Table 2.

Association between prenatal exposure to air pollution and childhood obesity in human epidemiologic studies

Study		Country	Study design	Study population			Obesity parameter	Air pollutant	Direction of relationship with obesity (+/-/0)	Findings
				Sample size (n)	Age at exposure (yr)	Age at outcome (yr)
Traffic density/proximity
	Fleisch et al. [14] 2015	USA	Cohort	2,115	3rd trimester	0–0.5	Weight-for-length	Traffic density	(+)	Negative association with fetal growth, but a positive association with obesity at the age of 6 mo
	Fleisch et al. [13] 2017	USA	Cohort	1,418	At delivery	3.3	BMI, skinfold thickness, WC, fat mass	Roadway proximity	(+)	Positive association with fat mass at early & mid-childhood
						7.7
	Fleisch et al. [12] 2019	USA	Cohort	1,649	3rd trimester	0.5–10	BMI	Traffic density	(+)	Positive association with obesity at the age of 0.5–10
NOx/SO2/elemental carbon
	Frondelius et al. [15] 2018	Sweden	Cohort	5,815	Entire pregnancy	4	BMI	NOx	0	No association with overweight/obesity at the age of 4
	Kim et al. [16] 2018	USA	Cohort	2,318	Entire pregnancy	10	BMI	NOx	0	No association with attained BMI at the age of 10
	Huang et al. [17] 2019	Hong Kong	Cohort	8,298	Entire pregnancy	9–15	BMI	NOx	0	No association with BMI at the age of 9–15
								SO2	(-)	Negative association with BMI at the age of 12–15 (only in boys)
	Sears et al. [49] 2019	USA	Cohort	657	Entire pregnancy	7–8	BMI	Elemental carbon	0	No association with BMI at the age of 7–8
PM
	Fleisch et al. [14] 2015	USA	Cohort	2,115	3rd trimester	0–0.5	Weight-for-length	PM2.5	0	No association with obesity at the age of 6 mo
	Fleisch et al. [13] 2017	USA	Cohort	1,418	3rd trimester	3.3	BMI, Skinfold thickness, WC, fat mass	PM2.5	(-)	Negative association with BMI and fat mass at early & mid-childhood
						7.7
	Chiu et al. [19] 2017	USA	Cohort	239	10–29 weeks gestation	4	WHR BMI, skinfold thickness, fat mass	PM2.5	(+)	Positive association with WHR at the age of 4 (only in girls)
										No association with other adiposity measures
	Mao et al. [18] 2017	USA	Cohort	1,446	Entire pregnancy	2–9	BMI	PM2.5	(+)	Positive association with childhood overweight or obesity
	Kim et al. [16] 2018	USA	Cohort	2,318	Entire pregnancy	10	BMI	PM2.5	0	No association with attained BMI at the age of 10
	Fleisch et al. [12] 2019	USA	Cohort	1,649	3rd trimester	0.5–10	BMI	PM2.5	0	No association between prenatal PM2.5 exposure and BMI outcomes at any age
	Huang et al. [17] 2019	Hong Kong	Cohort	8,298	Entire pregnancy	9–15	BMI	PM10	0	No association with BMI at the age of 9-15
Smoking
	Hawkins et al. [20] 2009	UK	Cohort	13,188	3-Month gestation	3	BMI	Smoking	(+)	Positive association with overweight at the age of 3
	Dancause et al. [22] 2012	Canada	Cohort	111	Preconception, entire pregnancy	5.5	BMI	Smoking	(0)	No association with obesity at the age of 5.5
	Wen et al. [21] 2013	USA	Cohort	21,063	3rd trimester	7	BMI, body weight	Smoking	(+)	Positive association with overweight at the age of 7
PAH
	Rundle et al. [23] 2012	USA	Cohort	702	3rd trimester	7	BMI, fat mass	PAHs	(+)	Positive association with obesity at the age of 7
	Rundle et al. [50] 2019	USA	Cohort	535	3rd trimester	5-14	BMI	PAHs	(+)	Positive association with childhood BMI at the age of 5–10

Direction of relationship with obesity: (+), factor related to greater childhood obesity; (-), factor related to decreased childhood obesity; (0), no relationship with childhood obesity

BMI, body mass index; NOx, nitrogen oxides; PAHs, polycyclic aromatic hydrocarbons; PM_2.5, particulate matter <2.5 microns in diameter; PM₁₀, particulate matter <10 microns in diameter; SO₂, sulfur dioxide; WC, waist circumference; WHR, waist-to-hip ratio.