Preterm birth and PM2.5 in Puerto Rico: evidence from the PROTECT birth cohort

Table 3 Risk ratios and 95% CIs of preterm birth for an interquartile range increase in prenatal PM_2.5 exposure among participants in the PROTECT cohort in Puerto Rico, stratified by mother’s characteristics^a

Characteristic	Number of births (Number of PTBs)	Risk ratio (95% CI)	p-value
Age of mother (years)			0.28
< 25	539 (46)	1.01 (0.98, 1.03)
≥ 25	553 (53)	1.01 (1.00, 1.02)
Annual family income, US dollars			0.36
< 30,000	573 (62)	1.01 (0.99, 1.03)
≥ 30,000	362 (26)	1.00 (0.99, 1.01)
Infant sex			0.12
Male	572 (59)	1.00 (0.98, 1.02)
Female	519 (40)	1.02 (1.00, 1.04)
History of adverse pregnancy outcomes			0.72
No	833 (68)	1.00 (0.98, 1.03)
Yes	259 (31)	1.01 (1.00, 1.02)
Pre-pregnancy body mass index			0.74
Not obese	853 (68)	1.01 (1.00, 1.02)
Obese	179 (21)	1.00 (0.97, 1.03)
Number of pregnancies			0.98
Only this one	454 (39)	1.01 (0.99, 1.02)
Have had other pregnancies	624 (59)	1.01 (0.99, 1.02)
Education level			0.30
≤ High school	351 (47)	1.01 (0.98, 1.04)
> High school	724 (51)	1.00 (0.99, 1.02)
Prenatal DBP			0.50
Median (2.70) or less	354 (25)	0.83 (0.62, 1.10)
More than median	352 (33)	0.97 (0.77, 1.24)
Prenatal DiBP			0.63
Median (2.68) or less	355 (22)	0.94 (0.77, 1.15)
More than median	351 (36)	0.97 (0.67, 1.39)

DBP di-n-butyl phthalate, DiBP di-isobutyl phthalate
^a All estimates are from fully adjusted models, with adjustment for individual-level covariates (mother’s age, number of other children [alive or deceased], infant’s sex, gestational age, season of birth, education level, urban/rural residence, marital status, number of prenatal visits attended, and year of birth) and area/municipality-level covariates (including population density, income per capita, proportion of non-white non-Hispanic residents, average unemployment rate, proportion of occupied housing units with at least one of four severe US Department of Housing and Urban Development-designated defects, percentage of residents with a less than high school level of education, and the age adjusted prevalence of diabetes mellitus)

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