Renal pyelectasis literally means “pelvis dilation” of the kidney, and is defined as an anteroposterior diameter of the renal pelvis of ≥ 4mm up to 20 weeks of gestation.
When seen in isolation, with no other fetal abnormalities
If other anomalies are detected
Renal pyelectasis is reported in 0.6-4.5% of fetuses in the second trimester. It is most commonly a transient physiologic state in which the renal pelvis, the structure that is essentially the funnel for urine exiting the kidney into the ureter, is dilated and measures larger than what is considered normal for a particular gestational age. The presence of renal pyelectasis as an isolated finding, in the setting of a negative aneuploidy screen, is not itself an indication for invasive testing; however, ACOG does give all women the option (both high and low risk) for invasive testing. Note, if the renal pelvis is still dilated in the third trimester, the urinary tract may require attention following delivery to ensure normal kidney function and prevent infection in the newborn.
Multidisciplinary consensus on the classification of prenatal and postnatal urinary tract dilation (UTD classification system)
ACOG Practice Bulletin No. 162: Prenatal Diagnostic Testing for Genetic Disorders
ACOG Practice Bulletin No. 226: Screening for Fetal Chromosomal Abnormalities
Identification of copy number variations among fetuses with ultrasound soft markers using next-generation sequencing
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