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Dyspnea during pregnancy

Steven E Weinberger, MD
Section Editors
Charles J Lockwood, MD, MHCM
Peter J Barnes, DM, DSc, FRCP, FRS
Deputy Editor
Kristen Eckler, MD, FACOG


Dyspnea is common during pregnancy. The development of dyspnea in the pregnant woman raises the question as to whether she has some form of either underlying or new cardiac or pulmonary disease, or whether her dyspnea is due to the pregnancy itself. Making this assessment requires an understanding of the cardiopulmonary changes that occur during normal pregnancy, as well as recognition of the syndrome of dyspnea during normal pregnancy [1-4].


Cardiovascular changes — The most striking cardiovascular changes during pregnancy are increases in blood volume and cardiac output [5-7].

Blood volume — Blood volume starts to rise during the first trimester and eventually reaches a maximum that is 40 to 50 percent above the baseline, nonpregnant blood volume. Because plasma volume increases more than red cell mass, the hematocrit generally falls, resulting in the physiologic "anemia of pregnancy" (figure 1). (See "Hematologic changes in pregnancy".)

Cardiac output — Cardiac output also starts to rise in the first trimester, reaching a peak at 20 to 32 weeks of gestation that is 30 to 50 percent above baseline (figure 2) [7,8]. Although the increase in cardiac output is initially due to a rise in stroke volume, the increase is maintained later in pregnancy by an increase in heart rate, as stroke volume falls during the third trimester. A decrease in systemic vascular resistance accompanies the increase in cardiac output. Blood pressure during pregnancy is often notable for a rise in pulse pressure due to an unchanged systolic pressure accompanied by a decrease in diastolic pressure. (See "Maternal cardiovascular and hemodynamic adaptations to pregnancy".)

Respiratory changes — The normal respiratory tract changes during pregnancy result in a compensated respiratory alkalosis, with a higher PO2 and a lower PCO2 than in the nonpregnant state. The lower PCO2 is thought to provide a diffusion gradient that may facilitate the fetus' ability to eliminate waste from aerobic metabolism.


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Literature review current through: May 2017. | This topic last updated: Mar 17, 2017.
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