Table 1.

OR for preterm birth per 10 μg/m³ increase in the first trimester O₃ and/or the first trimester NO_x levels

	N	OR	95% CI	n*	OR*	95% CI*
O3 unadjusted model	120745	1.03	1.01 to 1.06	100812	1.04	1.01 to 1.06
O3 model 2†	120251	1.04	1.01 to 1.07	100408	1.04	1.00 to 1.08
O3 model 3‡	120251	1.04	1.01 to 1.08	100408	1.09	1.03 to 1.16
O3 model 4§	120251	1.04	1.01 to 1.08	100408	1.07	1.02 to 1.12
O3 model 5¶	115148	1.05	0.99 to 1.11	95817	1.11	1.02 to 1.21
O3 model 6**	86983	1.04	0.98 to 1.10	73267	1.07	0.99 to 1.15
NOx unadjusted model	120745	0.99	0.98 to 1.01	100812	0.99	0.97 to 1.01
NOx model 2†	120251	1.00	0.98 to 1.02	100408	1.00	0.98 to 1.02
NOx model 3‡	120251	1.02	0.99 to 1.06	100408	1.04	0.99 to 1.08
NOx model 4§	120251	1.01	0.98 to 1.05	100408	1.03	0.99 to 1.07
NOx model 5¶	115148	1.02	0.99 to 1.06	95817	1.02	0.97 to 1.07
NOx model 6**	86983	1.01	0.97 to 1.06	73267	1.01	0.96 to 1.07

*Elective caesarean section deliveries were excluded from the analysis.

†Single pollutant model adjusted for maternal age, parity, level of education, area of origin, maternal asthma and season of conception.

‡Single pollutant model adjusted for everything in † and conception year.

§Multiple pollutant model adjusted for † and ‡.

¶Multiple pollutant model adjusted for †–§, first trimester temperature and first trimester relative humidity.

**Multiple pollutant model adjusted for †–¶, maternal smoking, family situation and BMI at the first antenatal care visit.