Recruitment to ALSPAC was opportunistic and aimed to recruit women as early in pregnancy as possible. ALSPAC attempted to make contact with eligible women through media information encouraging study contact and recruitment staff visiting community locations. In parallel, routine antenatal and maternity health services were used to promote the study and distribute an ‘expression of interest’ card. Through returning this card, women were able to request further information on the study or to decline participation. Completed cards contained sufficient detail (address and EDD) to allow ALSPAC staff to determine eligibility. Women requesting further information were sent a study information booklet followed by an initial questionnaire ∼1 week later. Invitation cards indicated that study consent was ‘opt out’, i.e. women not actively declining participation would be included in future data collection follow-up.
