The association between fetal pyelectasis on second trimester ultrasound scan and aneuploidy among 25 586 low risk unselected women

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Abstract
Objective To determine the association of fetal pyelectasis FP found at the time of second trimester detailed ultrasound scan with aneuploidy in an unselected low‐risk population. Design Retrospective study of ultrasonographic reports, films and hospital notes over an eight‐year period from 1991 to 1998. Setting District general hospital obstetric department with 3500 deliveries annually serving a low‐risk cosmopolitan population. Main Outcome Measure The prevalence of aneuploidy in cases of fetal pyelectasis. Methods The obstetric ultrasound reports and films of 29591 cases were reviewed to identify those with FP at their detailed anomaly scan between 18 and 24‐weeks gestation. The study sample included women whose scan showed the fetal renal pelvis of either kidney to be five millimetres or more in the anteroposterior diameter. Demographic data and other ultrasonographic abnormalities were noted. The genotype and phenotype of the babies were traced from a combination of cytogenetic reports and paediatric notes. Results There were 320 cases of FP among the 25586 low‐risk study population available in the studied gestational period (18–24 weeks) giving a prevalence of 1.25 percent. Of these, 301 cases of FP were found in isolation and 19 were found in association with another ultrasonographic marker. None of the 315 cases delivering at the Northwick Park & St. Mark's Hospital had aneuploidy. Pyelectasis was more likely to be bilateral (57%), and more in male fetuses (72%). The mean diameter for the pyelectasis at diagnosis was 6.5 mm (1.4 SD) ranging between 5 and 15 mm. One hundred and thirty seven cases (43%) resulted in spontaneous resolution. Conclusion The prevalence of FP at the anomaly scan in an unselected low‐risk population is not high (1.25%). Our data suggest that the risk of aneuploidy associated with isolated FP in a low‐risk, unselected population is so small that it should not be an indication for invasive prenatal karyotyping. Copyright © 2002 John Wiley & Sons, Ltd.