Methods
This prospective cohort study took place in a large
Dublin maternity hospital between November
2010 and December 2011. The hospital booked
more than 9500 women for maternity care in 2010.
Women were eligible to participate if they had a
singleton pregnancy, were aged 18 years or over
and understood English. Women were excluded
from recruitment into the study for the followingreasons: multiple pregnancy, language barrier,
illiteracy, late booking, or if they knew they would
not give birth in the study site.
The aim of recruitment was to invite every
eligible woman to participate in the study;
however, due to resource limitations and the range
of settings for booking visits, a pragmatic approach
was used by the research staff to recruit from
settings that had the greatest numbers of women
booking on a given day. An initial sample size of
1000 participants was planned, based on analyses
from a previous study of alcohol exposure during
pregnancy (Murphy et al, 2013a).
Data were collected in three phases; firstly at
the booking visit by a structured interview, and
secondly, during the third trimester of pregnancy
by a self-administered postal questionnaire. The
sample size was inflated to 1300 when a lower
response rate to the third trimester questionnaire
became apparent. Finally, data were collected
on the birth and postnatal period up until first
hospital discharge.