on the whole-blood glucose and insulin responses to mixed caloric intake and exercise in healthy nonpregnant (n = 14) and pregnant (n = 12) women. The diets differed only in the type of carbohydrate ingested. Those in one had low glycemic indexes and those in the other had high glycemic indexes. In nonpregnant women, the blood glucose response to a meal containing low-glycemic carbohydrate was half that seen with high-glycemic carbohydrate, and the effect of exercise on blood glucose was more pronounced while eating the high-glycemic carbohydrate diet. During pregnancy, women on the low-glycemic carbohydrate diet experienced no significant change in their glycemic response to mixed caloric intake, whereas those who switched to the high-glycemic carbohydrate diet experienced a 190% increase in their response. In conclusion, the type of dietary carbohydrate in a healthy, physically active woman's diet influences both her postprandial blood glucose profile and her blood sugar response to exercise.

Self-selected recreational exercise has no impact on early postpartum lactation-induced bone loss

Although exercise is known to positively impact bone mineral density (BMD), its effect on lactation-induced BMD loss has not been previously evaluated in a case-control study.

PURPOSE

The purpose of this study was to compare lactation-induced bone changes in women who engaged in regular, self-selected, recreational exercise versus those who refrained from such during early postpartum.

METHODS

Subjects were 20 healthy, lactating women who either exercised regularly (exercise, E; N = 11) or refrained from such (control, C; N = 9) during the first 3 months postpartum. Although preconception VO2max was significantly higher in E than C (E = 54.1, C = 36.9 mL.min-1.kg-1), no significant group differences were observed for parity, age, height, weight (WT), % body fat, dietary calcium intake, lactation calcium loss, and serum estradiol. Total body (TB), lumbar spine (LS), and femur neck (FN) BMD were measured within 2 wk of parturition and repeated at 3 months postpartum by dual energy x-ray absorptiometry.

RESULTS

Although TB was unchanged, BMD decreased significantly from baseline in both groups at LS (C = -5.4, E = -4.1%) and FN (C = -2.7, E = -2.8%). WT decreased significantly over time but was not significantly correlated with BMD loss. No significant group by time interactions were observed for WT or BMD changes.

CONCLUSION

These results suggest that regular, self-selected, recreational E has no impact on early postpartum lactation-induced BMD loss.

Baroreflex-mediated bradycardia but not tachycardia is blunted peripherally by intravenous mu-opioid agonists

OBJECTIVE

We sought to test the hypothesis that an intravenous dose of H-Tyr-D-Arg-Phe-Lys-NH2, a highly mu-receptor selective opioid peptide, suppresses baroreflex sensitivity through a peripheral mechanism.

STUDY DESIGN

A transient change in mean arterial pressure was produced in chronically instrumented pregnant ewes by norepinephrine or sodium nitroprusside in the absence or in the presence of H-Tyr-D-Arg-Phe-Lys-NH2, a highly mu-selective opioid peptide. In some studies naloxone methiodide, a peripheral opioid antagonist, was infused starting 60 minutes before the administration of H-Tyr-D-Arg-Phe-Lys-NH2 and maintained for a total of 90 minutes. Linear plots were obtained when the changes in mean arterial pressure during the pressure rise were plotted against the changes in heart rate and the sensitivity of the baroreflex was derived as the slope of the linear regression line.

RESULTS

We observed (1) lower baroreflex sensitivity after H-Tyr-D-Arg-Phe-Lys-NH2 administration with a hypertensive stimulus; (2) unchanged baroreflex sensitivity after H-Tyr-D-Arg-Phe-Lys-NH2 administration with a hypotensive stimulus; and (3) unchanged baroreflex sensitivity after H-Tyr-D-Arg-Phe-Lys-NH2 administration with a hypertensive stimulus in the presence of naloxone methiodide.

CONCLUSION

H-Tyr-D-Arg-Phe-Lys-NH2 suppresses the hypertensive but not the hypotensive arm of the baroreflex through peripheral opioid receptors. These results suggest that mu-opioid receptors are present in the vagus nerves and that the activation of these opioid receptors inhibits reflex bradycardia in pregnant sheep.

