Sample selection
Women recruited for the survey were those who had straight-
forward pregnancies and satisfied the eligibility criteria developed
by the Trust for birth centre care summarised in Box 2 and set out
in detail in the Trust clinical guidelines.
It was assumed that women who live nearest would be the main
users of the facilities at the birth centre so we therefore recruited
women who were registered with general practices in the local areas
of Stepney and Bow and those who had booked to deliver at the birth
centre. As there was no single key comparison which could have
been used to calculate a sample size, it was based on practical
considerations, including the availability of funding. Past data from
the local child health system were used to estimate the numbers of
pregnant women living in the area who would satisfy the criteria for
birth centre care. On this basis, we planned to recruit up to 350
women for the pre-implementation survey and up to a further
350 fo rthe second survey after the birth centre opened. As there
was insufficient funding for a sample of this size in the Phase 1
pre-implementation survey, which was funded from a separate
source,the sample size was restricted to 250.