BACKGROUND: Midwifery units offer care to women with straightforward pregnancies, but unforeseen complications can arise during labour or soon after birth, necessitating transfer to a hospital obstetric unit. In England, 21% of women planning birth in freestanding midwifery units are transferred; in alongside units, the transfer rate is 26 There is little high quality contemporary evidence on women's experience of transfer. METHODS: We carried out a qualitative interview study, using semi-structured interviews, with women who had been transferred from a midwifery unit (freestanding or alongside) in England up to 12 months prior to interview. Maximum variation sampling was used. Interviews with 30 women took place between March 2009 and March 2010. Thematic analysis using constant comparison and exploration of deviant cases was carried out. RESULTS: Most women hoped for or expected a natural birth and did not expect to be transferred. Transfer was disappointing for many; sensitive and supportive care and preparation for the need for transfer helped women adjust to their changing circumstances. A small number of women, often in the context of prolonged labour, described transfer as a relief. For women transferred from freestanding units, the ambulance journey was a "limbo" period. Women wondered, worried or were fearful about what was to come and could be passive participants who felt like they were being "transported" rather than cared for. For many this was a direct contrast with the care they experienced in the midwifery unit. After transfer, most women appreciated the opportunity to talk about their experience to make sense of what happened and help them plan for future pregnancies, but did not necessarily seek this out if it was not offered. CONCLUSIONS: Transfer affects a significant minority of women planning birth in midwifery units and is therefore a concern for women and midwives. Transfer is not expected by women, but sensitive care and preparation can help women adjust to changing circumstances. Particular sensitivity around decision-making may be required by midwives caring for women during prolonged labour. Some apparently straightforward changes to practice have the potential to make an important difference to women's experience of ambulance transfer.