The one-year morphometric and neurodevelopmental outcome of the offspring of women who continued to exercise regularly throughout pregnancy

OBJECTIVE

Our purpose was to test the hypothesis that continuing regular exercise throughout pregnancy alters morphometric and neurodevelopmental outcome at 1 year.

STUDY DESIGN

The offspring of 52 women who exercised were compared with those of 52 control subjects who were similar in terms of multiple prenatal and postnatal variables known to influence outcome. All women were enrolled before pregnancy and had clinically normal antenatal and postnatal courses. Neurodevelopment was assessed by blinded examiners at 1 year of age, and morphometrics were obtained at birth and at 1 year of age.

RESULTS

At birth, the offspring of the exercising women weighed less (3.38 +/- 0.06 kg vs 3.58 +/- 0.07 kg) and had less body fat (9.5% +/- 0.8% vs 12.6% +/- 0.6%). However, at 1 year, all morphometric parameters were similar, and no clinically significant between-group differences were observed in performance on either the Bayley psychomotor (108 +/- 1 vs 101 +/- 2) or mental (120 +/- 1 vs 118 +/- 1) scales.

CONCLUSIONS

These data indicate that the offspring of exercising mothers have normal growth and development during the first year of life.

Cardiovascular and metabolic responses to two receptor-selective opioid agonists in pregnant sheep

OBJECTIVE

Our purpose was to assess the effects of an intravenous dose of a highly selective mu-(DALDA) and delta-(DPDPE) opioid peptide to determine which class of peptide has the best clinical potential.

STUDY DESIGN

Chronically instrumented pregnant ewes received a 0.3 mg/kg intravenous bolus of each peptide with and without opioid receptor blockade by means of a randomized prospective design.

RESULTS

Intravenous DALDA produced only mild hypertension and a loss of heart rate variability, whereas DPDPE produced respiratory depression, maternal hypertension, and a fall in heart rate in both mother and fetus. Uterine blood flow, oxygen uptake, and glucose uptake were unchanged with both drugs. The effects of DALDA but not DPDPE were reversed by opioid receptor blockade.

CONCLUSION

The delta-selective agonist had multiple nonopioid adverse effects, whereas the mu-selective agonist was well tolerated by the pregnant ewe, suggesting that mu-selective agonists have better potential for clinical use as an analgesic in pregnancy.

In vivo disposition of dermorphin analog (DALDA) in nonpregnant and pregnant sheep

Although synthetic opioid peptide analogs have been used extensively to study the functional roles of opioid receptors, little is known about their in vivo disposition. Our goal was to develop novel opioid drugs with limited transfer across the placenta. DALDA (Tyr-D-Arg-Phe-Lys-NH2) is a potent and highly selective mu agonist that is quite polar because of its 3+ charge at physiological pH. It can therefore be expected that the distribution of DALDA across the placenta would be highly restricted. In this study, we determined the pharmacokinetics and placental transfer of DALDA after systemic administration in sheep. DALDA was infused intravenously to four nonpregnant and four pregnant sheep at a dose of 0.6 mg/kg/hr for 4 hr. Steady state plasma levels of DALDA were 5436 +/- 464 ng/ml in nonpregnant sheep and 5214 +/- 661 ng/ml in pregnant sheep. A one-compartment open model provided an excellent fit for nonpregnant and pregnant plasma data. The apparent volume of distribution was estimated to be 45.6 +/- 4.4 and 59.2 +/- 7.9 ml/kg in nonpregnant and pregnant animals, respectively. There was no difference in the elimination half-life of DALDA in nonpregnant (1.4 +/- 0.1 hr) and pregnant (1.7 +/- 0.2 hr) animals, and clearance was also similar in nonpregnant (23.1 +/- 1.7 ml/kg/hr) and pregnant (23.7 +/- 1.3 ml/kg/hr) animals. These data suggest that the distribution of DALDA is restricted to plasma volume and that its disposition is not altered in pregnancy. DALDA was not detected in any of the fetal plasma samples (< 50 ng/ml), indicating that fetal plasma concentration is < 1% of maternal concentration. The highly restricted placental distribution of DALDA suggests that it may be a promising opioid drug for obstetrical use.

