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How do common diseases and their treatment impact on pregnancy?
How might pregnancy impact on common illness?
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Although women of childbearing age represent a younger and generally healthy population, currently 40% of women entering pregnancy have chronic medical conditions. The rise in the rates of obesity and type 2 diabetes, combined with modern medical technology, have resulted in pregnancy in older and sicker women. It is important to consider how diseases and their treatment may impact pregnancy and how pregnancy may affect certain diseases. This chapter will focus on the most common medical problems in pregnancy.
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During pregnancy, blood volume and cardiac output rise, and systemic vascular resistance decreases. Later in pregnancy the gravid uterus may compress the inferior vena cava, thereby significantly decreasing preload in the supine position. Cardiac output increases 40% by mid-pregnancy until labor and delivery when it increases further. Increased blood volume and left atrial dimensions may contribute to the increase in palpitations and supraventricular tachycardia. If the heart is damaged either by congenital heart disease or by cardiomyopathy, the increase in cardiac work cannot occur as effectively. In addition, just after delivery, with a uterine contraction a liter of blood can be shunted from the uterus into the general circulation. Cardiac lesions associated with a fixed cardiac output will not tolerate this sudden increase in volume. Hence, the most common complications in late pregnancy or immediately after delivery include pulmonary edema and, less commonly, right heart failure. In addition, the risk of a fetus developing congenital heart disease is increased if the mother has the same problem (for example, 1:4 in tetralogy of Fallot and 1:15 in atrial septal defects). Patients with severe pulmonary hypertension and/or Eisenmenger syndrome characterized by a reversed right-to-left shunt have increased mortality rates, especially during the first 48–72 hours postpartum.
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Systemic vascular resistance decreases about 25%, which may improve any cardiac condition that benefits from after-load reduction such as aortic insufficiency. When compression of the inferior vena cava decreases venous return to the heart, patients with preload-dependent cardiac conditions such as aortic stenosis or poor left ventricular function may experience hypotension, especially when supine. Because the increased cardiac demands peak at 24 to 28 weeks of gestation, cardiac decompensation may become evident at the end of the second trimester.
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Labor and delivery may be associated with cardiac decompensation when one to two units of blood leave the uteroplacental circulation during contraction. When the contraction ceases, the blood returns to the uteroplacental circulation.
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Patients with peripartum cardiomyopathy that occurs in the third trimester and up to six months following delivery have symptoms and signs consistent with congestive heart failure. Approximately, one-third of these patients will completely recover, one-third will have chronic congestive heart failure, and one-third may have a progressive cardiomyopathy that may require cardiac transplantation in severe cases.
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Postpartum fluid shifts occur during involution of the uterus and the ...