Which of the following are normal cardiovascular changes in pregnancy? Select all that apply.
Increased blood volume
Decreased cardiac output
Increased heart rate
Increased systemic vascular resistance
Decreased hematocrit
Correct Answer : A,C,E
Cardiovascular changes in pregnancy are adaptive responses to support maternal and fetal needs. Blood volume increases by 40–50%, while heart rate rises by 10–20 beats/minute, resulting in increased cardiac output by 30–50%. Systemic vascular resistance decreases due to progesterone-mediated smooth muscle relaxation. Hematocrit decreases to 32–36% because plasma volume increases more than red blood cell mass, causing physiological anemia.
Rationale for correct answers
1. Blood volume increases by 40–50% in pregnancy to meet the metabolic demands of the fetus and placenta. This expansion enhances perfusion and prepares for blood loss at delivery.
3. Heart rate increases by 10–20 beats/minute, which contributes to elevated cardiac output. This change helps maintain adequate circulation to the uterus and other maternal organs.
5. Hematocrit decreases to 32–36% because plasma volume expands more than red blood cell mass. This hemodilution results in physiological anemia of pregnancy.
Rationale for incorrect answers
2. Cardiac output does not decrease; it increases by 30–50% due to elevated stroke volume and heart rate. This adaptation ensures optimal uteroplacental perfusion.
4. Systemic vascular resistance does not increase; it decreases under the vasodilatory influence of progesterone, prostaglandins, and nitric oxide. This maintains normal to slightly lower blood pressure despite expanded blood volume.
Take home points
• Pregnancy increases blood volume by 40–50% and cardiac output by 30–50%.
• Heart rate rises by 10–20 beats/minute to maintain uteroplacental circulation.
• Hematocrit decreases to 32–36% due to plasma volume expansion.
• Systemic vascular resistance decreases under progesterone influence, keeping blood pressure stable or slightly reduced.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
Respiratory changes in pregnancyare driven mainly by the hormonalinfluence of progesteroneon the respiratory center in the medulla. Progesterone increases sensitivity to carbon dioxide, lowering arterial PaCO₂ to 27–32 mmHg (normal 35–45 mmHg). This causes increased tidal volumeand minute ventilation, ensuring adequate maternal oxygen delivery and fetal gas exchange despite unchanged respiratory rate.
Rationale for correct answer
2.Progesterone stimulates the central respiratory center, increasing sensitivity to carbon dioxide. This leads to deeper breaths, thereby increasing tidal volume and maternal minute ventilation, which supports enhanced oxygen transfer to the fetus.
Rationale for incorrect answers
1.Oxygen demand does not decrease in pregnancy; instead, it increases by about 20–30% due to fetal and maternal metabolic requirements. Therefore, decreased oxygen demand is not a cause of increased tidal volume.
3.Functional residual capacity decreases by about 20% during pregnancy because the enlarged uterus elevates the diaphragm. A reduced FRC does not cause increased tidal volume; rather, it reflects decreased lung volumes.
4.Chest wall compliance is not reduced in pregnancy. Rib cage expansion actually increases chest wall dimensions to accommodate the growing uterus, and this adaptation does not explain the rise in tidal volume.
Take home points
• Progesterone stimulates the maternal respiratory center, causing hyperventilation in pregnancy.
• Arterial PaCO₂ decreases to 27–32 mmHg as a normal pregnancy adaptation.
• Tidal volume and minute ventilation increase, but respiratory rate remains largely unchanged.
• Oxygen demand increases by 20–30% during pregnancy to meet maternal and fetal needs.
Correct Answer is B
Explanation
Supine hypotensive syndromeoccurs when the gravid uterus causes compressionof the inferior vena cava, impairing venous return to the heart. This reduces preloadand cardiac output, leading to maternal hypotension, dizziness, pallor, and syncope. Normal systolic blood pressure in pregnancy is 100–120 mmHg, and diastolic is 60–80 mmHg. The condition appears after 20 weeks gestation when the uterus is large enough to obstruct venous return.
Rationale for correct answer
2.The gravid uterus compresses the inferior vena cava in the supine position, reducing venous return and cardiac output. This leads to hypotension and symptoms such as dizziness and pallor, defining supine hypotensive syndrome.
Rationale for incorrect answers
1.Compression of the aorta can occur in late pregnancy, but it does not primarily cause hypotension. Aortic compression mainly reduces uteroplacental perfusion and fetal oxygen delivery, not maternal blood pressure.
3.Peripheral vasodilation due to progesterone contributes to systemic vascular resistance reduction in pregnancy. However, it is a generalized adaptation of pregnancy, not the mechanism of acute hypotension in the supine position.
4.Cardiac output increases by 30–50% in pregnancy due to elevated stroke volume and heart rate. Supine position does not increase cardiac output but instead decreases it by restricting venous return.
Take home points
• Supine hypotensive syndrome results from inferior vena cava compression by the gravid uterus.
• It is most pronounced after 20 weeks gestation when the uterus is large.
• Symptoms include hypotension, dizziness, pallor, and syncope when lying supine.
• Management includes positioning the mother in the left lateral tilt to relieve vena cava compression.
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