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.

Effects of maternal exercise on fetal activity in late gestation

In order to test the effects of maternal exercise in late gestation on fetal biophysical activities as measured by fetal breathing, shoulder movement, and kick response, these parameters were monitored by ultrasound in ten healthy pregnant women at 35 weeks of gestation before and after 20 minutes of aerobic dance and before and after 20 minutes of rest. A randomized crossover design between exercise (sequence A) and rest (sequence B) that used each pregnant woman as her own control was used in this study. Cumulative means for each fetal activity were compared. Results indicated a significant decrease in fetal breathing after maternal exercise and no significant change in shoulder movements or kick response.

Morphometric and neurodevelopmental outcome at age five years of the offspring of women who continued to exercise regularly throughout pregnancy

OBJECTIVE

To test the hypothesis that continuing regular, vigorous, sustained exercise throughout pregnancy adversely affects morphometric and neurodevelopmental outcome in offspring at 5 years of age.

STUDY DESIGN

The offspring of 20 women who exercised were compared with those of 20 physically active control subjects. The women and their offspring were matched for multiple prenatal and postnatal variables known to influence outcome. All women were enrolled before the index pregnancy, monitored throughout, and had clinically normal antenatal, intrapartum, and postnatal courses. Morphometric measures were obtained at birth and at 5 years of age by a single, trained observer. Neurodevelopment was assessed by developmental psychologists masked to maternal exercise status. Data were analyzed with an unpaired Student t test.

RESULTS

At birth, head circumference and length were similar, but the offspring of the exercising women weighed less (3.40 +/- 0.80 vs 3.64 +/- 0.70 kg) and had less fat (10.5% +/- 0.9% vs 15.1% +/- 0.6%). At 5 years of age, head circumference and height were similar, but the offspring of the women who exercised weighed less (18.0 +/- 0.5 vs 19.5 +/- 0.6 kg) and had a lower sum (sigma) of five site skinfolds (37 +/- 1 vs 44 +/- 2 mm). Motor, integrative, and academic readiness skills were similar. However, the exercise offspring performed significantly better on the Wechsler scales (125 +/- 2 vs 116 +/- 3) and tests of oral language skills (119 +/- 2 vs 109 +/- 3).

CONCLUSIONS

These data refute the hypothesis and suggest that exercise during pregnancy reduces the subcutaneous fat mass of the offspring.

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.

The effects of maternal aerobic exercise on human placental development: placental volumetric composition and surface areas

The histomorphometry of term placentae from women who exercised regularly throughout either the first half or all of pregnancy was compared to that of placentae from matched controls to determine if regular exercise during pregnancy produced histomorphometric evidence of altered development and transport capacity. Conventional stereological techniques were used to estimate placental volumetric composition, surface areas, and villous and vascular configurations in the three groups. Exercise confined to early pregnancy increased the parenchymal component of the placenta, total vascular volume and site-specific capillary volume and surface area. Exercise throughout pregnancy increased these and multiple other histomorphometric parameters associated with the rate of placental perfusion and transfer function. However, significant changes were confined to villi > 80 microns in diameter. The localization of both the timing of the stimulus and the anatomical sites affected indicates that regular, sustained exercise modifies placental development primarily in early and mid-pregnancy. We speculate that the lack of significant changes in the structure and configuration of the smaller villi indicates that other adaptive mechanisms, such as increased rates of placental blood flow, must be well developed by the latter portion of the mid-trimester and adequately maintain fetal oxygenation and substrate delivery throughout the third trimester.

