Supine hypotensive syndrome is caused by:

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.

Physiological anemia in pregnancyis caused by an increased plasma volumerelative to red blood cell mass. Plasma volume expands by 40–50% while red blood cell mass rises only 20–30%, leading to hemodilution. The normal hemoglobin range in pregnancy is 11–13 g/dL, and hematocrit falls to 32–36%. This adaptation enhances uteroplacental perfusion but predisposes to symptoms like fatigueand paleness.

Rationale for correct answer

3.Plasma volume increases more than red blood cell mass, resulting in hemodilution and relative anemia. This explains the physiological anemia observed during pregnancy, which ensures optimal placental perfusion without true reduction in oxygen-carrying capacity.

Rationale for incorrect answers

1.Increased red blood cell mass does occur, but it is not sufficient to match the larger plasma volume expansion. Therefore, while it increases oxygen delivery, it does not cause anemia.

2.Decreased plasma volume is opposite of what occurs in pregnancy. Plasma volume expands significantly under estrogen and aldosterone influence, ensuring greater blood flow to the placenta.

4.Cardiac output increases by 30–50% in pregnancy due to increased stroke volume and heart rate. This enhances systemic and placental circulation but does not directly explain anemia.

Take home points

• Physiological anemia in pregnancy results from disproportionate plasma volume expansion.

• Hemoglobin values normally fall to 11–13 g/dL, hematocrit to 32–36% in pregnancy.

• Cardiac output and blood volume increase but oxygen-carrying capacity is maintained.

• Differentiate physiological anemia from iron-deficiency anemia, which lowers hemoglobin below 11 g/dL.