Acute Impact of Hourly Ambient Air Pollution on Preterm Birth

http://dx.doi.org/10.1289/EHP200



Table 1. Characteristics of mothers and preterm births in Brisbane, Australia, 2009–2013.
Variables n (%)
Total 6949 (100.0)
Maternal age (years)
< 35 5260 (75.7)
≥ 35 1689 (24.3)
Prepregnancy medical conditions
No 5122 (73.7)
Yes 1827 (26.3)
Previous pregnancy
0 2514 (36.2)
≥ 1 4435 (63.8)
Maternal smoking status
Smokers 773 (11.1)
Nonsmokers 6176 (88.9)
Number of births
Single 4929 (70.9)
Multiple 2020 (29.1)
Infant sex
Female 3276 (47.1)
Male 3673 (52.9)
SES index
Index 1–5 (low level) 910 (13.1)
Index 6–10 (high level) 6039 (86.9)