Table 2.

Associations of extreme climate events with preterm birth, stratified by clinical subtypes in China Labor and Delivery Survey ($n=\mathrm{70,818}$).

Variables	Spontaneous PTB [OR (95% CI)]	PPROM [OR (95% CI)]	Iatrogenic PTB [OR (95% CI)]
1 wk before delivery	$n=\mathrm{2,454}$	$n=\mathrm{1,358}$	$n=\mathrm{1,153}$
5th-days	1.07 (1.03, 1.12)	1.10 (1.04, 1.16)	1.02 (0.95, 1.08)
5th-2D	1.13 (0.95, 1.35)	1.40 (1.12, 1.75)	1.04 (0.80, 1.36)
10th-days	1.06 (1.03, 1.10)	1.10 (1.05, 1.15)	1.02 (0.96, 1.07)
10th-3D	1.15 (1.06, 1.24)	1.10 (0.98, 1.23)	0.94 (0.82, 1.08)
10th-2D	1.13 (1.05, 1.22)	1.16 (1.05, 1.29)	1.06 (0.94, 1.19)
90th-days	0.99 (0.95, 1.03)	0.92 (0.87, 0.96)	0.96 (0.91, 1.01)
90th-3D	0.94 (0.87, 1.02)	0.86 (0.77, 0.96)	0.94 (0.84, 1.05)
90th-2D	1.00 (0.92, 1.08)	0.90 (0.81, 1.01)	0.98 (0.87, 1.10)
95th-days	1.00 (0.95, 1.04)	0.97 (0.91, 1.03)	0.96 (0.90, 1.03)
95th-2D	1.16 (1.06, 1.26)	1.07 (0.95, 1.20)	0.94 (0.83, 1.08)
2 wk before delivery	$n=\mathrm{2,454}$	$n=\mathrm{1,358}$	$n=\mathrm{1,153}$
5th-days	1.04 (1.01, 1.06)	1.05 (1.02, 1.08)	1.00 (0.97, 1.04)
5th-2D	1.08 (1.02, 1.13)	1.09 (1.02, 1.17)	1.02 (0.94, 1.11)
10th-days	1.03 (1.01, 1.05)	1.05 (1.02, 1.08)	1.00 (0.97, 1.03)
10th-3D	1.09 (1.02, 1.16)	1.17 (1.07, 1.28)	0.99 (0.89, 1.10)
10th-2D	1.06 (1.02, 1.10)	1.09 (1.03, 1.15)	1.01 (0.95, 1.08)
90th-days	1.00 (0.98, 1.03)	0.96 (0.93, 0.98)	0.99 (0.96, 1.03)
90th-3D	1.02 (0.95, 1.10)	0.88 (0.80, 0.98)	1.02 (0.92, 1.12)
90th-2D	1.01 (0.96, 1.05)	0.93 (0.87, 0.99)	0.99 (0.92, 1.05)
95th-days	1.01 (0.99, 1.04)	0.97 (0.93, 1.01)	0.98 (0.94, 1.03)
95th-2D	1.03 (0.96, 1.09)	0.94 (0.86, 1.03)	0.95 (0.86, 1.04)

Note: Generalized linear mixed models were used to examine the associations. All models were adjusted for maternal age, maternal ethnicity, maternal education, insurance type, child sex, parity, GDP per capita, geographic region, conception season, conception year, ${\mathrm{PM}}_{2.5}$, and ${\mathrm{O}}_3$. Fifth-days, 10th-days, 95th-days, and 90th-days represent the total number of days when the daily mean temperature was lower than the 5th or the 10th percentile or higher than the 95th or the 90th percentile, respectively. Fifth-2D, 10th-3D, 10th-2D, 95th-2D, 90th-3D and 90th-2D represent the total number of extreme weather events. An extreme weather event can be defined as the daily mean temperature below the fifth percentile or higher than the 95th percentile for 2 consecutive days or the daily mean temperature below the 10th percentile or higher than the 90th percentile for 2 or 3 consecutive days. GDP, gross domestic product; ${\mathrm{PM}}_{2.5}$, particulate matter with aerodynamic diameter $\le 2.5\mathrm{\mu }\mathrm{m}$; PPROM, preterm premature rupture of the fetal membranes; PTB, preterm birth.