What are the next steps if an ultrasound detects an abnormal finding or concern, referred to as UTD (Uterine Tone Dysfunction), in a fetus?

Management of Fetal Urinary Tract Dilation (UTD) on Ultrasound

For fetuses with UTD detected on ultrasound, management should follow a risk-stratified approach based on the UTD classification system, with UTD A1 requiring follow-up ultrasound at ≥32 weeks gestation and UTD A2-3 requiring serial ultrasounds every 4 weeks with planned postnatal follow-up. 1

Understanding UTD Classification

UTD (Urinary Tract Dilation) is detected in 1-2% of pregnancies and uses a standardized classification system:

• UTD A1 (Low Risk):

  • Anterior-posterior renal pelvis diameter (APD) 4-7 mm at <28 weeks gestation
  • APD 7-10 mm at ≥28 weeks gestation
  • No calyceal dilation, normal parenchyma, no ureteral dilation, normal bladder

• UTD A2-3 (Increased Risk):

  • APD >7 mm at <28 weeks gestation
  • APD >10 mm at ≥28 weeks gestation
  • OR presence of calyceal dilation, abnormal parenchyma, ureteral dilation, abnormal bladder, or unexplained oligohydramnios 1

Management Algorithm for Fetal UTD

Initial Detection of UTD:

1. Risk Stratification:

   • Classify as UTD A1 (low risk) or UTD A2-3 (increased risk) based on ultrasound findings 1
   • Consider aneuploidy screening if not previously done 1

2. For UTD A1 (Low Risk):

   • Schedule follow-up ultrasound at ≥32 weeks gestation
   • If resolved at follow-up: no postnatal follow-up needed
   • If persistent at follow-up: plan for postnatal evaluation 1

3. For UTD A2-3 (Increased Risk):

   • Schedule serial ultrasound assessments every 4 weeks
   • Arrange specialty consultation with pediatric urology and/or nephrology
   • Plan for comprehensive postnatal follow-up 1

Aneuploidy Considerations:

• UTD is associated with a slight increased risk of trisomy 21 (positive LR of 1.5) 1, 2
• For patients with no previous aneuploidy screening and isolated UTD:
  • Recommend counseling about trisomy 21 risk
  • Discuss options for cell-free DNA screening or quad screen 1
• For patients with negative serum or cfDNA screening results and isolated UTD:
  • No further aneuploidy evaluation needed 1

Postnatal Evaluation Plan

For infants with prenatal UTD:

1. Timing of First Postnatal Ultrasound:

   • Perform renal and bladder ultrasound (RBUS) after 48 hours of life
   • Avoid ultrasound during first 48 hours as it may underestimate dilation due to physiologic neonatal third spacing 1

2. Additional Imaging Based on Risk:

   • For persistent UTD: Consider voiding cystourethrography (VCUG) to evaluate for vesicoureteral reflux (VUR)
   • For severe cases: Consider functional renal imaging (renal scintigraphy) 1

3. Specialist Involvement:

   • Pediatric urology and/or nephrology consultation for persistent or severe UTD 1, 3

Common Pathologic Causes of UTD

When persistent, UTD may indicate:

• Vesicoureteral reflux (most common)
• Ureteropelvic junction obstruction
• Ureterovesical junction obstruction
• Multicystic dysplastic kidneys
• Posterior urethral valves 1, 2

Important Clinical Considerations

• Approximately 80% of second-trimester UTD cases between 4-7 mm resolve spontaneously 1, 2
• The first postnatal ultrasound serves as a determinant of risk; higher levels of dilation correspond with higher need for surgery 1
• VUR occurs in approximately 15% of children with prenatally diagnosed isolated UTD 1
• Parental counseling should be provided by a multidisciplinary team including maternal-fetal medicine specialists and pediatric urology/nephrology providers 3

Common Pitfalls to Avoid

• Don't perform postnatal ultrasound too early: Ultrasounds during the first 48 hours of life may underestimate the degree of dilation 1
• Don't assume normal postnatal US excludes reflux: The risk of VUR in patients with a nondilated or mildly dilated collecting system may be as high as 25% 1
• Don't confuse UTD with uterine tone dysfunction: UTD refers specifically to urinary tract dilation, not uterine issues 4, 5
• Don't overreact to mild UTD: Most cases of mild UTD (UTD A1) resolve spontaneously and represent normal variants 1, 2