A 32-year-old female, currently in her second pregnancy (G2P1) at 34 weeks of gestation, i… — USMLE Step 2 CK

A $32$ -year-old female, currently in her second pregnancy (G2P1) at $34$ weeks of gestation, is evaluated in the emergency department for shortness of breath and leg swelling. She states that the breathlessness has gradually developed over the past few weeks and is most noticeable when she lies flat in bed. She denies chest pain, cough, or pain in her legs. Her medical history is unremarkable, and her pregnancy has been uncomplicated.

Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure of $112/70\text{ mmHg}$ , pulse of $86\text{/min}$ , and respirations of $16\text{/min}$ . Oxygen saturation is $99\%$ on ambient air.

Physical examination demonstrates 1+ symmetric, bilateral pitting edema extending to the ankles. The maximum circumference of the right calf is $35.0\text{ cm}$ and the left calf is $35.5\text{ cm}$ . Cardiac auscultation reveals a grade 2/6 early systolic murmur at the left sternal border. The lungs are clear to auscultation bilaterally.

Laboratory analysis reveals the following:

Hemoglobin: $10.6\text{ g/dL}$
Platelet count: $145,000\text{/mm}^3$
D-dimer: $920\text{ ng/mL}$ (Reference: $< 500\text{ ng/mL}$ )

Arterial blood gas analysis on ambient air:
pH: $7.44$
PaO $_2$ : $104\text{ mmHg}$
PaCO $_2$ : $29\text{ mmHg}$
HCO $_3^-$ : $19\text{ mEq/L}$

Which of the following is the most appropriate next step in the management of this patient?

Reassurance and routine obstetric follow-upAnswer
B
Compression duplex ultrasonography of the lower extremities
C
Computed tomography pulmonary angiography
D
Transthoracic echocardiography
E
24-hour urine collection for total protein

Answer

Reassurance and routine obstetric follow-up

The correct answer is reassurance and routine obstetric follow-up because this patient's clinical and laboratory findings entirely represent normal physiologic adaptations to pregnancy. Progesterone directly stimulates the medullary respiratory center, increasing minute ventilation (primarily via increased tidal volume) and resulting in a chronic, compensated respiratory alkalosis (pH slightly alkalotic, low PaCO

_2

, and a compensatory decrease in HCO

_3^-

). The growing uterus elevates the diaphragm, which can cause a subjective feeling of breathlessness, particularly when supine. Additionally, normal pregnancy is a hypercoagulable state with physiologically increased D-dimer levels; therefore, a D-dimer test has virtually no negative predictive value in the third trimester. Her symmetric edema and grade 2/6 systolic ejection murmur are expected consequences of increased plasma volume and cardiac output. Since she lacks acute or focal signs of pathology (such as tachycardia, hypoxia, asymmetric leg swelling, or hypertension), reassurance is the most appropriate management.

Step-by-Step Solution

Analyze the patient's presenting symptoms and vital signs.

The patient reports a gradual onset of dyspnea and orthopnea, with symmetric leg swelling. Vital signs are strictly within normal limits, including normal oxygen saturation and heart rate.

Establishing the acuity of the presentation helps differentiate between life-threatening emergencies (e.g., pulmonary embolism) and physiologic changes of the third trimester.

Evaluate the physical examination findings.

Symmetric bilateral pitting edema and a 2/6 early systolic flow murmur are present. Lungs are clear, and there is no asymmetric calf swelling.

These findings are classic normal physiological adaptations driven by venous compression from the gravid uterus and increased maternal blood volume/cardiac output.

Interpret the laboratory and arterial blood gas (ABG) results in the context of pregnancy.

The patient has a primary respiratory alkalosis with metabolic compensation (pH

7.44

, low PaCO

_2

, low HCO

_3^-

). The D-dimer is elevated, and mild dilutional anemia is present.

Progesterone directly stimulates the medullary respiratory center, increasing minute ventilation and causing a chronic respiratory alkalosis. D-dimer naturally rises during normal pregnancy, rendering it useless for ruling out venous thromboembolism.

Synthesize the findings to determine the correct management.

Because all findings reflect normal pregnancy physiology and the patient has a Wells score of zero, no further diagnostic testing or treatment is indicated.

Empiric treatment or advanced imaging based on physiologically expected abnormal laboratory values leads to unnecessary healthcare interventions and patient anxiety.

Key Concept

Normal physiologic adaptations in the third trimester include dyspnea, symmetric lower extremity edema, systolic flow murmurs, physiologically elevated D-dimer levels, and a compensated primary respiratory alkalosis.

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