Which of the following endocrine glands or organs undergo significant functional changes during pregnancy? Select all that apply.

Supine hypotensive syndromeoccurs in late pregnancy when the gravid uteruscompresses the inferior vena cavawhile lying supine, reducing venous returnand decreasing cardiac output. This leads to maternal hypotension, dizziness, pallor, and tachycardia. Normal maternal cardiac output in pregnancy increases by 30–50% (from 4.5 L/min to 6–7 L/min).

Rationale for correct answer

2.Supine hypotensive syndrome results from compression of the inferior vena cava by the enlarged uterus, especially in the third trimester. This reduces venous return, lowers preload, and decreases cardiac output, causing dizziness when lying flat. Symptoms resolve when the woman turns to the left lateral position.

Rationale for incorrect answers

1.Increased cardiac output occurs in pregnancy due to increased blood volume and stroke volume, peaking at 30–50% above baseline. This increase improves tissue perfusion and does not cause dizziness when supine. Instead, reduced output from vena cava compression explains the symptom.

3.Physiological anemia in pregnancy results from plasma volume expansion exceeding red cell mass increase, leading to lower hematocrit values (normal pregnancy hemoglobin 11–12 g/dL, hematocrit 32–34%). It causes fatigue and pallor, not positional dizziness specific to lying supine.

4.Hyperventilation occurs due to progesterone-mediated respiratory drive increase, leading to mild respiratory alkalosis (PaCO₂ 28–32 mmHg, normal pregnancy pH 7.40–7.45). This causes dyspnea but not dizziness limited to supine position.

Take home points

• Supine hypotensive syndrome results from gravid uterine compression of the inferior vena cava.

• Symptoms include dizziness, pallor, hypotension, and tachycardia when lying flat.

• Turning to the left lateral position relieves symptoms by restoring venous return.

• Physiological anemia and hyperventilation are normal pregnancy changes but do not explain positional dizziness.

Uterine enlargement in pregnancyis primarily caused by hypertrophyof smooth muscle fibers accompanied by hyperplasiaunder the influence of estrogen and progesterone. Increased vascularizationsupports tissue growth and enlargement. The uterus grows from 70 g to about 1100 g by term. Uterine blood flow increases from 50 mL/min to 500–700 mL/min at term, with normal uterine artery resistance decreasing significantly.

Rationale for correct answer

2.Uterine growth occurs through hypertrophy, which is the increase in muscle cell size, and hyperplasia, which is the increase in the number of cells. Estrogen stimulates hyperplasia, while progesterone promotes hypertrophy. This dual mechanism explains the large size of the uterus at term.

Rationale for incorrect answers

1.Hyperplasia occurs in pregnancy, but atrophy does not. Atrophy is a reduction in cell size, which is opposite of what occurs in uterine enlargement. Muscle fibers increase in both number and size during pregnancy, making this option incorrect.

3.Uterine blood flow actually increases greatly in pregnancy. A decrease would compromise placental perfusion and fetal development. Normal blood flow rises from about 50 mL/min in nonpregnant state to 500–700 mL/min at term, therefore a decrease cannot explain uterine growth.

4.Development of new uterine cells from scratch does not occur. Instead, existing myometrial cells undergo hyperplasia and hypertrophy. Uterine cells are not newly created; the process is a modification of pre-existing smooth muscle fibers.

Take home points

• Uterine growth in pregnancy occurs through both hypertrophy and hyperplasia of smooth muscle.

• Estrogen primarily stimulates hyperplasia, while progesterone promotes hypertrophy.

• Uterine blood flow increases significantly to support placental perfusion and fetal growth.

• Atrophy and development of new cells from scratch are not physiological mechanisms in pregnancy.