Air pollutant exposure and outcome definitions of studies included
| Source | Outcome | Definition of outcome | Exposure | Definition of exposure | Exposure estimates |
| Choe et al12 | GDM | Birth certificate data and ICD-9648.8x were listed, and absent otherwise. | PM2.5, black carbon | PM2.5 and black carbon from spatiotemporal models. | Mean±SD First trimester PM2.5: 9.7±1.9 µg/m3; second trimester PM2.5: 9.6±1.9 µg/m3 Third trimester PM2.5: 9.5±2.1 µg/m3; first trimester black carbon: 0.5±0.1 µg/m3; second trimester black carbon: 0.5±0.1 µg/m3; third trimester black carbon: 0.5±0.1 µg/m3 |
| Fleisch et al13 | GDM | Failed GCT(1) with ≥2 high values on the OGTT(2). | PM2.5, black carbon, traffic exposure | PM2.5 and black carbon from central sites within 40 km of residence. PM2.5 and black carbon from spatiotemporal models. Neighborhood traffic density [(vehicles/day) × km] within 100 m. | Mean±SD From central sites: PM2.5: 10.9±1.4 µg/m3; black carbon: 0.9±0.1 µg/m3 From spatiotemporal models: PM2.5: 11.9±1.4 µg/m3; black carbon: 0.7±0.2 µg/m3 Traffic density: 1621±2234 (vehicles/day × km) |
| Fleisch et al14 | GDM | Failed GCT with ≥2 high values on the OGTT. | PM2.5, traffic exposure | PM2.5 from spatiotemporal models. Neighborhood traffic density [(vehicles/day) × km] within 100 m. | Mean±SD First trimester PM2.5: 10.4±1.7 µg/m3; second trimester PM2.5: 10.4±1.7 µg/m3 Traffic density: 1317±2025 (vehicles/day × km) |
| Hu et al15 | GDM | According to the American Diabetes Association 2003, failed GCT with ≥2 high values on the OGTT. | PM2.5, O3 | Air pollution exposure data were obtained from the US EPA and CDC’s National Environmental Public Health Tracking Network (2003–2005) (US EPA 2014) | Mean±SD Trimester 1 PM2.5: 9.73±2.07 µg/m3; O3: 37.20±6.04 ppb Trimester 2 PM2.5: 9.88±2.06 µg/m3; O3: 37.54±6.10 ppb Full pregnancy PM2.5: 9.93±1.67 µg/m3; O3: 37.40±4.10 ppb |
| Lu et al16 | GDM | A woman with a positive GCT and two or more abnormal 100 g OGTT values. | PM2.5, SO2, NOx, CO, O3 | The exposure assessment of this study based on data from a single fixed-site monitoring station (Chiayi station). | Mean±SD 3 months pre-pregnancy PM2.5: 44.38±12.09 µg/m3 First trimester PM2.5: 43.52±12.87 µg/m3; second trimester PM2.5: 41.20±13.43 µg/m3 |
| Malmqvist et al17 | GDM | GDM as defined in the Swedish Medical Birth Registry. | NOx, traffic exposure | Monthly and trimester means of NOx assigned by dispersion modeling at a spatial resolution of 500×500 m throughout the pregnancy. Traffic density within a 200 m radius. | Quartiles of NOx exposure (μg/m3): Q1: 2.5–8.9; Q2: 9.0–14.1; Q3: 14.2–22.6; Q4: >22.7 Categories of traffic density within 200 m (vehicles/min): 1: no road; 2: ＜2; 3: 2–5; 4: 5–10; 5: ＞10 |
| Pan et al18 | GDM | According to the American Diabetes Association criteria, had two of the abnormal values on the OGTT. | PM10, CO, NOx, SO2, O3 | Collected from 77 fixed-site air monitoring stations in Taiwan during 2004–2006. | Mean±SD PM10 (μg/m3): first trimester: 61.4±18.3; second trimester: 61.2±17.2; third trimester: 62.2±19.5 CO (ppm): first trimester: 0.6±0.1; second trimester: 0.6±0.1; third trimester: 0.6±0.2 NO (ppb): first trimester: 6.5±3.3; second trimester: 6.9±3.1; third trimester: 6.9±3.2 NO2 (ppb): First trimester: 20.2±5.3; second trimester: 19.8±5.5; third trimester: 19.1±5.9 NOx (ppb): first trimester: 26.6±7.8; second trimester: 26.5±7.8; third trimester: 25.7±8.2 SO2 (ppb): first trimester: 4.5±1.8; second trimester: 4.8±1.7; third trimester: 4.9±1.7 O3 (ppb): first trimester: 25.8±3.8; second trimester: 25.6±3.2; third trimester: 25.5±3.7 |
