An expectant mother at 31 weeks of gestation arrives at the obstetric clinic for a routine… — USMLE Step 2 CK

An expectant mother at $31$ weeks of gestation arrives at the obstetric clinic for a routine assessment. The $27$ -year-old patient notes that over the past few weeks, her shoes have felt tight by the evening and she experiences mild dyspnea after walking up a single flight of stairs. She denies headaches, visual disturbances, and right upper quadrant abdominal pain. Vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure $116/74\text{ mm Hg}$ , pulse $96/\text{min}$ , and respirations $18/\text{min}$ . Physical examination reveals a point of maximal impulse that is displaced upward and to the left. Cardiac auscultation demonstrates an early systolic murmur (grade $2/6$ ) at the left sternal border and an audible third heart sound ( $S_3$ ). Lungs are clear to auscultation bilaterally. The lower extremities show $1+$ bilateral pitting edema. Laboratory evaluation reveals the following:

Leukocyte count: $13,500/\text{mm}^3$
Hemoglobin: $11.2\text{ g/dL}$
Platelet count: $155,000/\text{mm}^3$
Serum creatinine: $0.5\text{ mg/dL}$

Urine dipstick is negative for protein. Which of the following is the most appropriate action for this patient's current presentation?

A
Obtain a transthoracic echocardiogram to evaluate the cardiac murmur
B
Order a 24-hour urine collection for total protein quantification
Advise the patient that these findings are expected and maintain the current care planAnswer
D
Prescribe an oral iron supplement to address the laboratory findings
E
Perform a comprehensive infectious disease workup for the elevated leukocyte count

Answer

Advise the patient that these findings are expected and maintain the current care plan

The correct action is to reassure the patient and continue routine prenatal care, as her clinical presentation reflects classic physiological adaptations to pregnancy. In the third trimester, maternal blood volume increases by up to 50%, leading to an increased cardiac output that often manifests as a prominent point of maximal impulse, a benign early systolic ejection murmur, and an S3 gallop. The growing uterus displaces the diaphragm upward, causing mild dyspnea, and compresses the inferior vena cava, resulting in dependent pedal edema. Furthermore, her laboratory findings are completely normal: the hemoglobin level of 11.2 g/dL is above the third-trimester threshold for anemia (< 11.0 g/dL) due to normal hemodilution, and her leukocyte count of 13,500/mm^3 is a well-documented physiological leukocytosis of pregnancy.

Step-by-Step Solution

Analyze the patient's symptoms and physical exam findings in the context of late pregnancy.

The dyspnea, dependent edema, displaced point of maximal impulse, grade 2/6 systolic murmur, and S3 gallop are identified as standard physiological adaptations.

Increased plasma volume and cardiac output cause functional flow murmurs and an S3, while the expanding uterus displaces the diaphragm upward and compresses the inferior vena cava, causing mild dyspnea and pedal edema.

Evaluate the laboratory results against pregnancy-specific reference ranges.

Hemoglobin of 11.2 g/dL and a leukocyte count of 13,500/mm^3 are both within normal limits for a pregnant patient.

Dilutional anemia occurs because plasma volume expansion (40-50%) exceeds red blood cell mass expansion (20-30%). A physiologic leukocytosis is also expected during normal pregnancy.

Determine the most appropriate clinical intervention based on the assessment.

No additional diagnostic testing or medication is required.

All clinical and laboratory findings reflect a normal, healthy pregnancy progression, making routine prenatal care the only necessary action.

Key Concept

Normal physiologic adaptations of pregnancy include mild exertional dyspnea, dependent edema, a systolic flow murmur, an S3 gallop, dilutional anemia, and mild leukocytosis.

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