A stable newborn male has a prenatal history of unilateral hydronephrosis. To ensure accurate assessment and minimize false negatives due to transient physiological oliguria, when should the postnatal renal ultrasound be obtained?

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TheoryPractice · Accepted Answer

After 48 hours of life. The correct answer is after 48 hours of life (often 48-72 hours or later). Newborns experience physiological dehydration and transient oliguria in the first 2 days, which can underestimate the degree of hydronephrosis. Imaging too early may yield a false-negative result. Distractor 1 is incorrect because immediate imaging is prone to this dehydration artifact. Distractor 2 is incorrect as waiting 4 weeks is too long for an initial postnatal evaluation of significant antenatal findings. Distractor 3 and 4 are incorrect because the timing is dictated by physiology, not discharge convenience or symptoms.

A stable newborn male has a prenatal history of unilateral hydronephrosis. To ensure accurate assessment and minimize false negatives due to transient physiological oliguria, when should the postnatal renal ultrasound be obtained?

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