OBJECTIVES: to identify factors associated with maternal intrapartum transfer from a freestanding birth centre to hospital. DESIGN: case-control study with retrospective data collection. PARTICIPANTS AND SETTINGS: cases included all 111 women transferred from a freestanding birth centre in Sao Paulo to the referral hospital, from March 2002 to December 2009. The controls were 456 women who gave birth in the birth centre during the same period who were not transferred, randomly selected with four controls for each case. METHODS: data were obtained from maternal records. Factors associated with maternal intrapartum transfers were initially analysed using a χ(2) test of association. Variables with p<0.20 were then included in multivariate analyses. A multiple logistic regression model was built using stepwise forward selection; variables which reached statistical significance at p<0.05 were considered to be independently associated with maternal transfer. FINDINGS: during the study data collection period, 111 (4%) of 2,736 women admitted to the centre were transferred intrapartum. Variables identified as independently associated factors for intrapartum transfer included nulliparity (OR 5.1, 95% CI 2.7-9.8), maternal age ≥35 years (OR 5.4, 95% CI 2.1-13.4), not having a partner (OR 2.8, 95% CI 1.5-5.3), cervical dilation ≤3 cm on admission to the birth centre (OR 1.9, 95% CI 1.1-3.2) and between 5 and 12 antenatal appointments at the birth centre (OR 3.8, 95% CI 1.9-7.5). In contrast, a low correlation between fundal height and pregnancy gestation (OR 0.3, 95% CI 0.2-0.6) appeared to be protective against transfer. CONCLUSIONS AND IMPLICATIONS FOR PRACTICE: identifying factors associated with maternal intrapartum transfer could support decision making by women considering options for place of birth, and support the content of appropriate information about criteria for admission to a birth centre. Findings add to the evidence base to support identification of women in early labour who may experience later complications and could support timely implementation of appropriate interventions associated with reducing transfer rates.