Primary outcome Unassisted clinical maturation defined as: Use of fistula with 2 needles for 75% of dialysis sessions during a 4-wk period with either: 4 consecutive dialysis sessions with mean blood pump speed ≥ 300 ml/min, or Single-pool Kt/V ≥1.4 or urea reduction ratio >70% Criteria must be met without any fistula intervention procedures and by the later of 9 mo after surgery or 8 wk after dialysis initiation

Additional fistula use outcomes Assisted clinical maturation defined as clinical maturation following a maturation-facilitating procedure First cannulation attempt First successful cannulation defined as the use of the fistula with 2 needles and for the entire dialysis session Fistula durability defined as the number of months of use of the fistula for dialysis Fistula abandonment defined as the date at which the treating nephrologist or surgeon determines that the fistula will not be used in the future.

Anatomical (sonographic) outcomes Fistula blood flow rate Fistula artery diameter Fistula vein diameter Vein depth from skin surface Stenosis

Fistula events Thrombosis Hand ischemia infiltration Fistula bleeding Pseudoaneurysm or aneurysm requiring a procedure Infection

Fistula or other access procedures Angioplasty Surgical revision Stent placement Thrombolysis or thrombectomy Ligation of accessory veins Superficialization of vein Transposition of vein Central venous catheter placement Placement of new arteriovenous access

Clinical events Bloodstream infection Vascular access–related hospitalization Death