Which respiratory change is normal in pregnancy?
Decreased tidal volume
Increased minute ventilation
Reduced oxygen consumption
Increased functional residual capacity
The Correct Answer is B
Respiratory adaptations in pregnancy include increased minute ventilation, driven mainly by elevated tidal volume due to progesterone stimulation of the respiratory center. Normal tidal volume increases by about 30–40% (from 500 mL to ~650–700 mL), while minute ventilation increases by 30–50%. Oxygen consumption rises by 20–30% to meet maternal–fetal demands. Functional residual capacity decreases by ~20% due to upward displacement of the diaphragm by the gravid uterus.
Rationale for correct answer
2. Increased minute ventilation occurs because tidal volume rises while respiratory rate remains relatively stable. Progesterone increases sensitivity to CO₂, lowering PaCO₂ to 28–32 mmHg and causing mild respiratory alkalosis, a normal physiological adaptation.
Rationale for incorrect answers
1. Tidal volume does not decrease in pregnancy; it increases by 30–40% due to progesterone. A decrease would impair oxygen delivery, which is incompatible with normal pregnancy physiology.
3. Oxygen consumption increases by 20–30% to support maternal metabolism and fetal growth. A reduction would compromise oxygen delivery to both mother and fetus.
4. Functional residual capacity decreases by about 20% because the diaphragm is elevated up to 4 cm by the gravid uterus. An increase is not possible due to reduced thoracic space.
Take home points
• Minute ventilation increases in pregnancy due to higher tidal volume.
• Progesterone drives hyperventilation, lowering maternal PaCO₂ to 28–32 mmHg.
• Oxygen consumption increases 20–30% to meet maternal and fetal needs.
• Functional residual capacity decreases due to diaphragmatic elevation by the enlarged uterus.
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Related Questions
Correct Answer is D
Explanation
Hypercoagulability in pregnancydevelops as a protective adaptation to minimize hemorrhageat delivery, but it also increases the risk of thromboembolism. There is a marked rise in fibrinogenand several clotting factors(VII, VIII, IX, X, XII), while fibrinolytic activity decreases. Normal fibrinogen levels in nonpregnant women are 200–400 mg/dL, but in pregnancy, they rise to 400–650 mg/dL. This procoagulant state peaks in the third trimester and the puerperium.
Rationale for correct answer
2.Increased fibrinogen levels contribute to the hypercoagulable state of pregnancy. Elevated fibrinogen enhances clot formation and is a major factor in increasing the risk of venous thromboembolism, which is one of the leading causes of maternal morbidity and mortality.
Rationale for incorrect answers
1.Decreased clotting factors would reduce coagulation and increase the risk of bleeding, not thrombosis. Pregnancy is characterized by increased clotting factor activity, not reduction.
3.Reduced platelet count (gestational thrombocytopenia) can occur, but it is usually mild and not enough to outweigh the hypercoagulable changes. A lower platelet count actually tends toward bleeding risk, not thromboembolism.
4.Decreased white blood cell count is not typical in pregnancy. Instead, leukocytosis (WBC up to 12,000–15,000/µL, sometimes 25,000/µL in labor) is common. White blood cell levels are not directly related to thromboembolic risk in pregnancy.
Take home points
• Pregnancy is a hypercoagulable state due to increased fibrinogen and clotting factors.
• Elevated fibrinogen levels (400–650 mg/dL) significantly increase thromboembolism risk.
• Platelet count may slightly fall, but this does not negate the hypercoagulable effect.
• Thromboembolism is a major cause of maternal morbidity and mortality, especially postpartum.
Correct Answer is ["A","C","D"]
Explanation
Respiratory changes in pregnancyare driven by hormonal and mechanical factors to meet higher oxygen demand. Progesteroneincreases respiratory center sensitivity to CO₂, raising tidal volumeby about 30–40%. Minute ventilationrises by 30–50%, leading to mild respiratory alkalosis with PaCO₂ 28–32 mmHg (normal non-pregnant PaCO₂ 35–45 mmHg). Oxygen consumptionincreases by 15–20% due to fetal and maternal metabolic needs. The enlarging uterus elevates the diaphragm, reducing functional residual capacityby 20%. Respiratory rateremains unchanged or slightly increased, not decreased.
Rationale for correct answers
1.Tidal volume increases by 30–40% from progesterone stimulation of the respiratory center. This enhances alveolar ventilation and maintains maternal-fetal gas exchange.
3.Oxygen consumption increases 15–20% to meet maternal and fetal metabolic demands. This adaptation ensures sufficient oxygen delivery across the placenta.
4.Functional residual capacity decreases by about 20% due to diaphragm elevation from the gravid uterus. This lowers lung reserve volume and contributes to dyspnea in late pregnancy.
Rationale for incorrect answers
2.Minute ventilation does not decrease. Instead, it increases by 30–50% because of higher tidal volume. A decrease would cause hypercapnia and impair placental gas exchange.
5.Respiratory rate does not decrease. It usually remains stable or slightly increases by 1–2 breaths/min. A decrease would reduce alveolar ventilation and worsen hypoxemia risk.
Take home points
• Pregnancy increases tidal volume and minute ventilation, not respiratory rate.
• Oxygen consumption rises by 15–20% to support maternal-fetal metabolism.
• Functional residual capacity decreases due to diaphragm elevation.
• Maternal PaCO₂ is reduced to 28–32 mmHg, causing mild compensated respiratory alkalosis.
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