Fetal pyelectasis and Down syndrome: is genetic amniocentesis warranted?

An association between pyelectasis and Down syndrome has recently been reported. The purpose of this investigation was twofold: 1) to test the hypothesis that pyelectasis is more common in fetuses with Down syndrome, and 2) to determine whether genetic amniocentesis should be offered when dilated renal pelves are identified during fetal ultrasound examination. The study population of 5944 fetuses was separated into two groups by infant outcome: 1) phenotypically and/or chromosomally normal, and 2) chromosomally abnormal. Each group was examined for the presence of pyelectasis, defined as an anteroposterior renal pelvic diameter of 4 mm or greater before 33 weeks or 7 mm or greater after 33 weeks. Pyelectasis was observed in 17.4% (four of 23) of Down syndrome fetuses versus only 2% (120 of 5876) of normal controls, a statistically significant difference (P less than .001). The predictive value of pyelectasis for Down syndrome (one in 90) compares favorably with other accepted indications for genetic amniocentesis, such as advanced maternal age and low maternal serum alpha-fetoprotein (MSAFP). When fetuses with concomitant sonographic abnormalities were excluded, the predictive value of isolated pyelectasis fell to one in 340. We conclude that although renal pyelectasis is more common in Down syndrome fetuses, genetic amniocentesis should be reserved for those cases presenting other risk factors such as advanced maternal age, low MSAFP, or other sonographic abnormalities.