Transfers of women planning birth in midwifery units: data from the birthplace prospective cohort study.

To examine the percentage of women transferred, reasons for transfer and factors associated with the transfer of women planning birth in midwifery units (MUs). Prospective cohort study. All freestanding midwifery units (FMUs) and alongside midwifery units (AMUs) in England. Twenty-nine thousand, two hundred and forty-eight eligible women with a singleton, term and 'booked' pregnancy, planning birth in an MU between April 2008 and April 2010. Multivariable logistic regression was used to explore the sociodemographic and clinical characteristics associated with transfer. Transfer during labour or within 24 hours of birth. Over one in four women were transferred from AMUs and over one in five from FMUs. In both types of MU, compared with multiparous women aged 25-29 years, nulliparous women aged <20 years had higher odds of transfer (FMU-adjusted odds ratio [OR], 4.5; 95% confidence interval [CI], 3.10-6.57; AMU-adjusted OR, 2.6; 95% CI, 2.18-2.06), and the odds of transfer increased with increasing age. Nulliparous women aged ≥ 35 years in FMUs had 7.4 times the odds of transfer (95% CI, 5.43-10.10) and, in AMUs, 6.0 times the odds of transfer (95% CI, 4.81-7.41). Starting labour care after 40 weeks of gestation and the presence of complicating conditions at the start of labour care were also independently associated with a higher risk of transfer. Transfer from MUs is common, especially for first-time mothers. This study provides evidence on the maternal characteristics associated with an increased risk of transfer, which can be used to inform women's choices about place of birth. © 2012 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2012 RCOG.