A healthy 25-year-old woman, who is pregnant for the first time, visits her obstetrician f… — USMLE Step 2 CK

A healthy $25$ -year-old woman, who is pregnant for the first time, visits her obstetrician for a scheduled mid-pregnancy evaluation at $26$ weeks of gestation. Her pregnancy has progressed normally without any complications, and her blood group is O positive. She states that she is feeling the baby move frequently. Her only new symptom is mild swelling in both ankles that appears in the late afternoon and resolves after resting overnight.

On physical assessment, her temperature is $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure is $112/68 \text{ mm Hg}$ , pulse is $85/\text{min}$ , and respiratory rate is $14/\text{min}$ . Cardiovascular auscultation reveals a soft, grade 1/6 systolic ejection murmur at the left upper sternal border. The abdomen is non-tender, and the distance from the pubic symphysis to the top of the uterus measures $26 \text{ cm}$ . Trace pitting edema is noted symmetrically on the lower legs.

A panel of screening tests is performed with the following results:

Hemoglobin: $10.9 \text{ g/dL}$
Mean corpuscular volume: $89 \text{ fL}$
Leukocyte count: $11,800/\text{mm}^3$
Platelet count: $195,000/\text{mm}^3$
1-hour 50-g oral glucose challenge test: $132 \text{ mg/dL}$

Based on these findings, which of the following is the most appropriate action?

Proceed with standard scheduled prenatal careAnswer
B
Prescribe daily therapeutic oral iron
C
Schedule a 3-hour 100-g glucose tolerance test
D
Perform a resting 12-lead electrocardiogram
E
Obtain bilateral lower extremity venous ultrasonography

Answer

The correct approach is to proceed with standard scheduled prenatal care, as all findings represent normal physiological adaptations and normal screening test results for a pregnancy at

26

weeks.

The correct approach is to proceed with standard scheduled prenatal care. This patient is experiencing expected physiological adaptations to pregnancy. Her grade 1/6 systolic murmur is a benign flow murmur resulting from increased cardiac output. Her trace bilateral ankle swelling is a classic mechanical consequence of the enlarging uterus compressing the inferior vena cava, which increases venous pressure in the lower extremities. Her hemoglobin of

10.9 \text{ g/dL}

is entirely normal for the second trimester (the cutoff for anemia in the second trimester is

< 10.5 \text{ g/dL}

). Her mild leukocytosis is also a normal finding in pregnancy. Finally, her 1-hour glucose challenge test result is

< 140 \text{ mg/dL}

, ruling out gestational diabetes. Therefore, no additional interventions are required.

Step-by-Step Solution

Evaluate the patient's cardiovascular findings.

The grade 1/6 systolic ejection murmur and trace, symmetric, gravity-dependent pedal edema are identified.

Pregnancy induces a 30-50% increase in blood volume and cardiac output, leading to benign flow murmurs. The gravid uterus compresses the inferior vena cava, leading to benign dependent edema. No pathologic signs (e.g., diastolic murmur, unilateral swelling) are present.

Interpret the hematologic laboratory values.

Hemoglobin is

10.9 \text{ g/dL}

and leukocyte count is

11,800/\text{mm}^3

Plasma volume increases more than red blood cell mass in pregnancy, causing a dilutional anemia. The second-trimester threshold for true anemia is hemoglobin

< 10.5 \text{ g/dL}

. Furthermore, a mild leukocytosis (up to

15,000/\text{mm}^3

) is a normal physiological stress response during pregnancy.

Analyze the metabolic screening result.

The 1-hour 50-g glucose challenge test result is

132 \text{ mg/dL}

The standard threshold for a positive 1-hour screen requiring a confirmatory 3-hour test is

\geq 140 \text{ mg/dL}

(or

\geq 135 \text{ mg/dL}

in some institutions). A value of

132 \text{ mg/dL}

is definitively normal.

Determine the necessary medical action.

No additional diagnostic tests or therapies are indicated.

Because all clinical and laboratory parameters reflect normal physiological changes or normal screening values, the appropriate management is routine prenatal care.

Key Concept

Pregnancy induces significant multiorgan physiological changes, including a dilutional decrease in hemoglobin, increased cardiac output leading to benign flow murmurs, and mechanical compression causing dependent edema. Recognizing these adaptations is crucial to avoid unnecessary interventions.

Estimated Time:1m 15s

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