The association of aneuploidy and mild fetal pyelectasis in an unselected population: the results of a multicenter study

Introduction Mild pyelectasis is a common finding and there is some debate as to its association with aneuploidy. The results of a large, prospective, multicenter study of mild pyelectasis designed to determine the incidence and association with aneuploidy in an unselected population are reported. Methods A large multicenter, prospective observational study of unselected fetuses with mild pyelectasis identified between 16 and 26 weeks' gestation in routine ultrasound departments. Results There were 737 fetuses with mild pyelectasis of which 12 had an abn ormal karyotype. Pyelectasis was isolated in three fetuses with Down syndro me, but in one the mother was older (36 years). Conclusion These data confirm the fact that the presence of mild fetal pyel ectasis increases the risk for aneuploidy, in particular trisomy 21. Howeve r, other risk factors should be considered before embarking on fetal karyot yping, as for most pregnancies complicated by isolated mild pyelectasis, ri sks of aneuploidy will remain small.