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.

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.

Ovine placental cortisol production.

Cortisol levels were determined by radioimmunoassay in samples simultaneously obtained from the four vessels serving the ovine placenta (uterine artery and vein, umbilical artery and vein). These samples were collected daily over a 20- to 30-day interval in three animals in the latter third of pregnancy. Cortisol levels in the uterine and umbilical veins were higher than those in the arteries in 67 of 73 sample sets. Net synthesis of 11-deoxycortisol and cortisol from 17 alpha-hydroxyprogesterone by dispersed placental cells was also demonstrated in vitro. These data provide strong evidence that the ovine placenta has the ability to synthesize 11-deoxycortisol and cortisol in vitro and normally does so in vivo.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Endurance exercise and pregnancy outcome.

The interaction between maternal endurance exercise at or above a minimal conditioning level, prior to and during pregnancy, and pregnancy outcome was examined prospectively in our obstetrical populace using epidemiologic techniques. Over a 3-month interval all women registering for antepartum care were interviewed. Those planning to continue exercise during pregnancy were re-interviewed between the 28th and 34th gestational weeks. A detailed review of clinical records was used for outcome assessment. Women who continued endurance exercise at or near preconceptual levels during pregnancy gained less weight (-4.6 kg), delivered earlier (-8 d), and had lighter-weight offspring (-500 g) than those who stopped exercising prior to the 28th week. The latter group gained 2.2 kg more weight but delivered similar birthweight infants at a similar gestational age as their sedentary controls.

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

UNLABELLED: 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.

Thermoregulatory and metabolic responses to jogging prior to and during pregnancy.

Ten joggers were serially studied prior to and during pregnancy at their individual training intensity levels to estimate their thermal and metabolic response to exercise in the field. Prior to conception, a 20-min run at 74% of VO2max (range = 62 to 90%) increased the respiratory exchange ratio to 0.90 +/- 0.01 (range = 0.87 to 0.96) with a rise in whole blood glucose (5.19 +/- 0.14 to 6.63 +/- 0.23 mM X l-1), lactate (0.61 +/- 0.06 to 2.62 +/- 0.74 mM X l-1), and rectal temperature (37.5 +/- 0.1 to 39.0 +/- 0.1 degree C). Despite a spontaneous decrease in exercise intensity to 57 +/- 5% of VO2max (range = 34 to 79%) at 20 and to 47 +/- 2% of VO2max (range = 36 to 59%) at 32 wk gestation, the rise in respiratory exchange ratio with exercise was maintained at 0.92 +/- 0.02 (range = 0.88 to 0.97) and 0.93 +/- 0.01 (range = 0.88 to 0.97), respectively, suggesting a shift to the left in the relationship between exercise intensity and fractional carbohydrate utilization by muscle during exercise in pregnancy. The concomitant changes in whole blood glucose before and after exercise at 20 (4.46 +/- 0.16 to 4.45 +/- 0.08 mM X l-1) and 32 (5.30 +/- 0.19 to 4.55 +/- 0.15 mM X l-1) wk further strengthen this view. Post-exercise, whole blood lactate levels at 20 (0.53 +/- 0.06 to 1.59 +/- 0.30 mM X l-1) and 32 (0.77 +/- 0.07 to 0.89 +/- 0.11 mM X l-1) wk were lower than those observed prior to pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of betamethasone and timed delivery in management of premature rupture of the membranes in the preterm pregnancy.

Of 43 women admitted with premature rupture of the membranes between 27 and 32 weeks' gestation, 27 received antepartum glucocorticoid with delivery timed to occur approximately 24 hours after the first dose of steriod. Sixteen patients did not receive glucocorticoid and were managed expectantly. Neonatal mortality was significantly less in the steroid group (15% vs. 50%, p less than .01), and this difference was explained by a reduction in deaths from respiratory distress syndrome. Rates of infectious morbidity for both mothers and infants were similar between the steroid-treated group and the group managed expectantly.

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.