TABLE 1

Register Variables in the Study

VariablesNational RegisterDefinitions
OutcomeAny asthma medicationSwedish Prescribed Drug RegisterAt least 1 purchase of a prescribed drug with an ATC code starting with R03 in 2006
Inhaled ICSSwedish Prescribed Drug RegisterAt least 1 purchase of a prescribed drug with an ATC code starting with ATC codes of R03AK or R03BA in 2006
Maternal/paternal asthmaAsthmaSwedish Prescribed Drug RegisterAt least 1 purchase of a prescribed drug with an ATC code starting with R03 in 2006
PerinatalGestational ageSwedish Medical Birth RegisterAccording to ultrasound measures in early pregnancy (week 10–18) in 70.1% and maternal report of last menstrual period in the remaining. Categorized into extremely preterm (week 23–28), very preterm (week 29–32), and moderately preterm (week 33–36, when possible divided into week 33–34 and week 35–36), early-term (week 37–38), term (week 39–41), and postterm (weeks 42–45)
SGASwedish Medical Birth RegisterLess than −2 SDs according to the scale created by Marsál et al14 based on intrauterine ultrasound measures
Cesarean deliverySwedish Medical Birth RegisterCategorized into yes or no
Multiple birthSwedish Medical Birth RegisterCategorized as no if singleton, all others as yes
Low Apgar scoreSwedish Medical Birth RegisterApgar score ≤7 at 5 min
ChorioamnionitisSwedish Medical Birth RegisterMaternal diagnosis at birth of O41.1 (ICD-10)
Maternal smokingSwedish Medical Birth RegisterInformation routinely collected by midwife at the first visit to the maternity health clinic after 8 to 12 weeks' gestation. Categorized into no, 1–9 cigarettes/d, ≥10 cigarettes/d, and missing
RSVSwedish Hospital Discharge Register 1987–2005At least 1 discharge with a diagnosis of J12.1 or J20.5 (ICD-10) before 12 months of age
SociodemographicMaternal educationSwedish National Education RegisterHighest formal education attained by each individual up to 2005. If the mother was no longer a Swedish resident, we replaced with paternal education if possible. Categorized by years of education into ≤9 years, 10 to 12 years, 13 to 14 years, ≥15 years, and missing
Maternal ageSwedish Medical Birth RegisterCategorized in years into 12 to 19, 20 to 24, 25 to 29, 30 to 34, 35 to 39, and ≥40
Social assistanceTotal Enumeration Income survey of 2005Cash income allowance from local social authorities after a thorough means investigation with the purpose to guarantee the applicant a minimum standard of living
  • ICD-10 indicates International Classification of Diseases, 10th Revision.