Exercise Considerations Before, During, and After Pregnancy

Introduction

Over the past decade, there has been an increased interest in the topic of physical activity during pregnancy. This is likely due to the increasing number of studies that have shown what benefits exercise can have during this unique time in a woman's life. Physicians and patients often express uncertainty regarding physical activity during pregnancy out of concern for the safety of both the mother and fetus. Previous studies have shown that physical activity is not associated with critical outcomes such as miscarriage, neonatal death, preterm birth, or birth defects. The dramatic rise in obesity, hypertension, and diabetes over the past few decades is well-documented in the literature. Subsequently there has been a similar increase in pregnancy complications such as gestational diabetes, gestational hypertension, and preeclamspsia. For this reason, there is an emphasis on using physical activity to help decrease the risk of these complications and optimize maternal-fetal health during pregnancy.

Pregnancy no longer needs to be thought of as a time to cease all activity, and it is important to counsel patients that there can be more complications by not exercising. Exercise throughout all three trimesters of pregnancy is safe, does not lead to an increase in major complications, and improves overall pregnancy outcomes. While the benefits almost always outweigh the risks for the general pregnant population, it is important to be aware of contraindications and to know when to refrain from certain activities. The goal of this chapter is to discuss the specific considerations and recommendations for exercise during pregnancy and the peripartum period based on the most updated guidelines, explain how the physiologic changes throughout pregnancy may impact the ability to perform physical activity, and describe appropriate precautions to take before engaging in physical activity.

Pathophysiology

Pregnancy has a profound effect on multiple body systems, and the subsequent physiologic adaptations can be a large factor in determining the level of participation in physical activity for a pregnant woman. In the section, we will discuss the relevant adaptations and physiologic changes during pregnancy.

Anatomic/Musculoskeletal Considerations

There are various anatomic changes that occur throughout pregnancy that may affect a woman's ability to participate in certain activities or sports, of which the most obvious and noticeable is gestational weight gain. For a female with a normal prepregnancy body mass index (BMI) (18.5–24.9 kg/m ² ), the optimal weight gain is between 25 and 35 pounds, with an average of 1 pound per week in the second and third trimesters. Increased mass may transfer significant force across the larger weight-bearing joints such as the knees and hips. Over time, this may cause discomfort and limit the ability to participate in activities or sports requiring full load bearing, such as running.

Throughout pregnancy, both the expanding uterus and enlarging breasts will displace the center of gravity. Increased lumbar lordosis and subsequent anterior pelvic rotation on the femur occur in pregnancy, changing a woman's center of gravity. This is important for activities that require optimal balance such as cycling on a nonstationary bike or walking on uneven ground.

Finally, ligamentous laxity increases throughout pregnancy, secondary to the effects of increased levels of estrogen and relaxin, which can predispose a female to joint instability and the theoretic risk of increased strains and sprains. ^, ^,

Hemodynamic Adaptations

Significant hemodynamic changes occur during pregnancy, including increased cardiac output, increased resting heart rate, increased stroke volume, and decreased systemic vascular resistance. ^, Cardiac output may increase by as much as 50% in the third trimester. ^, These changes are to supply sufficient blood to the placenta and the growing fetus. ^, During exercise, there can be up to a 50% decrease in splanchnic blood flow and subsequently blood flow to the uterus, as blood is redirected to the exercising muscles. This raises the hypothetical risk of fetal hypoxemia during exercise, which has been the subject of multiple reports. However, flow velocity profiles in the fetal aorta and umbilical circulation in various studies resulted in contradictory and inconclusive results. ^, ^, At this time, the general consensus is that an increase in fetal heart rate between 10 and 30 beats per minute (bpm) over baseline during maternal exercise does not have a negative sequela on the fetus and that overall fetal injuries are unlikely during a normal uncomplicated pregnancy.

An important consideration is the effect of supine positioning on the fetus, both at rest and during exercise. Primarily after the first trimester, compression of the inferior vena cava by the enlarged uterus reduces cardiac output. ^, A similar phenomenon has been seen with motionless standing for prolonged periods, which leads to decreased venous return and a subsequent increased risk of hypotension. For this reason, it is best to assume a right or left lateral side lying position and avoid motionless standing as pregnancy progresses, especially if one is experiencing hypotensive episodes. Equally important is avoiding supine exercises such as bench press or sit-ups.

Respiratory Adaptations

Along with the cardiovascular adaptations during pregnancy, significant respiratory changes occur. As the uterus enlarges, the diaphragm displaces superiorly, which ultimately causes a profound increase in tidal volume and subsequently minute ventilation, decreasing arterial carbon dioxide. ^, ^, All these adaptations protect the fetus from an acidic environment, which may significantly affect the function of various organ systems, such as the cardiovascular and central nervous systems, ultimately lowering APGAR (appearance, pulse, grimace, activity, and respiration) scores.

The pressure of the enlarged uterus on the diaphragm causes a decrease in oxygen availability and thereby increased work of breathing and feelings of respiratory discomfort late in pregnancy. ^, In response to increased oxygen requirements of the fetus, there are mild increases in tidal volume and oxygen consumption in pregnant women. To meet the greater oxygen demand during physical activity, pregnant women will have an increase in respiratory frequency and oxygen consumption with just mild exercise. ^, ^, ^, Studies have demonstrated that during pregnancy, the subjective effort to perform aerobic exercise is increased and maximum voluntary exercise performance is decreased. ^, ^,

Thermoregulatory Adaptations

Metabolic rate increases throughout pregnancy subsequently increasing heat production. ^, In the first trimester, core temperatures above 39°C (103°F) should be avoided because of an increased risk of neural tube defects. ^, ^, In the second and third trimesters, thermoregulatory control improves, during which fetal temperature is maintained approximately 1°C above maternal core temperature, due to fetoplacental metabolism. ^, ^, Core temperature does not increase significantly with steady-state moderate exercise, which is approximately 60%–70% V o ₂ max. ^, It is critical that heat dissipation remains greater than heat production to protect the fetus and ensure adequate uterine blood flow. For this reason, exercising in hot, humid environments or engaging in strenuous and high-intensity activities should be avoided.

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