Antenatal urinary tract dilation

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  • See also

    Urinary tract infection
    Recognition of the seriously unwell neonate and young infant

    Key points

    1. Dilation of the fetal renal collecting system is often benign, but may be caused by serious underlying pathology
    2. The goal of assessment is to identify babies with significant renal or urinary tract abnormalities, while limiting unnecessary radiographic studies
    3. A child with moderate to severe dilation (anterior posterior renal pelvic diameter >10 mm) requires further investigation and early referral to avert long-term complications


    • Antenatal urinary tract dilation (UTD) is a common abnormality detected on prenatal ultrasound, reported in up to 5% of pregnancies
    • The term UTD encompasses any dilation of the kidney, renal pelvis, ureter and/or bladder, replacing ambiguous terms such as hydronephrosis and pyelectasis
    • UTD encompasses a wide spectrum of conditions, ranging from transient and benign dilation of the renal pelvis to significant congenital anomalies of the kidney and urinary tract
    • The severity of UTD is determined by anterior-posterior renal pelvic diameter (APD or APRD) and/or degree of calyceal dilation via ultrasound
    • Urinary tract obstruction and vesicoureteric reflux (VUR) are important causes that may result in severe and chronic renal impairment. Early diagnosis and management may dramatically improve long-term outcomes


    The finding of UTD on antenatal ultrasound should prompt the clinician to look for the following on history and examination

    Antenatal findings

    • Degree of UTD (refer to table below)
    • Presence of calyceal dilation, ureteric dilation, cortical thinning, reduced corticomedullary differentiation or abnormal bladder
    • Unexplained oligohydramnios (do not attribute oligohydramnios to premature rupture of membranes where there is significant, and especially bilateral, urinary tract dilation)
    • Single kidney or other renal tract abnormalities

    Postnatal findings

    • Poor urinary stream (note: a normal urinary stream does not exclude bladder outlet obstruction)
    • Has not passed urine within first 24 hours of life
    • Palpable bladder
    • Palpable kidney
    • Urinary tract infection (Children with UTI in the absence of urinary tract dilation on antenatal ultrasound, see Urinary tract infection)

    Assessment of severity

    Degree of UTD

    Anterior Posterior Diameter (APD) of the renal pelvis
    measured at the maximum diameter of the intrarenal pelvis

    Second Trimester

    Third Trimester



    <5 mm

    <7 mm

    <5 mm


    5.1 – 7 mm

    7.1 – 10 mm

    5.1 – 10 mm


    7.1 – 10 mm

    10.1 – 15 mm

    10.1 – 15 mm


    >10 mm

    >15 mm

    >15 mm

    Note: Antenatal or early postnatal calyceal dilation or other abnormal findings, with or without UTD, would increase the level of concern


    Management of an infant with UTD diagnosed antenatally

    Management of an infant with UTD diagnosed antenatally 

    Management at 4 weeks of infant with UTD diagnosed antenatally

    Management at 4 weeks of infant with UTD diagnosed antenatally 


    Timing of postnatal ultrasound

    • Indications for an early renal USS ( <48 hours):
      • Presence of red flags (to rule out urological emergencies)
      • UTD on second trimester scan without repeat scan in third trimester
    • An ultrasound performed before the infant is one week of life may not reflect the true extent of urinary tract dilation as neonatal urine output is still increasing
    • If normal, a repeat ultrasound should be done at 4-6 weeks to confirm the absence of urinary tract dilation

    Other investigations

    Other investigations, eg MAG3 scan, are not routinely required. Discuss with senior paediatrician or paediatric nephrologist/urologist  


    Prophylactic antibiotics for UTI prevention may be indicated:

    • Trimethoprim – 2 mg/kg once daily

    Parent education

    Discuss and provide written information to parents on symptoms of urinary tract infection in neonates

    Symptoms including fever, vomiting, decreased urine output and irritability suggest the need for UTI screening

    Consider consultation with local paediatric team when

    Any pregnancy where there is antenatal UTD or where there is an infant with UTD should be linked with the local paediatric team

    Discuss with paediatric nephrology/urology:

    • Poor urinary stream
    • Palpable bladder
    • Palpable kidney
    • Dilated ureter
    • Cortical thinning
    • Abnormal corticomedullary differentiation
    • Solitary kidney with urinary tract dilation
    • Oligohydramnios with urinary tract dilation (regardless of the cause)

    Consider transfer when

    Child requiring care beyond the comfort of the local health care facility

    For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

    Consider discharge when

    • Diagnosis clear
    • Management instituted
    • Follow up organised

    Parent information

    See parent resources

    Last updated December 2021

  • Reference List

    1. Baskin, L (2021). Postnatal management of fetal hydronephrosis, UpToDate. Retrieved April 28, 2021 from
    2. Hydronephrosis in neonates. Safer Care Victoria (2021). Retrieved August 7 2021 from
    3. Multidisciplinary consensus on the classification of prenatal and postnatal urinary tract dilation UTD Classification system. Hiep Nguyen et al. J of Ped Urology 2014 10,982-999
    4. Royal Womens Hospital Guideline: Antenatal Urinary Tract Dilatation – Postnatal Evaluation and Management 2021
    5. The Magnitude of Fetal Renal Pelvic Dilatation can Identify Obstructive Postnatal Hydronephrosis and Direct Postnatal Evaluation and Management. Douglas Coplen et al. J of Urology 2006