Effect of recreational exercise on pregnancy weight gain and subcutaneous fat deposition

This study was designed to test the hypothesis that continuing a regular regimen of recreational endurance exercise alters the time-specific rate of maternal weight gain and subcutaneous fat deposition during pregnancy. Serial measurements of body mass and 5-site skinfold thickness were obtained from 44 women before and during pregnancy who continued their preconceptional exercise regimen throughout pregnancy and from women who voluntarily stopped their preconceptional exercise regimen either before conception (N = 31) or reduced it below baseline fitness levels in very early pregnancy (N = 4). In the first and second trimester, the rate of weight gain and change in skinfold thicknesses were unrelated to exercise performance. However, those who continued exercise had a reduced rate of weight gain and change in skinfold thickness at specific sites in the last trimester of pregnancy. Overall weight gains were (mean +/- SEM) 13.0 +/- 0.5 kg and 16.3 +/- 0.7 kg in the exercise and control groups, respectively, and the increases in the sum of skinfolds were 22 +/- 2 mm and 31 +/- 2 mm, respectively. We conclude that continuing a regular exercise regimen throughout pregnancy does not influence the rate of early pregnancy weight gain or subcutaneous fat deposition but decreases both in late pregnancy. However, overall pregnancy weight gain remains well within the normal range.

Second-trimester placental volumes predict birth weight at term

OBJECTIVE

To test the hypothesis that second-trimester placental growth is a major determinant of size at birth in healthy, active women.

METHODS

Three serial measurements of fetal morphometry and placental volume were obtained between the 14th and 26th weeks of an accurately dated singleton pregnancy in 40 subjects.

RESULTS

Second-trimester placental volumes were variable, increasing from (mean +/- standard deviation) 130 +/- 35 to 248 +/- 67 and to 375 +/- 92 cm3 at 16, 20, and 24 weeks, with an average growth rate of 31 +/- 8 cm3/weeks. At delivery, fresh placental volumes and birth weights were also variable, ranging between 304-823 cm3 and 2.6-4.4 kg, respectively. Significant correlations (r > 0.79) were present between second-trimester placental volume or growth rate and placental volume at delivery and birth weight, corrected for gestational age and infant sex. However, correlations between second-trimester fetal biometry and both corrected birth weight and birth weight percentile were poor (r < 0.45).

CONCLUSION

Second-trimester placental volumes and growth rates are good predictors of size at birth in healthy, active women. We speculate that this technique may have real value as an early screening tool to identify cases at risk of anomalous third-trimester growth.

The physiological response of instructors and participants to three aerobics regimens

This study was designed to test the hypothesis that there are regimen-specific differences in the thermal, metabolic, and cardiovascular responses of nonpregnant women when they perform their chosen type of aerobics at their usual performance level. Thirty-six instructors and 53 participants were studied while performing their chosen aerobics regimen under simulated field conditions using oxygen consumption as the index of exercise intensity. Under these conditions no significant differences were observed in the physiological response to low impact, high impact, or step regimens. However, although their ratings of perceived exertion were lower, the participants worked at a much higher exercise intensity than the instructors (76 +/- 1 vs 62 +/- 2% VO2max). As a result they attained a higher respiratory exchange ratio (0.96 vs 0.90), rectal temperature (38.62 vs 38.12 degrees C), and blood levels of glucose (5.70 vs 4.95 mmol.l-1), lactate (3.65 vs 1.60 mmol.l-1), and norepinephrine (2656 vs 1191 pg.ml-1). We conclude that both intensity and physiological response to aerobics are individual specific not regimen specific and that participants consistently underestimate their level of performance.

