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Maternal adaptations to pregnancy: Physiologic respiratory changes and dyspnea

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, or breathing discomfort, is common during pregnancy. Dyspnea during pregnancy can represent either underlying or new cardiac or pulmonary disease, or, more commonly, be a result of the pregnancy itself.


Distinguishing physiologic dyspnea of pregnancy from other causes requires an understanding of both the cardiopulmonary changes that occur during normal pregnancy and the syndrome of dyspnea during normal pregnancy [1-4]. Both cardiovascular and respiratory changes accompany normal pregnancy.

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 "Maternal adaptations to pregnancy: Hematologic changes".)

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. Decreases in systemic vascular resistance and pulmonary vascular resistance accompany the increase in cardiac output [9]. 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 adaptations to pregnancy: Cardiovascular and hemodynamic changes".)

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Literature review current through: Nov 2017. | This topic last updated: Aug 03, 2017.
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