EP06.15: Incidence of copy number variations in fetuses with isolated upper urinary tract dilatations

To evaluate the incidence of copy number variations (CNV) in fetuses with isolated upper urinary tract dilatations. Retrospective study including fetuses identified as low risk in first trimester combined screening, with upper urinary tract dilatation, from 2011 to 2024 that underwent amniocentesis with chromosomal microarray analysis (CMA). Data recorded included dilatation characteristics, anterior-posterior measurement of the renal pelvis (<28 weeks: mild 4 to 7mm, moderate 7 to 10mm, severe if exceeding 10mm; > 28 weeks: mild 7 to 10mm, moderate 10 to 15mm and severe above 15mm), stratification on prenatal obstructive risk (based on prenatal UTD Classification: low UTD A1 and high UTD A2-3), CMA results and postnatal outcomes. We included a total of 117 fetuses. Median gestational age at diagnosis was 22 weeks (16 -39), dilatations were unilateral (68%), in the right side (53%), males (71%); 44/117 (38%) were mild, 51/117 (44%) moderate and 22/117 (19%) severe. Calices were dilated in 79% and ureters in 39% of cases. Regarding mild dilatations, 18% progressed to moderate-severe, and 23% normalised in third trimester; while 89% of those diagnosed as severe remained until birth. 74% were stratified as UTD 2-3. CNV were diagnosed in 2 cases (1.7%), confined to moderate dilatations (3.9%): one microdeletion of 4p16.2associated to motor and cognitive delay which presented as moderate and unilateral at 18 weeks and progressed to severe, and one duplication of 16p11.2, associated to low weight, microcephaly, and neurodevelopmental delay, presented as bilateral, moderate at 27 weeks and continued stable. No CNV or structural anomalies were detected after birth in normal CMA fetuses. In moderated dilatations, the incidence of pathogenic variant of copy was higher than in general population (3.9%), so amniocentesis for CMA study in moderated and severe dilatations should be considered.