Assessment of prenatal SHS exposure
SHS exposure after birth was assessed using self-reported questionnaires. Mothers were asked to complete the questionnaire at week 36 of pregnancy. They were considered to have been exposed to SHS if they answered “Yes” to the question: “Were you exposed to secondhand smoke during the period of this pregnancy?”. For quantitative assessment, urine cotinine levels of the pregnant mothers were measured at gestational week 36.