PURPOSE OF THE STUDY.
To examine the association of maternal passive smoking during pregnancy and wheezing in children up to 2 years.
The authors of this study included 15 cohorts in the European project Environmental Health Risks in European Birth Cohorts. The cohorts were recruited from 1990 to 2008. A total of 37 459 mother-child pairs were available, and 27 993 had complete data on secondhand smoke exposure and wheeze.
Active and passive smoke exposure was obtained from questionnaire data submitted by each cohort. Four exposure definitions were created: prenatal active smoking, prenatal passive smoking, …