A clinical approach to exercise during pregnancy

Our knowledge is limited and there are serious theoretic concerns about combining a vigorous exercise regimen with pregnancy. The outcome data available, however, suggest that a healthy woman may begin or maintain a regular exercise regimen during pregnancy with benefit and without adversely affecting the course and outcome of the pregnancy. The data also suggest that the clear difference between theoretic concern and observed outcome is best explained by the hypothesis that the physiologic adaptations to exercise and to pregnancy are complimentary and feto-protective. Although the upper level of safe performance is not established, it appears that the otherwise healthy mother-to-be can obtain the benefits of a regular exercise regimen without undue risk to the embryo and fetus. The exact regimen can be flexible and individualized, provided that both the exercise and the pregnancy are monitored. In February 1994, a new set of guidelines for exercise during pregnancy and the postpartum period was published by the American College of Obstetricians and Gynecologists. These guidelines are more liberal than those mentioned previously. Interested parties should write to the American College of Obstetricians and Gynecologists, 409 12th Street S.W., Washington, DC 20024-2188 and ask for technical bulletin no. 189.

The effect of sustained exercise on follicular phase levels of 17 beta-estradiol in recreational athletes

OBJECTIVE

Our purpose was to test the hypothesis that sustained exercise elevates circulating levels of 17 beta-estradiol in an intensity-dependent manner.

STUDY DESIGN

Blood samples were obtained in the follicular phase of the menstrual cycle from 75 female recreational athletes before and immediately after 20 minutes of aerobics or running at their usual exercise intensity.

RESULTS

The levels of 17 beta-estradiol rose after exercise 97% of the time. At exercise intensities between 50% and 88% of maximum capacity there was a direct linear relationship (r = 0.57) between exercise intensity and magnitude of increase in estradiol levels. A similar relationship was not present for cortisol.

CONCLUSION

Sustained exercise produces an intensity-dependent increase in the levels of 17 beta-estradiol that probably reflects decreased hepatic clearance caused by the fall in splanchnic blood flow. Thus the magnitude of the increase in the level of 17 beta-estradiol can be used as a rough index of the exercise-induced decrease in splanchnic blood flow.

Fetal heart rate response to sustained recreational exercise

OBJECTIVE

We aimed to test the hypotheses that fetal heart rate increases during and after sustained exercise and that the magnitude of the increases is related to gestational age and the duration, intensity, and type of exercise.

STUDY DESIGN

Maternal oxygen uptake and fetal heart rate were monitored in 120 regularly exercising women in association with routine 20-minute workouts between 16 and 39 weeks' gestation.

RESULTS

In 97% of the studies fetal heart rate increased during and after exercise. This was significant at all gestational ages and with all forms of exercise with an overall increase of 15 +/- 11 beats.min-1 at 60% +/- 12% of maximal aerobic capacity (mean +/- SD). The magnitude increased with gestational age (10 +/- 8 to 20 +/- 11 beats.min-1), exercise intensity (8 +/- 7 to 21 +/- 13 beats.min-1), and exercise duration (8 +/- 4 to 16 +/- 7 beats.min-1).

CONCLUSION

We concluded that the hypothesis is correct and speculate that these changes represent a maturing fetal response to a reduction in Po2.

Effect of recreational exercise on midtrimester placental growth

OBJECTIVE

The purpose of our study was to test the hypothesis that regular recreational exercise increases the rate of growth in placental volume in the midtrimester of human pregnancy.

STUDY DESIGN

Serial measurements of placental volume were obtained between the fourteenth and twenty-sixth gestational week in 18 subjects who exercised regularly throughout the midtrimester and in 16 matched controls with an ultrasonographic system equipped with a fixed-base, articulated-arm, 3.5 MHz B-mode transducer.

RESULTS

Placental volumes were significantly greater in the women who maintained a regular exercise regimen throughout the midtrimester. At 16 weeks (mean +/- SD) volumes were 141 +/- 34 cm3 and 106 +/- 18 cm3 in the two groups. This difference increased at 20 weeks (265 +/- 67 cm3 vs 186 +/- 46 cm3) and again at 24 (410 +/- 87 cm3 vs 270 +/- 58 cm3) weeks' gestation because of a significant between-group difference in the rate of growth in placental volume over this time interval (34 +/- 8 cm3/wk vs 21 +/- cm3/wk).

CONCLUSION

We conclude that the hypothesis is correct and speculate that the change in growth rate represents an adaptive response to the intermittent stimulus of a reduction in regional blood flow.

