A nurse is assessing a pregnant patient in the third trimester who reports dizziness when lying flat. What is the most likely cause?
Increased cardiac output
Supine hypotensive syndrome
Physiological anemia
Hyperventilation
The Correct Answer is B
Supine hypotensive syndrome occurs in late pregnancy when the gravid uterus compresses the inferior vena cava while lying supine, reducing venous return and 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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is ["A","B","C"]
Explanation
Renal changes in pregnancyoccur due to hormonal and mechanical effects. Glomerular filtration rate (GFR)increases by 40–50% from early pregnancy, lowering serum creatinine (0.4–0.7 mg/dL) and blood urea nitrogen (BUN) (7–12 mg/dL vs non-pregnant 10–20 mg/dL). Urinary frequencyresults from increased GFR and bladder compression by the uterus. Progesteronecauses smooth muscle relaxation, leading to dilation of the renal pelvesand ureters, increasing stasis and risk for urinary tract infections. Mild glycosuriamay appear due to lower renal glucose threshold but does not always indicate gestational diabetes.
Rationale for correct answers
1.GFR increases 40–50% beginning early in pregnancy due to renal vasodilation and higher plasma volume. This is a physiologic adaptation.
2.Urinary frequency is common because of increased GFR and mechanical compression of the bladder by the enlarging uterus.
3.Dilation of renal pelves and ureters, known as hydronephrosis of pregnancy, occurs from progesterone-induced smooth muscle relaxation and uterine pressure. This increases UTI risk.
Rationale for incorrect answers
4.Serum creatinine and BUN do not increase. Instead, both decrease due to higher GFR. Normal serum creatinine in pregnancy is 0.4–0.7 mg/dL compared to 0.6–1.1 mg/dL in non-pregnant women. BUN decreases to 7–12 mg/dL.
5.Glycosuria does not always indicate gestational diabetes. It is often physiologic due to decreased renal threshold for glucose excretion. Only persistent or high-level glycosuria warrants further evaluation with glucose tolerance testing.
Take home points
• GFR increases 40–50% in pregnancy, lowering creatinine and BUN levels.
• Urinary frequency is due to both increased filtration and uterine compression.
• Ureteral and pelvic dilation increase the risk for urinary tract infections.
• Mild glycosuria is physiologic, but persistent glycosuria needs evaluation for gestational diabetes.
Correct Answer is B
Explanation
Estrogenis a steroid hormonethat rises significantly in pregnancy, produced mainly by the placentaafter the first trimester. It influences neurotransmitter regulation, particularly serotonin and dopamine, which are involved in mood control. Rapidly increasing estrogen levels contribute to mood swings, irritability, and emotional lability often reported during pregnancy. Normal estradiol levels increase from ~50–350 pg/mL (follicular phase) to >10,000–40,000 pg/mL in late pregnancy.
Rationale for correct answer
2.Estrogen fluctuations and high levels alter central nervous system neurotransmission, especially serotonin, leading to emotional instability and mood swings. This is the primary hormonal factor for psychological changes during pregnancy.
Rationale for incorrect answers
1.Human placental lactogen regulates maternal glucose metabolism and increases insulin resistance to ensure fetal glucose supply. It does not act directly on neurotransmitters or cause mood swings.
3.Insulin regulates blood glucose by facilitating cellular glucose uptake. While hypoglycemia or hyperglycemia can cause irritability, insulin itself is not the hormonal cause of mood swings in pregnancy.
4.Thyroxine (T4) regulates metabolism and oxygen consumption. Abnormal thyroid hormone levels can cause anxiety or depression, but normal pregnancy mood swings are not primarily due to thyroxine.
Take home points
• Estrogen is the main hormone responsible for mood swings in pregnancy.
• High estrogen levels affect serotonin and dopamine pathways in the brain.
• Human placental lactogen and insulin regulate glucose, not emotions.
• Thyroxine regulates metabolism; abnormal levels may mimic mood changes but are not typical causes.
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