. 2020 Jan 7;128(1):017006. doi: 10.1289/EHP5117

Table 3.

Relative excess risk due to interaction of heatwave and ${PM}_{2.5}$ exposure on preterm birth in Guangzhou, China, 2015–2017.

Heatwaves	Overall PTB^a		Overall PTB^b		PTB at weeks 28–34^b		PTB at weeks 35–36^b
Heatwaves	Unadjusted RERI	95% CI	Adjusted RERI	95% CI	RERI	95% CI	RERI	95% CI
33°C-D2	2.33	$- 0.46$ , 5.11	2.43	$- 0.45$ , 5.31	0.78	$- 0.57$ , 2.13	0.94	$- 0.71$ , 2.59
33°C-D3	1.70	$- 0.43$ , 3.82	1.66	$- 0.50$ , 3.83	1.30	$- 0.95$ , 3.55	0.59	$- 0.50$ , 1.69
33°C-D4	0.91	$- 1.36$ , 3.17	0.89	$- 1.73$ , 3.52	1.50	$- 0.37$ , 3.38	0.19	$- 1.71$ , 2.09
75th-D2	1.88	$- 1.83$ , 5.59	1.81	$- 2.18$ , 5.80	0.87	$- 0.14$ , 1.88	0.41	$- 2.35$ , 3.18
75th-D3	2.31	$- 2.59$ , 7.20	2.15	$- 2.89$ , 7.19	0.84	$- 0.20$ , 1.89	0.94	$- 2.90$ , 4.78
75th-D4	1.64	$- 2.37$ , 5.64	1.35	$- 2.76$ , 5.47	1.65	$- 0.41$ , 3.72	0.33	$- 2.81$ , 3.47
90th-D2	0.49	$- 3.88$ , 4.86	0.15	$- 4.53$ , 4.83	1.62	0.07, 3.17	$- 1.28$	$- 3.79$ , 1.24
90th-D3	$- 0.74$	$- 3.13$ , 1.66	$- 1.10$	$- 3.90$ , 1.71	2.64	$- 0.41$ , 5.69	$- 1.9$	$- 3.74$ , $- 0.05$
90th-D4	$- 1.67$	$- 4.30$ , 0.96	$- 1.89$	$- 5.28$ , 1.51	2.53	$- 2.15$ , 7.22	$- 1.66$	$- 4.73$ , 1.40
95th-D2	$- 0.64$	$- 2.98$ , 1.69	$- 1.07$	$- 3.89$ , 1.75	1.05	$- 0.15$ , 2.25	$- 2.24$	$- 4.11$ , $- 0.37$
95th-D3	$- 11.2$	$- 21.27$ , $- 1.14$	$- 14.4$	$- 27.46$ , $- 1.33$	9.62	$- 7.71$ , 26.95	$- 9.83$	$- 23.43$ , 3.77
98th-D2	$- 6.85$	$- 13.93$ , 0.23	$- 8.64$	$- 17.46$ , 0.19	10.99	$- 18.51$ , 40.50	$- 5.76$	$- 13.63$ , 2.10

Note: Heatwaves were defined by an absolute (33°C) or percentile temperature threshold (75th, 90th, 95th, 98th percentiles, corresponding to 34.6°C, 35.7°C, 36.4°C, and 37°C, respectively) and by the number of consecutive days above the threshold (2–4 d, indicated by D2, D3, or D4); ${PM}_{2.5}$ exposure in the last gestational week was included in each model as a continuous variable. Each RERI was calculated for per $10 {- μ g / m}^{3}$ increment in ${PM}_{2.5}$ with each heatwave exposure. CI, confidence interval; ${PM}_{2.5}$ , particulate matter $< 2.5 μ m$ in aerodynamic diameter; PTB, preterm birth; RERI, relative excess risk due to interaction.

Unadjusted model included only gestational temperature and ${PM}_{2.5}$ exposures; residency districts of the participants were fitted as a random effect.

Adjusted model additionally included maternal age, parity, month of birth, and relative humidity in the last gestational week before delivery.