The OBS was launched in 2013 with pregnant women who were less than 17 weeks gestational age, recruited from antenatal clinics at Mount Sinai Hospital, Toronto, Canada. The collection of biological samples, clinical data, and questionnaire data has been incorporated into routine care, therefore the OBS is an open, longitudinal cohort with the intention to continue recruitment indefinitely. Phase 1 of recruitment was the initial 2-year pilot phase of the study that was launched in January 2013, and recruitment was completed in November 2015 (with births occurring up to May 2016). Within the baseline sample, 39% of mothers were 35 years of age or older, including 7% of women who were 40 years of age or older. Most of the parents identified as being White (of European descent; 69% of mothers and 72% of fathers), but there were other ethnicities represented, particularly Asian, consistent with the diverse Toronto population. There were 87% of women who reported that they were currently married, and most parents had completed university education (84% of mothers and 75% of fathers).

Recruitment is ongoing