Table 2.

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

	Group	OR	95% CI	OR*	95% CI*
O3 unadjusted model	Non-asthmatic	1.03	1.01 to 1.05	1.03	1.00 to 1.05
O3 unadjusted model	Asthmatic	1.07	1.01 to 1.14	1.09	1.02 to 1.16
O3 model 2†	Non-asthmatic	1.04	1.00 to 1.08	1.08	1.02 to 1.15
O3 model 2†	Asthmatic	1.08	1.01 to 1.15	1.14	1.05 to 1.24
O3 model 3‡	Non-asthmatic	1.04	1.00 to 1.08	1.06	1.01 to 1.11
O3 model 3‡	Asthmatic	1.08	1.01 to 1.15	1.12	1.04 to 1.21
O3 model 4§	Non-asthmatic	1.05	0.99 to 1.11	1.11	1.01 to 1.21
O3 model 4§	Asthmatic	1.08	1.00 to 1.17	1.16	1.04 to 1.29
O3 model 5¶	Non-asthmatic	1.04	0.98 to 1.10	1.07	0.99 to 1.15
O3 model 5¶	Asthmatic	1.04	0.96 to 1.14	1.09	0.98 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 NO_x.

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

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