TABLE 6

Adjusted^# hazard ratios (HR) and 95% confidence intervals for the joint effects of maternal asthma and quartiles of particulate matter with a 50% cut-off aerodynamic diameter ≤2.5 μm (PM_2.5) exposure over specific periods of pregnancy on childhood asthma risk

Maternal asthma	PM_2.5 quartiles	Subjects n	Obstetric cases	HR (95% CI)	RERI (95% CI)
1st trimester					−0.06 (−0.16–0.03)
No	Q1	145 559	17 807	Ref.
No	Q2	143 670	19 323	1.00 (0.97–1.02)
No	Q3	139 399	20 506	1.03 (1.00–1.07)
No	Q4	139 781	21 964	1.06 (1.00–1.12)
Yes	Q1	10 162	1854	1.56 (1.49–1.64)
Yes	Q2	9218	1738	1.46 (1.39–1.54)
Yes	Q3	8531	1881	1.63 (1.54–1.73)
Yes	Q4	8140	1811	1.56 (1.45–1.67)
2nd trimester					−0.04 (−0.06–0.13)
No	Q1	146 044	17 705	Ref.
No	Q2	144 005	19 595	1.02 (0.99–1.05)
No	Q3	140 194	20 412	1.03 (0.99–1.07)
No	Q4	138 903	21 928	1.07 (1.02–1.13)
Yes	Q1	10 259	1779	1.49 (1.42–1.57)
Yes	Q2	9187	1820	1.55 (1.47–1.63)
Yes	Q3	8489	1849	1.62 (1.53–1.72)
Yes	Q4	8161	1837	1.60 (1.50–1.72)
3rd trimester					−0.03 (−0.12–0.06)
No	Q1	146 293	17 831	Ref.
No	Q2	145 118	19 782	1.00 (0.97–1.03)
No	Q3	139 473	19 962	0.98 (0.95–1.02)
No	Q4	138 104	21 901	1.03 (0.98–1.09)
Yes	Q1	10 268	1820	1.52 (1.45–1.60)
Yes	Q2	9262	1821	1.51 (1.43–1.59)
Yes	Q3	8356	1790	1.54 (1.47–1.64)
Yes	Q4	8218	1840	1.52 (1.42–1.63)
Entire pregnancy					−0.04 (−0.14–0.05)
No	Q1	142 313	16 929	Ref.
No	Q2	142 474	19 688	1.03 (1.00–1.06)
No	Q3	141 971	19 741	0.95 (0.91–1.00)
No	Q4	135 596	22 224	1.07 (1.00–1.13)
Yes	Q1	10 041	1768	1.55 (1.47–1.62)
Yes	Q2	9096	1788	1.54 (1.46–1.62)
Yes	Q3	8653	1808	1.50 (1.41–1.59)
Yes	Q4	7850	1831	1.58 (1.47–1.70)
First year of life					0.01 (−0.08–0.10)
No	Q1	141 974	16 918	Ref.
No	Q2	142 101	19 682	0.99 (0.96–1.02)
No	Q3	141 788	19 738	1.00 (0.95–1.05)
No	Q4	134 323	22 221	1.02 (0.98–1.07)
Yes	Q1	9874	1766	1.55 (1.46–1.61)
Yes	Q2	8921	1784	1.53 (1.41–1.60)
Yes	Q3	8365	1807	1.57 (1.45–1.64)
Yes	Q4	7538	1830	1.59 (1.46–1.69)

Data are presented as n, unless otherwise stated. Q: quartile; RERI: relative excess risk of childhood asthma due to interaction between maternal asthma and PM_2.5. ^#: models adjusted for maternal age at delivery, infant sex, parity, breastfeeding status at the time of discharge, maternal smoking during pregnancy, gestational age, birthweight, residential greenness exposure during pregnancy, dissemination area median family income, dissemination area proportion of population who are visible minority, dissemination area proportion of the adult female population aged 25–64 years who completed post-secondary education, the average pregnancy exposure to the selected pollutant, the first year of life exposure to the selected pollutant and cumulative exposure after birth to the selected pollutant.