The KOALA Birth Cohort Study is a prospective cohort of over 2,800 pregnant women and their single birth children in the Netherlands. Over 2,300 conventional participants were recruited at 14 to 16 weeks gestation from an existing longitudinal study on pregnancy-related pelvic girdle pain. Additionally, over 490 alternative participants, who had alternative lifestyles in terms of dietary habits such as preferring organic food, vaccination programs, and/or antibiotic use, were recruited at 14 to 18 weeks gestation through several recruitment strategies, such as posters in organic shops and anthroposophical clinics.