Revisiting the risk for aneuploidy in fetuses with isolated pyelectasis

Objective: Previous studies are contradictory with regard to the association of isolated pyelectasis and aneuploidy. Our objective was to test the hypothesis that isolated pyelectasis is associated with aneuploidy and calculate likelihood ratios using a large ultrasound database. Methods: A retrospective cohort study of pregnancies presenting to our prenatal ultrasound unit at 16 to 22 weeks was conducted. Pyelectasis was defined as fetal renal pelvis> 4 mm in the anterior-posterior dimension. Fetuses with co-existing major structural anomalies or markers of aneuploidy were excluded. Association between isolated pyelectasis and aneuploidy was assessed and screening efficiency was evaluated. Results were also stratified by maternal age. Results: Among 62 103 patients who had obstetric ultrasounds during the study period, 1055 (1.7%) were diagnosed with isolated pyelectasis. The presence of isolated pyelectasis was significantly associated with any aneuploidy [OR 1.93 (CI 1.06-3.54)], and specifically trisomy 21 (T21) [OR 2.91 (CI 1.48-5.71)]. There was a greater than two-fold increase in the risk of T21 in the presence of isolated pyelectasis [LR+ 2.44 (CI 1.28-4.64)]. Conclusions: Our data confirm a significant association between isolated pyelectasis and increased risk of aneuploidy, particularly T21. These likelihood ratios can be used to adjust aneuploidy risk and in counseling patients regarding appropriateness of amniocentesis.