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Soft Markers
Fetal pyelectasis

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Dilatation of the fetal renal pelvis in AP diameter 5-10 mm, with no calyceal involvement.


The renal pelvis connects the renal calyces and ureter. By 16 weeks the amniotic fluid consists of fetal urine reflecting a functional renal system. Dilatation may reflect a downstream obstruction or intrinsic laxity in the collecting system and is often a variant of normal.

Standard image for identification/exclusion

A transverse section of the fetal abdomen should be obtained and one kidney identified in cross section. The transducer should be rotated through 90° to obtain a longitudinal section and the appearance of the renal pelvis should be noted. Dilated renal calyces should be looked for; if present these are confluent with the renal pelvis. The finding of dilated calyces, renal pelvis dilatation exceeding 10 mm or ureteric dilatation are usually abnormal and warrant a detailed ultrasound scan with or without tertiary referral.

Technique for measurement/assessment

The maximum AP diameter of the kidney and renal pelvis should be made in the transverse plane. The fetal bladder and liquor volume should also be examined.
The ultrasound assessment should be completed, looking in particular for the other soft markers: nuchal pad, echogenic bowel, echogenic foci, short femur length and choroid plexus cysts.

Implication of a positive finding in isolation

Fetal pyelectasis may indicate urinary tract obstruction, vesico-ureteric reflux (Reference1)or normal variant. It may be an early sign of fetal hydronephrosis or be a marker for abnormalities such as renal duplication or reflux, which cannot be demonstrated by ultrasound antenatally. However, fetal pelvic dilatation is more common in the presence of maternal pelvic dilatation (Reference2)and may reflect a common locally acting factor rather than a distinct pathology.

There is a weak association with trisomy 21 in conjunction with other markers, but in isolation no further action is required.

In the absence of associated abnormalities, a third trimester ultrasound should be performed followed by postnatal ultrasound at least 3-4 days after birth, repeated at between one to three months of age (Reference3)and paediatric follow up.

Image 5 - Fetal pyelectasis



1. Stamillo DM, Morgan MA. Diagnosis of fetal renal anomalies. Obstet Gyn Clin N Am 1998; 25:527-52, Abstract

2. Graif M, Kessler A, Hart S, Daitzchman M, Mashiach S, Boichis H, Itzchak Y. Renal pyelectasis in pregnancy: correlative evaluation of fetal and maternal collecting systems. Am J Obstet Gynecol 1992; 167: 1304-6, Abstract

3. Langer B. Fetal pyelectasis. Ultrasound Obstet Gynecol 2000; 16:1-5, Abstract


© Perinatal Institute 2011