Objective: Longitudinal studies on cohorts of babies enrolled at birth are ongoing in Europe. On the basis of these experiences, a birth cohort study should be implemented in Italy at a national level. A pilot study is ongoing in Rome, from which we report data on adherence at recruitment and follow-up.
Design: Prospective cohort study.
Setting: the birth cohort was enrolled between June 2003 and October 2004, in two hospital ofRome in the district ofthe Local Health Unit RME.
Participants: we enrolled children of women older than 18 years, Italian citizens and residents in the Local Health Unit RME.
Main outcome measures: Baseline characteristics of enrolled women were compared with those of refusals, and characteristics of children with a complete follow-up with those lost at follow-up. Prevalence Rate ratio (PR) and the relative 95% confidence interval were calculated.
Results: The cohort consisted of 704 women (54% of the contacted) and 719 children. A low level of instruction (PR 2.84), and a caesarean delivery (OR 1.41) were significantly associated with the refusal. After the enrolment 25 children were lost, 117 were partially followed-up and 577 had a complete follow-up until the 15 month visit. Mothers of children lost at follow-up were less instructed (PR 1.69) and smoked during pregnancy (PR 1.57).
Conclusions: During the enrolment and the follow-up of a birth cohort greater efforts must be done to avoid selection for the socioeconomic level of the family. Keeping a high response rate to follow-up is the only way to ensure a good level of internal validity.