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Difficulty: MediumNormal Pregnancy and Prenatal Care

Presenting with a dull, continuous ache in her right flank, a primigravid patient at 2626 weeks gestation is evaluated in the obstetric triage unit. She first noticed the discomfort yesterday. There is no radiation of the pain to the groin, and she has not experienced any fever, chills, urinary frequency, or dysuria. Her temperature is 37.1∘C37.1^\circ\text{C} (98.8∘F98.8^\circ\text{F}), blood pressure is 110/68110/68 mm Hg, and pulse is 8282/min. Physical examination shows a gravid uterus consistent with gestational age and trace tenderness over the right costovertebral angle. Laboratory results are as follows:

Hemoglobin: 11.211.2 g/dL
Leukocyte count: 10,500/mm310,500/\text{mm}^3
Blood urea nitrogen: 77 mg/dL
Serum creatinine: 0.50.5 mg/dL

Urinalysis is negative for blood, nitrites, and leukocyte esterase, showing 11-22 WBCs/hpf. A right upper quadrant and renal ultrasound reveals mild dilation of the right renal pelvis and proximal ureter, without visible echogenic foci or acoustic shadowing. The left kidney appears normal. Which of the following is the most appropriate next step in management?

  1. Observation and routine obstetric careAnswer
  2. B
    Prescribe empiric oral cephalexin therapy
  3. C
    Order a non-contrast computed tomography scan of the abdomen
  4. D
    Admit the patient for intravenous antibiotics and hydration
  5. E
    Refer to urology for cystoscopy and ureteral stent placement

Answer

Observation and routine obstetric care
The correct management is observation and routine obstetric care because the patient's presentation represents normal physiologic hydroureteronephrosis of pregnancy. During pregnancy, increased progesterone levels cause smooth muscle relaxation, leading to mild ureteral dilation. Additionally, as the gravid uterus enlarges, it naturally dextrorotates (tilts to the right). This mechanical shift compresses the right ureter as it crosses the iliac vessels at the pelvic brim, making right-sided hydronephrosis much more prominent and common than left-sided dilation.

The patient's laboratory values are perfectly aligned with normal physiologic adaptations to pregnancy: her blood urea nitrogen and creatinine are mildly decreased due to a pregnancy-induced increase in glomerular filtration rate (GFR), and her mild dilutional anemia and leukocytosis are normal. Because the urinalysis is negative and there are no signs of infection or obstructive stones on the ultrasound, no intervention is required.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient has a right-sided flank ache with trace CVA tenderness, but lacks infectious symptoms such as fever, dysuria, or urinary frequency.
Differentiating physiologic musculoskeletal or renal distension pain from infectious or obstructive pathology is critical in pregnancy.
2
Interpret laboratory data within the context of gestational age.
The mild anemia (11.211.2 g/dL), mild leukocytosis (10,500/mm310,500/\text{mm}^3), and decreased BUN (77 mg/dL) and creatinine (0.50.5 mg/dL) are entirely normal physiologic changes of pregnancy.
Pregnancy causes plasma volume expansion, physiological stress, and a 50%50\% increase in the glomerular filtration rate (GFR).
3
Evaluate the ultrasound findings and urinalysis.
The negative urinalysis rules out infection. The ultrasound shows isolated mild right-sided hydronephrosis without stones.
Right-sided hydronephrosis is a common normal finding due to mechanical compression of the ureter by the dextrorotated uterus.
4
Determine the most appropriate management.
Observation and routine obstetric care.
Since the findings are physiologic and asymptomatic (or mildly symptomatic without true pathology), expectant management is indicated.

Key Concept

Physiologic maternal adaptations: Hydroureteronephrosis of pregnancy
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Topics

Normal Pregnancy and Prenatal Care

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