Critique Table 2.

Overview of Main Analyses Using Logistic Regression^a

Aim	Description	Cohort or Case– Control	Dependent Variables (Dichotomous)	Exposure		Models/Other Covariates	Multipollutant Models?
				Metric	Exposure Assignment
1	Evaluate the effects of individual pollutants during vulnerable periods in pregnancy on adverse pregnancy outcomes	Cohort	PTB (<37 wks) LBW (<2500 g) IUGRb	Continuous variable: Daily mean PM2.5, PM10, SO2, NO2, CO, O3 Averaging times: full period of gestation, trimester, monthc	Nearest monitor: Maternal residence at time of child’s birth in community wholly or partially within 5 km (15 km for PM2.5) of a monitoring station	Model 1: Crude Model 2: Main model, adjusted for covariate data collected at deliveryd	Single-pollutant models
2	Same as Aim 1 but with two-pollutant models	Cohort	PTB LBW IUGR	Same as above	Same as above	Main model, adjusted for covariate data collected at deliveryd	Two-pollutant models
3	Evaluate how residual confounding affected the associations	Nested case– control	PTB LBW No IUGR in the case–control study	Dichotomous exposure variablese Averaging times: full period of gestation, trimester (appendix only), month (appendix only)c	Inverse distance weighted (IDW) between maternal address at time of child’s birth and 3 nearest monitors within 5 km	Model 1: Crude, no covariates Model 2: Adjusted for data at deliveryd Model 3: Adjusted for delivery data and questionnaire dataf Model 4: Two-phase models, corrected for nonresponses, adjusted for delivery data and questionnaire data	Single-pollutant models
4	Evaluate whether the associations are modified by extremes of temperature, SES, household income, or SHS exposure	Cohort	PTB LBW IUGR	Continuous variable: Daily mean PM2.5, PM10, SO2, NO2, CO, O3 Averaging times: full period of gestation, trimester, monthc	Nearest monitor: Maternal residence at time of child’s birth in community wholly or partially within 5 km (15 km for PM2.5) of a monitoring station	Stratify by temperature at conception, maternal education, household income, SHS exposure Adjust for covariate data collected at deliveryd	Single-pollutant models

^a Most of the analyses reported were conducted using logistic regression. Analyses using linear regression are shown in Appendix M (Tables M.50 through M.52) available on the HEI Web site, but the authors argued against their use in the text.

^b IUGR is defined as an infant whose birth weight falls below the 10th percentile of all singleton live births, between 2011 and 2013, in Wuhan who were in the same stratum by sex and week of gestation as the target infant.

^c Averaging periods for exposure included (1) the full period of gestation from conception to birth; (2) trimester; and (3) the first, second, third, next-to-last, and last months of pregnancy.

^d Delivery data included maternal age, maternal educational attainment, maternal occupation, gravidity, parity, infant sex, season of conception, and ambient temperature during the week of conception.

^e The cut points were values close to the pollutant medians and differed slightly by pollutant and outcome. For PM_2.5, they were 63.7 μg/m³ (PTB) and 65.8 μg/m³ (LBW); for PM₁₀, they were 99.5 μg/m³ (PTB) and 96.6 μg/m³ (LBW); for SO₂, they were 34.9 μg/m³ (both PTB and LBW); for NO₂, they were 58.8 μg/m³ (PTB) and 58.9 μg/m³ (LBW); for CO, they were 987.5 μg/m³ (PTB) and 1010.8 μg/m³ (LBW); and for O₃, they were 70.8 μg/m³ (PTB) and 72.3 μg/m³ (LBW).

^f Adjusted for covariates from the delivery data plus additional covariates from the survey including total household income, SHS exposure, maternal depression during pregnancy, and vaginal bleeding during pregnancy.