| Pedersen et al19 | GDM | Self-reported, physician-diagnosed GDM. | NO2, noise from road traffic (Lden) exposure | NO2 was using the advanced AirGIS dispersion model. Road traffic noise was using SoundPLAN based on the Nordic prediction method. | First trimester：NO2 (μg/m3): 11.5 (5.8, 27.4); road traffic noise (dB): 57.5 (49.3, 69.8); railway noise (dB): 51.3 (31.1, 68.6) |
| Robledo et al20 | GDM | GDM was recorded in the medical record or discharge records (code 648.8) using the International Classification of Diseases, Ninth Revision. | PM10, PM2.5, SO2, O3, CO, NOx | Using a modified Community Multiscale Air Quality (CMAQ) model version 4.7.1. | IQR Preconception PM2.5 (μg/m3): 5.54; PM10 (μg/m3): 6.3; SO2 (ppb): 3.30; NOx (ppb): 28.55; O3 (ppb): 12.33; CO (ppm): 0.26 First trimester PM2.5(μg/m3): 5.28; PM10 (μg/m3): 6.32; SO2 (ppb): 3.31; NOx (ppb): 30.21; O3 (ppb): 12.36; CO(ppm): 0.26 |
| Shen et al21 | GDM | International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code: 648.0 or 648.8. | PM10, PM2.5, SO2, O3, CO, NO2 | Collected from 76 fixed-site air quality monitoring stations supervised by the Taiwan Environmental Protection Agency during 2005–2013. | |
| van den Hooven et al 22 | GDM | GDM diagnosed according to the Dutch midwifery and obstetric guidelines. | Traffic exposure | Distance-weighted traffic density (DWTD) within a 150 m radius around residence (vehicles/24 hours × m); proximity to a major road (>10 000 vehicles/day). | Median (P25–P75) DWTD (vehicles/24 hours × m): 5.5×105 (1.6×105−1.2×106) Proximity to a major road (m): 140 (74–225) |
| Choe et al23 | GDM | ICD-9-CM code: 648.8. | PM2.5, NO2 | Air pollution samples were collected at 150 monitoring sites in each of the four seasons for one 2-week session and in every 2 weeks at five reference locations to track city-wide temporal variation. | Mean±SD Trimester 1 PM2.5: 12.0±2.5 µg/m3; NO2: 27.9±6.3 ppb Trimester 2 PM2.5: 11.9±2.4 µg/m3; O3: 27.9±6.3 ppb |
| Jo et al24 | GDM | Based on laboratory values confirming a plasma glucose level of 200 mg/dL or higher on the glucose challenge test or at least two plasma glucose values meeting or exceeding the following values on the 100 or 75 g oral glucose tolerance test. | PM2.5, PM10, NO2, O3 | Distance-weighted monthly average from four closest monitoring stations within 50 km, except for geocoded locations within 0.25 km of a monitor. | Mean±SD PM2.5: 18.2±5.5 µg/m3; PM10: 38.4±10.9 µg/m3; NO2: 25.8±8.2 ppb; O3: 41.3±7.6 ppb |
(1) Glucose change test: serum glucose 1 hour after a non-fasting 50 g oral glucose load. (2) Oral glucose tolerance test: serum glucose 3 hours after a fasting 100 g glucose load.
CDC, Centers for Disease Control and Prevention; CO, carbon monoxide; EPA, Environmental Protection Agency; GCT, glucose change test; GDM, gestational diabetes mellitus; NO, nitric oxide; NO2, nitrogen dioxide; NOx, nitrogen oxide; O3, ozone; OGTT, oral glucose tolerance test; PM10, particulate matter ≤10 μm in diameter; PM2.5, particulate matter ≤2.5 μm in diameter; SO2, sulfur dioxide.