Exercise and pregnancy

Exercise and pregnancy

Authors By Aly Abdulla BSc, MD, LMCC, CCFP(c), DipsportMed and Faiza Abdulla CDA During my tenure as a sports medicine specialist, I have been approached by many women who would either like to continue exercising during their pregnancy or begin an exercise programme at this juncture in their lives. There are many physiological changes during pregnancy that need to be understood to ensure a safe exercise prescription. Once these changes and appropriate recommendations are instituted, then the risks to the developing fetus and the pregnant mother are ameliorated. We will review the physiologic changes during pregnancy and their impact on the foetus, the contraindications to exercise, the benefits of exercise to pregnancy and labour, and the recommendations for exercise prescription by the American College of Obstetricians and Gynecologists (ACOG)⁽¹⁾. Physiologic Changes of Pregnancy Hemodynamic Exercise acts in concert with pregnancy to increase both heart rate and stroke volume, therefore increasing cardiac output ⁽²⁾. Stroke volume is the more important factor and it is caused by an increase in plasma volume. However, during exercise, blood is diverted from abdominal viscera, including the uterus, to supply exercising muscle. This decrease in splanchnic blood flow can reach 50 percent and raises theoretic concerns about fetal hypoxemia ^(3,4). Maternal body position also affects cardiac output during pregnancy. After the first trimester, the supine position and prolonged standing is associated with a decrease in cardiac output ⁽⁵⁾. The reduction in venous return in the supine position is secondary to uterine compression and can be ameliorated by assuming a right or left sided lying position. Prolonged standing leads to increased peripheral pooling. Certain recommendations will be made below.		Oxygen Needs Pregnancy causes a decrease in functional reserve capacity; while tidal volume and oxygen consumption are increased ⁽⁶⁾. With mild exertion, pregnant women have a greater increase than their non-pregnant counterparts in respiratory frequency and oxygen consumption to meet their greater oxygen demand. As exercise increases to moderate and maximal levels, however, pregnant women demonstrate decreased respiratory frequency and maximal oxygen consumption. The oxygen demand at high levels of activity appears to overwhelm the system. This may be partially due to the obstructive effect of an enlarged uterus on diaphragmatic movement ⁽⁷⁾. The issue of theoretical fetal hypoxemia is again raised. Energy Needs Pregnancy and exercise are associated with a higher need for energy. In the first two trimesters, an increased intake of 150 calories per day is recommended; an increase of 300 calories per day is required in the third trimester ⁽⁸⁾. Caloric needs with exercise are even higher. The competing energy needs of the exercising mother and the growing fetus raise the theoretical concern that excessive exercise might adversely affect fetal development. Maternal and Foetal Temperature Issues The metabolic rate increases during both exercise and pregnancy, resulting in greater heat production. Theoretically, when exercise and pregnancy are combined, a rise in maternal core temperature could decrease fetal heat dissipation to the mother. Animal studies have demonstrated that an increase in core temperature can lead to midline fusion defects of the central nervous system ⁽⁹⁾. Hormonal Changes Artal et al have brought up the theoretical concerns about premature labour in women who exercise in late pregnancy ⁽¹⁰⁾. Exercise is known to increase circulating levels of norepinephrine and epinephrine ⁽¹⁰⁾. Norepinephrine has been shown to increase both the strength and the frequency of uterine contractions. In contrast, epinephrine has an

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