OBJECTIVE: To study the impact of the organisation of obstetric services on the regionalisation of care for very preterm births. DESIGN: Cohort study. SETTING: Ten European regions covering 490 000 live births. POPULATION: All children born in 2003 between 24 and 31 weeks of gestation. METHOD: The rate of specialised maternity units per 10 000 total births, the proportion of total births in specialised units and the proportion of very preterm births by referral status in specialised units were compared. MAIN OUTCOME MEASURE: Birth in a specialised maternity unit (level III unit or unit with a large neonatal unit (at least 50 annual very preterm admissions). RESULTS: The organisation of obstetric care varied in these regions with respect to the supply of level III units (from 2.3 per 10 000 births in the Portuguese region to 0.2 in the Polish region), their characteristics (annual number of deliveries, 24 hour presence of a trained obstetrician) and the proportion of all births (term and preterm) that occur in these units. The proportion of very preterm births in level III units ranged from 93 to 63% in the regions. Different approaches were used to obtain a high level of regionalisation: high proportions of total deliveries in specialised units, high proportions of in utero transfers or high proportions of high-risk women who were referred to a specialised unit during pregnancy. CONCLUSION: Consensus does not exist on the optimal characteristics of specialised units but regionalisation may be achieved in different models of organisation of obstetric services.