Participants
Of 1537 enrolled women, 30 were excluded due to ineligibility.
The final sample comprised 1507 eligible women.
Exact response figures are not possible to calculate as hospitals
identified participants and mailed invitation packages
on behalf of the research team. This meant we were unable
to assess wrongly addressed mail, duplicate mailings,
returns to sender and mail-outs to non-eligible women.
Over 6000 invitation packages were distributed. If we
assume that 80–90% of invitations were correctly addressed
and mailed to eligible participants, we estimate the final
response fraction to be in the range of 28–31%. However,
this is a conservative estimate, and it may have been
higher. The mean gestation at enrolment was 15 weeks (SD
3.1, range 6–24 weeks).