A 29-year-old woman, gravida 1 para 0, at 18 weeks gestation comes to the emergency department due to severe right flank pain. The pain is sharp and paroxysmal and radiates to her labia. When the pain occurs, she has associated nausea and vomiting. The patient has no fever, hematuria, dysuria, or increased urinary frequency. She has no chronic medical conditions and has had no surgeries. Her pregnancy had been uncomplicated and initial prenatal laboratory testing was normal. The patient takes a daily prenatal vitamin and does not use tobacco, alcohol, or illicit drugs. Temperature is 36.7 C (98 F), blood pressure is 110/60 mm Hg, and pulse is 100/min. BMI is 32 kg/m². The abdomen is tender to palpation along the right side, but there is no rebound or guarding. Pelvic examination reveals an 18-week-sized uterus. Laboratory results are as follows: Which of the following is the most appropriate next step in management of this patient?

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Explanation: 11ec2b69_c09e_1a9a_8f63_b30ccd5ac5a2_MD0005_00 This patient's paroxysmal, severe flank pain that radiates to the labia is likely due to nephrolithiasis. Other clinical features of nephrolithiasis include nausea, vomiting, dysuria, hematuria, and pyuria. During pregnancy, nephrolithiasis is most common in the second and third trimesters. An increase in urinary calcium excretion, urinary stasis, and decreased bladder capacity predispose pregnant patients to the development of nephrolithiasis. Additional risk factors include obesity, hyperparathyroidism, diabetes mellitus, irritable bowel syndrome, and a history of nephrolithiasis outside of pregnancy. To avoid fetal radiation exposure, diagnosis of nephrolithiasis during pregnancy is via renal and pelvic ultrasound (US) (Choice B). Ultrasonography usually does not visualize a stone; however, US findings of hydronephrosis and hydroureter are consistent with ureteral obstruction due to nephrolithiasis. Most stones pass spontaneously; therefore, management of nephrolithiasis in pregnancy is generally supportive with pain control as needed. Nephrolithiasis that is complicated by persistent obstruction, intractable pain, or urinary tract infection may require surgical management. (Choice A) MRI urography is a second-line imaging modality for the diagnosis of nephrolithiasis during pregnancy and is indicated if US is nondiagnostic. (Choice C) A noncontrast helical CT scan is the most sensitive test for diagnosing nephrolithiasis and is the first-line modality in nonpregnant patients. However, CT scans are associated with fetal radiation exposure and are relatively contraindicated during pregnancy. CT scan may be considered during the second and third trimesters if US and/or MRI is not diagnostic or available. (Choice D) A quantitative β-hCG is indicated in the evaluation of an early pregnancy of unknown location. At this patient's gestational age, a β-hCG level provides no information; the pregnancy is better evaluated via US. Educational objective: Nephrolithiasis during pregnancy is most commonly seen during the second and third trimesters and can present with flank pain that radiates to the labia. During pregnancy, first-line imaging is with a renal and pelvic ultrasound as it minimizes fetal radiation exposure. References: Radiology of renal stone disease. (http://www.ncbi.nlm.nih.gov/pubmed/27816704)

A 29-Year-Old Woman, Gravida 1 Para 0, at 18 Weeks