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

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Abstract

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.

Introduction

The interactions amongst maternal exercise, fetal oxygenation and feto-placental growth are complex because the effects of exercise on the maternal physiological parameters of interest (placental bed blood flow and arterial blood sugar and oxygen content) vary with the type, frequency, duration and intensity of the exercise as well as the physical fitness of the mother and the time point in the pregnancy when the exercise is carried out [1], [2], [3], [4], [5], [6]. The goal of this paper is to review what is known about these interactions and both their short- and long-term effects on the growth and development of the offspring. But first, to provide essential background information, current concepts of nutrient and oxygen availability as regulators of feto-placental growth will be reviewed.

Section snippets

Nutrient and oxygen as regulators of feto-placental growth

Although much of the conceptual data has been generated in animal models [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], this discussion will focus on the human because the growth rate of the human feto-placental unit is less sensitive to decremental changes in overall nutrient and oxygen availability [18], [19], [20]. In the human, the slow velocity of fetal growth and the improved maternal energy efficiency and perfusion balance which occur when nutrient and/or oxygen availability is

The effects of maternal exercise on placental bed blood flow

Sustained bouts of maternal exercise have both acute and chronic effects on placental bed blood flow. During the exercise blood flow is diverted away from the viscera to the exercising muscle and skin [5], [6]. The magnitude of the reduction in flow is directly proportional to exercise intensity and the muscle mass used (which varies with the type of exercise), and with common types of exercise performed at usual exercise intensities, the reduction usually exceeds 50%. This exercise-induced

The effects of maternal exercise on glucose and oxygen delivery

Prior to pregnancy, sustained weight-bearing exercise increases glucose oxidation while exercise-associated sympathetic responses mobilize glucose stores and stimulate gluconeogenesis. The end result is that blood glucose levels rise for at least the first hour unless the exercise intensity is extremely high [2]. During pregnancy however, sympathetic responses are blunted and both glucose oxidation and lipogenesis are increased [2], [4]. As a result, sustained, weight-bearing exercise at usual

The effects of exercise on feto-placental growth and size at birth

There is no question that a sustained bout of weight-bearing exercise during pregnancy causes an acute reduction in oxygen and nutrient delivery to the placental site, and in sedentary women, the reduction in oxygen delivery is occasionally is severe enough to produce fetal bradycardia. However, when women continue regular bouts of sustained, weight-bearing exercise during pregnancy it increases maternal (and perhaps fetal) plasma volume, intervillous space blood volume, cardiac output and

The effects of specific exercise regimens on feto-placental growth and size at birth

Ii is important to point out that many exercise regimens designed for and marketed to pregnant women through various organizations are unstudied. Nonetheless, numerous investigators have been interested in the effects of exercise on birth weight and the following paragraphs summarize their work.

Numerous investigators have reported that continuing sustained weight-bearing exercise at reduced levels during pregnancy has no discernable effect on birth weight (placental data and other morphometric

The modifying effect of an exercising woman’s diet on feto-placental growth and size at birth

There is one other variable which modifies the effect of exercise on feto-placental growth: the type of carbohydrate eaten by the mother [17]. The infants born of women who eat carbohydrates which elevate 24 h blood glucose levels are symmetrically large at birth irrespective of exercise performance (mean weight=4170 g, length=53.1 cm) and have large placentas (550 g) as well, while the infants born of women who eat carbohydrates which keep maternal blood sugars in the nonpregnant range weigh

The effect of exercise on post-natal growth and development

The information on this topic is extremely limited and comes from only one laboratory [4], [42], [43]. To date, only two types of exercise regimens have been studied. The offspring of women who continue rigorous weight-bearing exercise regimens throughout pregnancy demonstrate signs of improved attentiveness and behavioral control in the immediate neonatal period, maintain the same morphometric profile (normal axial growth with reduced weight and fat mass) at age 5, and are neurodevelopmentally

Conclusions

During sustained forms of exercise uterine blood flow falls and with it oxygen and glucose delivery to the placental site and fetal pO2. However, experimental evidence indicates that a variety of exercise-induced adaptations coupled with concurrent physiological changes maintain utero-placental-fetal oxygenation at normal levels in healthy physically-active women with clinically normal singleton pregnancies who exercise at sea level. Neurodevelopmental findings also support this conclusion. The

Condensation

Maternal exercise during an uncomplicated pregnancy does not produce significant fetal hypoxia, improves placental growth and function, and has variable effects on fetal growth depending on the time in pregnancy when the exercise is carried out and the type, frequency, intensity and duration of the exercise regimen.

Acknowledgements

This work and the experiments discussed within were supported by Grants #HD21268, #HD21109 and #RR00080 from the National Institute of Child Health and Human Development and funds from MetroHealth Medical Center. Invaluable experimental assistance was provided by Beth Lopez, Susan Ridzon, Stephanie Schmidt, and Kristin Petry.

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