When should a neonate with prenatal pyelectasis undergo a repeat ultrasound after delivery?

From the Guidelines

A repeat ultrasound for a neonate with prenatal pyelectasis should be performed at 1 to 6 months after delivery, as this timing allows for the assessment of persistent hydronephrosis and guides further management. This recommendation is based on the most recent and highest quality study, which suggests that a follow-up ultrasound in 1 to 6 months is usually appropriate for neonates with an antenatal diagnosis of hydronephrosis and isolated mild (SFU grade 1 and 2) hydronephrosis on initial US 1.

The initial postnatal ultrasound should be delayed at least 48 to 72 hours after birth to account for physiologic changes, including the transition from fetal to neonatal renal function and clearance of maternal hormones that can affect urinary tract dilation 1.

Key considerations for the timing of the repeat ultrasound include:

• The severity of the prenatal pyelectasis
• The presence of underlying urologic abnormalities
• The risk of urinary tract infections
• The need for prophylactic antibiotics in moderate to severe cases

In general, a follow-up ultrasound in 1 to 6 months is a reasonable approach, as it allows for the assessment of persistent hydronephrosis and guides further management, including the potential need for additional imaging studies or prophylactic antibiotics 1.

It is essential to educate parents about signs of urinary tract infection, such as fever, irritability, and poor feeding, that would warrant immediate medical attention before the scheduled follow-up.

The American College of Radiology recommends a follow-up ultrasound in 1 to 6 months for neonates with an antenatal diagnosis of hydronephrosis, which supports this approach 1.

Ultimately, the decision on the timing of the repeat ultrasound should be individualized based on the specific clinical scenario and the presence of any underlying urologic abnormalities.

From the Research

Timing of Repeat Ultrasound for Neonates with Prenatal Pyelectasis

• The optimal timing for a repeat ultrasound in neonates with prenatal pyelectasis is not universally agreed upon, but several studies provide guidance on this issue 2, 3, 4, 5, 6.
• A study published in 1997 found that an RPD smaller than 10 mm on neonatal sonography was of no pathologic significance, and renal collecting systems normalized spontaneously in all infants within 1 year of birth 2.
• Another study published in 2013 suggested that prenatal anteroposterior pelvic diameter cutoffs can be used to predict significant nephron uropathy requiring surgery, and proposed cutoffs of 6 mm at 20 weeks of gestation and 10 mm at 30 weeks of gestation for isolated pyelectasis 3.
• A 2004 study found that two successive neonatal renal ultrasound examinations performed at day 5 and 1 month had a high sensitivity and negative predictive value for predicting significant nephrouropathies, and suggested that infants with normal neonatal renal ultrasound scans may not require further evaluation 4.
• More recent studies have also investigated the postnatal outcomes of fetuses with prenatal diagnosis of pyelectasis, and found that most cases of mild pyelectasis remain stable or resolve spontaneously during pregnancy 5, 6.
• Based on these studies, it appears that a repeat ultrasound can be performed at various time points, including:
  • Day 5 after birth 4
  • 1 month after birth 4
  • 6 months after birth 3
  • 1 year after birth 2
• However, the specific timing of the repeat ultrasound may depend on the severity of the pyelectasis and the presence of other risk factors or symptoms.