Abstract: Background: In Europe, the majority of healthy women give birth at conventional obstetric units with the assistance of registered midwives. This study examines the relationships between the intrapartum transfer of care (TOC) from midwife to obstetrician-led maternity care, obstetric unit size (OUS) with different degrees of midwifery autonomy, intrapartum interventions and birth outcomes. Methods: A prospective, multicentre, cross-sectional study promoted by the COST Action IS1405 was carried out at eight public hospitals in Spain and Ireland between 2016-2019. The primary outcome was TOC. The secondary outcomes included type of onset of labour, oxytocin stimulation, epidural analgesia, type of birth, episiotomy/perineal injury, postpartum haemorrhage, early initiation of breastfeeding and early skin-to-skin contact. A logistic regression was performed to ascertain the effects of studied co-variables on the likelihood that participants had a TOC; Results: Out of a total of 2,126 low-risk women, those whose intrapartum care was initiated by a midwife (1772) were selected. There were statistically significant differences between TOC and OUS (S1 = 29.0%, S2 = 44.0%, S3 = 52.9%, S4 = 30.2%, p < 0.001). Statistically differences between OUS and onset of labour, oxytocin stimulation, type of birth and episiotomy or perineal injury were observed (p = 0.009, p < 0.001, p < 0.001, p < 0.001 respectively); Conclusions: Findings suggest that the model of care and OUS have a significant effect on the prevalence of intrapartum TOC and the birth outcomes. Future research should examine how models of care differ as a function of the OUS in a hospital, as well as the cost-effectiveness for the health care system.