906 Does urinary tract dilation (UTD) diagnosis in the 2nd trimester persist in the 3rd trimester?

Abstract

To determine if 2nd trimester fetal urinary tract dilation (UTD) persists on re-assessment in the 3rd trimester. A retrospective cohort at a single tertiary care prenatal ultrasound unit from 01/17-05/19. We included singleton pregnancies diagnosed with unilateral or bilateral UTD who had ultrasound in the 2nd trimester (<28 weeks) and ultrasound follow-up in the 3rd trimester (≥28 weeks). The outcome was persistent UTD in the 3rd trimester (i.e., true positive). Diagnoses followed the 2014 UTD Classification System for renal pelvic dilation: A1< 28 weeks: ≥ 4mm, ≥ 28 weeks: ≥7mm; and A2-3< 28 weeks: ≥ 7mm, ≥ 28 weeks: ≥ 10mm, in addition to bladder and/or calyceal dilation. Of 26,620 2nd trimester ultrasounds, 347 patients had a diagnosis of 2nd trimester UTD with 3rd trimester follow-up. Almost all (99%, 344/347) patients had a UTD diagnosis with renal pelvic dilation in the 2nd trimester, 52% were bilateral, and 84% were A1 UTD. Less than half the patients (150/347) with 2nd trimester UTD had persistent 3rd trimester UTD with a true positive rate of 43% (95% CI: 38 to 49%). Of persistent 3rd trimester UTD cases, 98% (147/150) had renal pelvic dilation, 91% were bilateral, and 28% were A1 UTD. The mean renal pelvic dilation in the second trimester was higher on both the right (5.5 vs. 4.9 mm; p<0.01) and left side (5.8 vs. 4.9 mm; p=0.02) for patients with persistent 3rd trimester UTD. In the 2nd trimester, adjusting for gestational age at the time of assessment, bilateral renal pelvic dilation (48% vs. 38%; AOR: 1.52, 95% CI: 1.00 to 2.34), bladder and/or calyceal dilation (84% vs. 40%; AOR: 7.88, 95% CI: 2.24 to 27.73), and A2-3 severity (70% vs. 37%; AOR: 4.13; 95% CI: 2.18 to 7.81) predicted persistent UTD in the 3rd trimester. Nearly 3 in 5 patients diagnosed with UTD in the 2nd trimester will not have persistent UTD in the 3rd trimester. Consideration of laterality, non-pelvic dilation, and degree of dilation improves prediction of persistence. Refining risk factors for persistence may reduce unnecessary follow up for some 2nd trimester cases of UTD.