The changing glycemic response to exercise during pregnancy

This study was designed to test the hypothesis that pregnancy reverses the nonpregnant hyperglycemic response to sustained exercise. Serial data were obtained from 75 exercising women. Before pregnancy, exercise produced an intensity-dependent increase in blood glucose that averaged 1.5 mmol/L at high intensities. By the eighth week this response was blunted and blood glucose increased only when exercise intensity exceeded 80% of maximum. At 15 weeks this progressed and was not associated with a change in either the insulin or catecholamine response. By the twenty-third week exercise produced a decrease in blood glucose that was no longer related to exercise intensity. We conclude that the hypothesis is correct and speculate that the early change in the response is related to decreased hepatic glucose release coupled with increased glucose oxidation. In late pregnancy this is probably accentuated by fetoplacental demands.

The changing thermal response to endurance exercise during pregnancy

This study was designed to test the hypothesis that the thermal response to endurance exercise is altered by the thermal adaptations to pregnancy. Accordingly, rectal temperature was monitored in 18 recreational athletes before, during, and after 20 minutes of continuous exercise before conception and every 6 to 8 weeks during pregnancy. Mean exercise intensity was 64% of VO2 max before conception and did not change during pregnancy. However, the peak rectal temperature reached during exercise decreased by 0.3 degrees C at 8 weeks and then fell at a rate of 0.1 degrees C per lunar month through the thirty-seventh week. This appeared to be related to changes in resting temperature, thermal mass, sweating threshold, and venous capacitance that began early in pregnancy. These data suggest that the magnitude of any exercise-associated thermal stress for the embryo and fetus is markedly reduced by the maternal physiologic adaptations to pregnancy.

The VO2max of recreational athletes before and after pregnancy

This study was designed to test the hypothesis that pregnancy has an added training effect (increases "absolute" VO2max) in well-conditioned, recreational athletes. VO2max was measured serially in 20 nonpregnant recreational athletes who maintained their exercise within +/- 10% of initial levels over a 15-month period and 20 similar women who conceived and continued exercise at a reduced level during pregnancy with a return to within 20% of initial levels by 12 wk postpartum. Initially the two groups were similar in terms of age (30 +/- 1 vs 30 +/- 2 yr), weight 57.6 +/- 7.2 vs 59.7 +/- 7.5 kg), max pulse rate (189 +/- 8 vs 187 +/- 10 bpm), and absolute (3083 +/- 469 vs 3138 +/- 464 ml.min-1) VO2max. In the nonpregnant group the values obtained 15 months later were unchanged (weight = 57.8 +/- 6.6 kg, max pulse = 191 +/- 7 bpm, VO2max = 2977 +/- 397 ml.min-1) while those who conceived had a significant increase in absolute VO2max that was evident 12-20 wk postpartum and was maintained at the time of final testing 36-44 wk postpartum (3368 +/- 435 ml.min-1). Both weight (60.1 +/- 8.1 kg) and maximum pulse rate (185 +/- 12 bpm) were unchanged. These data indicate that pregnancy is followed by a small but significant increase in VO2max in recreational athletes who maintain a moderate to high level of exercise performance during and after pregnancy.

When do cardiovascular parameters return to their preconception values?

To determine if the postpartum period is reflective of a woman's cardiovascular status before pregnancy, we performed serial studies of 13 women before conception and at 6 and 12 weeks post partum. All pregnancies were singleton without hypertensive complications. Cardiac output, stroke volume, and end-diastolic volume were calculated with M-mode echocardiography from the left ventricular dimensions with subjects in the left lateral position. Systemic vascular resistance was calculated from cardiac output and simultaneous measurements of blood pressure. Stroke volume and end-diastolic volume remained consistently elevated over preconception values at 6 and 12 weeks. Systemic vascular resistance remained decreased, compared with baseline, at 12 weeks. Thus cardiovascular parameters had not returned to the preconception baseline, and previous studies that have used this time period for comparison have underestimated the contribution of stroke volume to the total change in cardiac output during pregnancy.