BackgroundThere are limited data at a population level on the burden, risk factors, and long-term outcomes of neonatal renal vein thrombosis (nRVT). We conducted a population-based cohort study to understand the epidemiology and outcomes of nRVT over a 25-year period in Ontario.MethodsUsing linked administrative health databases, all hospitalized neonates ≤28 days born in Ontario between 1992 and 2016 with nRVT were identified. The primary outcome was to calculate the incidence of nRVT and trend over time in Ontario. We also determined the risk factors associated with nRVT as well as the risk of long-term outcomes after nRVT, including CKD, ESKD, all-cause mortality, and hypertension (HTN) compared with the healthy neonatal population without nRVT.ResultsThe annual incidence rate of nRVT was 2.6 per 100,000 live births (n=85). Presence of respiratory distress syndrome (OR, 8.01; 95% CI, 4.90 to 13.1), congenital heart disease (OR, 9.1; 95% CI, 5.05 to 16.4), central venous catheterization (OR, 3.9; 95% CI, 1.89 to 7.93), maternal preeclampsia (OR, 2.8; 95% CI, 1.6 to 4.79), and maternal diabetes (OR, 2.36; 95% CI, 1.36 to 4.07) conferred the highest risk for nRVT. Over a median follow-up of 15 years and after adjusting for confounders, neonates with nRVT versus the comparator cohort had a 15.5-fold risk of CKD, HTN, or death (n=49 [58%] versus n=90,050 [3%]; 95% CI, 11.7 to 20.6); 12.3-fold increased risk of CKD or death (n=39 [46%] versus n=32,016 [1%]; 95% CI, 8.9 to 16.8); and a 15.7-fold increased risk of HTN (n=33 [39%] versus n=64,458 [2%]; 95% CI, 11.1 to 21.1). None of the nRVT cohort developed ESKD. The median time to composite outcome of CKD, HTN, or death was 11.1 years.ConclusionsPatients with a history of nRVT remain at higher risk than the general population for long-term morbidity or mortality, indicating the need for long-term follow-up.