Fransen 2017.

Study characteristics
Methods	Cluster‐randomised controlled trial comparing simulation‐based obstetric team training versus no intervention.
Participants	All employed multi‐professional obstetric staff members of included units: 471 (intervention) versus 503 participants (control). In the intervention group there were 14,500 singleton pregnancies (beyond 24 weeks of gestation) studied, and in the control group 14,157.
Interventions	1‐day simulation‐based obstetric team training in a simulation centre versus no intervention. Training content: crew resource management and medical technical skills (shoulder dystocia, postpartum haemorrhage, umbilical cord prolapse, eclampsia and resuscitation of a pregnant woman).
Outcomes	Primary outcome: composite outcome of obstetric complications during the first year post‐intervention, including low Apgar score, severe postpartum haemorrhage, trauma due to shoulder dystocia, eclampsia and hypoxic‐ischaemic encephalopathy. Maternal and perinatal mortality were also registered.
Notes	Multicentre trial including 24 hospitals, the Netherlands. Study period: 2009‐2011.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computerised randomisation (computer‐generated list) by an independent researcher.
Allocation concealment (selection bias)	Low risk	All cluster‐trials were randomised at once by an independent researcher using a computerised, stratified randomisation.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants were not blinded to the intervention, probably low impact on chosen outcome measures.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "As this was an open randomised trial, no one involved in the study was blinded to the allocation."
Incomplete outcome data (attrition bias) All outcomes	Low risk	No clusters were loss to follow‐up. Data collection was checked with national database.
Selective reporting (reporting bias)	Low risk	Quote: "The adjustment of the outcome measure was made before analysis. The original definition was added as a secondary outcome measure." Comment: probably no selective data reporting.
Other bias	Low risk	Clustering effect has been taken into account. Baseline imbalances were reported and an additional pre‐intervention measurement was added as a covariate in the analyses.