Background Incorrect umbilical venous and arterial catheter (UAC and UVCs) tip position is associated with increased rate of complications.

Objective To determine whether using birth-weight (BW), rather than body surface measurement (M), to estimate ID of UVC and UACs results in more correctly placed catheters.

Methods Newborns undergoing UVC and/or UAC insertion were randomised to have ID estimated using BW [UVC: cm = (BW x 1.5) + 5; UAC: cm = (BW x 3) +9] or using shoulder to umbilicus measurement (M). The primary outcome was correct catheter tip position on X-ray (UVC T9–T10; UAC T6–T10).

Results We enrolled 101 newborns. UVC insertion was successful in 97 (96%). There was no difference in correctly placed UVCs between groups (Table). UAC insertion was attempted in 87 infants and was successful in 62 (71%). More infants in the W group had a catheter tip in the correct position (Table). We found no differences in secondary outcomes.

Conclusions UVCs often cannot be advanced to the estimated ID or are in the portal venous system on X-ray. Estimating UVC ID using BW did not result in more correctly placed UVCs. When successful, estimating UAC ID using BW results in more correctly placed catheters.