Pregnancy and Birth > Ultrasound > Common Ultrasound Findings >Pylectasis                                   en Español
 Fetal Pyelectasis (Pelviectasis)
Enlargement of the part of the kidney that collects urine (the renal pelvis) from 4 to 10 millimeters in diameter is called fetal pyelectasis or “renal pelvic dilatation”. Dilation of the renal pelvis to greater than 10 mm is called severe pyelectasis or hydronephrosis. The illustration at right shows a normal kidney compared to a kidney with pyelectasis.

   Normal Pyelectasis

Pyelectasis is detected in 1 per 100 babies before birth, and is seen more commonly in male fetuses [14].  About 1 in 500 cases develops significant disease. Most mild cases resolve before  birth or within a few months after delivery [1,2].

A fetus with severe pyelectasis or hydronephrosis is at increased risk of developing problems such as low amniotic fluid and kidney disease. In addition pyelectasis has a weak association with chromosome abnormalities, in particular Down syndrome [3,4]. The severity of isolated pyelectasis does not appear to increase the risk for chromosome abnormality [5].

What Causes It?

The most common causes of severe pyelectasis or hydronephrosis are a blockage of the ureter (the tube that carries urine from the kidney to the bladder) where it joins the kidney and backward flow of urine from the bladder (vesicoureteric reflux) [6]. Less common causes of hydronephrosis include posterior urethral valves, urethral atresia, ectopic ureteroceles, duplication of the collecting system, megacystis-microcolon-intestinal-hypoperistalsis syndrome, prune belly syndrome, and cloacal malformation.

Does Pyelectasis Need Treatment?

Pylectasis involving only one kidney does not need intervention, but requires followed up ultrasound evaluation after 28 weeks for possible worsening of the condition.  Severe hydronephrosis involving both kidneys is associated with increased risk of poor outcome, and is monitored for the development of low amniotic fluid [11].

An ultrasound is usually done 5 to 7 days after birth to reevaluate the infant’s kidneys. Most cases of mild pyelectasis where the renal pelvis measures less than 8 mm and involves only one kidney tend to resolve spontaneously either in utero or within a few months after delivery.  Pyelectasis greater than 8 mm is more likely to need surgical correction during childhood [7-10].

What are the Chances of Having Pyelectasis Again in a Future Pregnancy?

In a study of 64 women with the finding of pyelectasis in their fetuses, 43 (67%) had a recurrence of this finding in their next pregnancy [15].

What is the Risk of Down Syndrome in a Fetus with Pyelectasis?

Presently genetic testing of the fetus (amniocentesis) is offered if the risk of Down syndrome in the fetus is ~ 1 in 200 or greater. For a 34 year old woman the isolated finding of pyelectasis at midtrimester increases the risk of Down syndrome from 1 in 365 to 1 in 192.

For a woman 34 years of age or less with a normal triple marker screen for Down syndrome the risk benefit ratio does not favor amniocentesis when the only ultrasound finding is pyelectasis [12,13].


1. Bianci D, Crombleholme T, D'Alton M. Fetology: Diagnosis and Management of the Fetal Patient. New York, NY: McGraw-Hill; 2000.
2. Mouriquand PD, Whitten M, Pracros JP. Pathophysiology, diagnosis and management of prenatal upper tract dilatation. Prenat Diagn. 2001;21:942-951
3 . Smith-Bindman R, et al. Second-trimester ultrasound to detect fetuses with Down's syndrome. JAMA 2001;285:1044-55
4. Chudleigh PM, The association of aneuploidy and mild fetal pyelectasis in an unselected population: the results of a multicenter study. Ultrasound Obstet Gynecol. 2001 ;17:197-202.
5.Roshanfekr D, Vonpechman W, Petrikovsky B Severity of isolated fetal pyelectasis and risk of aneuploidy. Obstet Gynecol 2000;95(4 Suppl 1):S72
6. Marra G, Barbieri G, Moioli C, Assael BM, Grumieri G, Caccamo ML. Mild fetal hydro-nephrosis indicating vesicoureteric reflux. Arch Dis Child Fetal Neonatal Ed 1994; 70: F147-F150.
7. Ahmad G, Outcome of fetal pyelectasis diagnosed antenatally.
J Obstet Gynaecol. 2005 ;25:119-22.
8. Cohen-Overbeek TE, Mild renal pyelectasis in the second trimester: determination of cut-off levels for postnatal referral. Ultrasound Obstet Gynecol. 2005 ;25:378-83.
9. Adra AM, Fetal pyelectasis: is it always "physiologic"? Am J Obstet Gynecol. 1995 ;173:1263-6.
10. Sairam S, Natural history of fetal hydronephrosis diagnosed on mid-trimester ultrasound. Ultrasound Obstet Gynecol. 2001;17:191-6.
11. Flake AW, Ureteropelvic junction obstruction in the fetus. J Pediatr Surg. 1986;21:1058-63.PUBMED
12. Havutcu AE,et al. The association between fetal pyelectasis on second trimester ultrasound scan and aneuploidy among 25,586 low risk unselected women. Prenat Diagn. 2002 ;22:1201-6.
13.Corteville et al.. Fetal Pyelectasis & Down Syndrome: Is Genetic Amniocentesis Warranted? Obstet Gynecol 1992; 79:770-2
14.Wax JR, et al.  Does the frequency of soft sonographic aneuploidy markers vary by fetal sex? J Ultrasound éd. 2005 Aug;24(8):1059-63 PMID: 16040819
15. Degani S, et al. Fetal pyelectasis in consecutive pregnancies: a possible genetic predisposition Ultrasound Obstet Gynecol. 1997 Jul;10(1):19-21. PMID: 9263418


Home | About | Disclaimer | Privacy | Contact

Copyright © 2005-2013 by Focus Information Technology. All rights reserved.