Prenatal Diagnosis and Fetal Urology
Core concepts
Understand the antenatal evaluation of hydronephrosis: timing, severity, and the use of the UTD classification. Recognize the causes of antenatal hydronephrosis: UPJ obstruction, UVJ obstruction, vesicoureteral reflux, posterior urethral valves, and duplicated systems. Know the role of fetal MRI and the indications for prenatal intervention. Understand the significance of oligohydramnios and its association with renal agenesis or severe obstruction. Recognize the difference between unilateral and bilateral hydronephrosis and the implications for postnatal evaluation. Know the timing of postnatal imaging: ultrasound after the first week, VCUG when indicated, and the role of renal scintigraphy.
Traps
- Assuming all antenatal hydronephrosis is obstructive; many cases are reflux or transient.
- Missing bilateral hydronephrosis with a thick-walled bladder as possible posterior urethral valves.
- Ordering postnatal imaging too early, when dehydration can underestimate dilation.
- Overlooking oligohydramnios as a marker of poor renal function.
Worked example
A fetus with bilateral hydronephrosis and a keyhole bladder suggests posterior urethral valves; postnatal evaluation includes ultrasound and VCUG, with catheter drainage if needed.
Rule of thumb
Antenatal hydronephrosis is a sign, not a diagnosis; postnatal imaging and sometimes VCUG determine the cause.