Table 2

ORs for preterm birth among non-asthmatic and asthmatic mothers per 10 μg/m3 increase in the first trimester O3 levels

GroupOR95% CIOR*95% CI*
O3 unadjusted modelNon-asthmatic1.031.01 to to 1.05
O3 unadjusted modelAsthmatic1.071.01 to to 1.16
O3 model 2†Non-asthmatic1.041.00 to to 1.15
O3 model 2†Asthmatic1.081.01 to to 1.24
O3 model 3‡Non-asthmatic1.041.00 to to 1.11
O3 model 3‡Asthmatic1.081.01 to to 1.21
O3 model 4§Non-asthmatic1.050.99 to to 1.21
O3 model 4§Asthmatic1.081.00 to to 1.29
O3 model 5¶Non-asthmatic1.040.98 to to 1.15
O3 model 5¶Asthmatic1.040.96 to to 1.20
  • *Elective caesarean section excluded from the analysis.

  • †Adjusted for maternal age, parity, level of education, area of origin, maternal asthma, conception year and season of conception.

  • ‡Adjusted for † and first trimester NOx.

  • §Adjusted for † and ‡ and first trimester temperature and relative humidity.

  • ¶Adjusted for †–§, maternal smoking, family situation and BMI at the first antenatal care visit.