A 26-year-old woman, gravida 1, para 0, presents for a scheduled prenatal visit at 27 week… — USMLE Step 2 CK

A 26-year-old woman, gravida 1, para 0, presents for a scheduled prenatal visit at 27 weeks gestation. Her last prenatal visit was at 22 weeks. The patient reports urinating more frequently and experiencing a mild, dull ache in her right flank for the past week. She denies dysuria, hematuria, fever, and chills. Vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure $110/68 \text{ mm Hg}$ , and pulse $86/\text{min}$ . Physical examination shows a gravid uterus consistent with dates and trace bilateral lower extremity edema. There is mild right costovertebral angle tenderness. Fetal heart tones are $145/\text{min}$ .

Laboratory results are as follows:
Hemoglobin: $10.8 \text{ g/dL}$
Leukocyte count: $14,500/\text{mm}^3$
Platelets: $175,000/\text{mm}^3$
Serum creatinine: $0.5 \text{ mg/dL}$

Urinalysis:
Protein: Trace
Glucose: $1+$
Leukocyte esterase: Negative
Nitrites: Negative
WBC: $2-3/\text{hpf}$
RBC: $0-1/\text{hpf}$

A transabdominal renal ultrasound demonstrates mild dilation of the right renal pelvis and proximal ureter. The left kidney is normal.

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

Administer a 1-hour 50-g oral glucose challenge testAnswer
B
Proceed directly to a 3-hour 100-g oral glucose tolerance test
C
Prescribe oral cephalexin and order a urine culture
D
Obtain a 24-hour urine collection for total protein
E
Refer for cystoscopy and double-J ureteral stent placement

Answer

The most appropriate next step is to administer a 1-hour 50-g oral glucose challenge test as part of routine prenatal screening.

The correct action is to proceed with the routine 1-hour 50-g oral glucose challenge test. The patient is at 27 weeks gestation, making this the appropriate time for universal gestational diabetes screening (indicated between 24-28 weeks). All clinical and laboratory findings presented in the vignette represent normal physiologic changes of pregnancy, requiring no further diagnostic workup or intervention. The increased glomerular filtration rate (GFR) normally seen in pregnancy causes a decreased serum creatinine, trace proteinuria, and glucosuria (as the filtered glucose load exceeds the tubular reabsorption capacity). Dilutional anemia (hemoglobin > 10.5 g/dL in the second trimester is normal) and physiologic leukocytosis are also expected. Furthermore, dextrorotation of the gravid uterus commonly compresses the right ureter at the pelvic brim, causing asymptomatic or mildly symptomatic right-sided hydronephrosis that requires only observation.

Step-by-Step Solution

Analyze the patient's symptoms and imaging findings (urinary frequency, right flank ache, right hydronephrosis on ultrasound).

These are recognized as normal physiologic changes of pregnancy, specifically caused by the dextrorotated gravid uterus compressing the right ureter and bladder.

Differentiating physiologic adaptations from true pathology is critical to avoid unnecessary interventions.

Evaluate the laboratory results (hemoglobin 10.8 g/dL, WBC 14,500/mm³, creatinine 0.5 mg/dL, trace proteinuria, 1+ glucosuria).

All laboratory values are within normal limits for the late second/early third trimester. Increased GFR explains the low creatinine, trace protein, and glucosuria. Plasma volume expansion explains the dilutional anemia, and leukocytosis is a physiologic stress response.

Misinterpreting these values could incorrectly lead to a diagnosis of gestational diabetes, preeclampsia, or pyelonephritis.

Determine the routine prenatal care requirements based on the patient's gestational age (27 weeks) and prenatal care timeline.

The patient is due for her standard 24-28 week screening, which includes a 1-hour 50-g oral glucose challenge test.

Since all abnormal-appearing findings are actually physiologic, standard preventative prenatal care is the only indicated next step.

Key Concept

Normal physiologic changes of pregnancy heavily alter standard laboratory values (e.g., leukocytosis, dilutional anemia, glucosuria, trace proteinuria) and imaging findings (e.g., right-sided hydronephrosis). Recognition of these changes prevents unnecessary diagnostic workups, allowing the clinician to proceed with routine indicated prenatal screening.

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