Stec 1993.

Methods	Double‐blinded randomised controlled trial. Single‐centre: St. Peter's Medical Center Intensive Care Nursery, New Brunswick, New Jersey, USA, between 1 June 1 1987 and 30 August 30 1989.
Participants	42 inborn newborns (19 in the heparin group, 23 in the control group) with birth weight < 2000 grams, requirement for umbilical artery catheterisation and informed consent obtained from the parents. Gestational age and birth weight were similar in the two groups, i.e. 28 weeks ± 3 and 1096 ± 350 grams in the heparin group and 28 weeks ± 3 and 1000 ± 415 grams in the control group.
Interventions	Intervention group: flush solution (5% dextrose/0.2 normal saline) with 1 unit of heparin per mL. Control group: same flush solution without heparin.
Outcomes	Primary outcome: GM‐IVH. Secondary outcomes: severe IVH; complications of the umbilical artery catheters (hypertension, color changes of the extremities, and clotting of the catheter); need for respiratory support; pneumothorax; acidosis; sepsis; need for volume expanders; platelet count; death.
Notes	Lack of power of the study.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Infants were randomised by a random number table.
Allocation concealment (selection bias)	Unclear risk	No information provided.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	The flush solutions were prepared by the hospital pharmacy and the vials' contents were unknown to the clinical staff caring for the infants.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The ultrasound studies were reviewed by a paediatric radiologist or a neuroradiologist who were unaware of the infants' clinical course.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Outcomes reported for all randomised infants (no drop‐outs).
Selective reporting (reporting bias)	Unclear risk	The trial was not registered and no protocol was available. We could not ascertain if there were deviations from the original protocol in the final publication.
Other bias	Low risk	Appears free of other bias.