Decreased heart rate.
Increased cardiac output in the supine position during the third trimester.
Increased systolic and diastolic blood pressures during the second trimester.
Increased supraventricular ectopy.
Decreased plasma volume.
Physiologic changes occur in pregnancy that may be confused with abnormal medical conditions or, in the case of trauma, hypovolemia, and internal hemorrhage. The heart rate normally increases during pregnancy, reaching 15–20 beats above the nonpregnant rate in the late third trimester. Blood pressure falls by 10–15 mm Hg by the second trimester; blood plasma volume increases by 33% (450 mL) and blood volume by 45%. A physiologic anemia is the result, and this increased plasma volume should be considered when managing fluids in the pregnant trauma patient. Because the uterus will compress the inferior vena cava in the supine position later in pregnancy, cardiac output will fall and may result in hypotension.