Outcomes in Infants with Unprovoked Venous Thromboembolism: A Retrospective Cohort Study

Background: Although children aged <1 year have a relatively high rate of venous thromboembolism (VTE) compared to older children, most have additional prothrombotic risk factors. Unprovoked VTE is rare, and little is known about this population, particularly the risk of recurrent VTE. Objectives: We aimed to determine the rate of recurrent VTE in infants with prior unprovoked VTE and evaluate long-term, end-organ outcomes for infants with renal and intracranial vein thrombosis. Methods: Infants <1 year of age with an unprovoked VTE between 2003 and 2021 at a single institution were included. Time to recurrent event and anticoagulation duration were summarized using the Kaplan-Meier estimator. Neurologic outcomes were summarized with the pediatric stroke outcome measure for infants with cerebral sinovenous, medullary, or cortical vein thrombosis. Kidney outcomes were summarized with estimated glomerular filtration rates for infants with renal vein thrombosis. Anticoagulation was summarized. Results: Forty infants with intracranial, renal, portal, and extremity VTE met the inclusion criteria and were followed for a median of 4.7 years (IQR, 2.1-8.5). Most VTE events occurred during the first month of life. There was 1 recurrent event in 237 person-years of follow-up (incidence rate, 4 per 1000 [95% CI, 0.6-29.9] person-years). In outpatient follow-up, 40% of infants with intracranial thrombosis met criteria for moderate or severe neurologic outcomes and two-thirds of infants with a prior renal vein thrombosis had abnormal kidney function (estimated glomerular filtration rate < 90 mL/min/1.73 m(2)). Conclusion: There is a low rate of recurrent VTE but significant end-organ morbidity in infants with unprovoked VTE.