Study design
The COCOA is a general population-based prospective birth cohort study designed to assess the impact of environmental exposure on allergic diseases(11). Regularly scheduled follow-ups to the physician’s office and self-reported questionnaires, laboratory examinations, and physical examinations were conducted at 36 weeks of gestation, birth, 6 months, 1 year, and then annually thereafter. Mothers completed a modified version of the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire(12). Of the 3,004 pairs, 2,360 (78.56%) were analyzed (Fig.1) in this study. A total of 1,405 and 659 children were followed up until the ages of 3 and 7, respectively.