Objective: To determine the risk factors associated with umbilical vascular catheter‐associated thrombosis.

Methods: All consecutive inborn infants with umbilical arterial (UAC) and/or umbilical venous catheters (UVC) inserted for more than 6 h duration were included in the study. Each infant was screened for thrombosis in the abdominal aorta and inferior vena cava by 2‐D abdominal ultrasonography within 48–72 h of insertion of umbilical vascular catheters. Subsequent serial scanning was performed at intervals of every 5–7 days, and within 48 h after removal of catheters.

Results: Upon removal of umbilical catheters, abdominal aortic thrombi were detected in 32/99 (32.3%) infants with UAC. Small thrombi were detected in the inferior vena cava of 2/49 (4.1%) infants with UVC (one of whom had both UAC and UVC). When compared with those who received only UVC (n = 18), infants who received either UAC alone (n = 68) or both UAC and UVC (n = 31) had significantly higher risk of developing thrombosis (odds ratio (OR): 7.6, 95% confidence interval (CI): 1.1, 325.5)). Logistic regression analysis of various potential risk factors showed that the only significant risk factor associated with the development of abdominal aortic thrombosis following insertion of UAC was longer duration of UAC in situ (for every additional day of UAC in situ, adjusted OR of developing thrombosis was: 1.2, 95% CI: 1.1, 1.3; P = 0.002).

Conclusion: Umbilical arterial catheter‐associated thrombosis was common. Umbilical arterial catheter should be removed as soon as possible when not needed. Upon removal of UAC, all infants should be screened for abdominal aortic thrombus by 2‐D ultrasonography.