Characteristics of the study cohorts
| Characteristic | LHIN subregion; no. (%) of patients* | p value | ||
|---|---|---|---|---|
| Lambton n = 16 758 | Windsor n = 34 962 | London–Middlesex n = 62 707 | ||
| Maternal characteristics at delivery date | ||||
| Age, yr, mean ± SD | 27.94 ± 5.37 | 28.30 ± 5.47 | 29.11 ± 5.44 | < 0.001 |
| Age group, yr | ||||
| 15–29 | 10 203 (60.9) | 20 261 (58.0) | 31 930 (50.9) | < 0.001 |
| 30–39 | 6285 (37.5) | 14 029 (40.1) | 29 366 (46.8) | |
| 40–49 | 270 (1.6) | 672 (1.9) | 1411 (2.3) | |
| Rural geography | 4557 (27.2) | 15 (0.0) | 3264 (5.2) | < 0.001 |
| Income quintile | ||||
| 1 (lowest) | 3918 (23.4) | 10 971 (31.4) | 14 272 (22.8) | < 0.001 |
| 2 | 3408 (20.3) | 9105 (26.0) | 13 397 (21.4) | |
| 3 | 3394 (20.3) | 7551 (21.6) | 12 723 (20.3) | |
| 4 | 3406 (20.3) | 4083 (11.7) | 12 277 (19.6) | |
| 5 (highest) | 2509 (15.0) | 3200 (9.2) | 9887 (15.8) | |
| Missing | 123 (0.7) | 52 (0.1) | 151 (0.2) | |
| Residential instability | ||||
| 1 (least instability) | 2391 (14.3) | 2810 (8.0) | 9436 (15.0) | < 0.001 |
| 2 | 3483 (20.8) | 4783 (13.7) | 11 554 (18.4) | |
| 3 | 4533 (27.0) | 6985 (20.0) | 11 834 (18.9) | |
| 4 | 3681 (22.0) | 11 184 (32.0) | 13 382 (21.3) | |
| 5 (most instability) | 2670 (15.9) | 9200 (26.3) | 16 501 (26.3) | |
| Material deprivation | ||||
| 1 (least deprived) | 2541 (15.2) | 3993 (11.4) | 11 889 (19.0) | < 0.001 |
| 2 | 3319 (19.8) | 6411 (18.3) | 10 960 (17.5) | |
| 3 | 3400 (20.3) | 5455 (15.6) | 13 039 (20.8) | |
| 4 | 3114 (18.6) | 6975 (20.0) | 13 119 (20.9) | |
| 5 (most deprived) | 4384 (26.2) | 12 128 (34.7) | 13 700 (21.8) | |
| Dependency | ||||
| 1 (lowest | 1543 (9.2) | 5591 (16.0) | 15 393 (24.5) | < 0.001 |
| 2 | 2934 (17.5) | 7869 (22.5) | 16 275 (26.0) | |
| 3 | 3575 (21.3) | 7872 (22.5) | 14 897 (23.8) | |
| 4 | 4277 (25.5) | 8810 (25.2) | 9438 (15.1) | |
| 5 (highest | 4429 (26.4) | 4820 (13.8) | 6704 (10.7) | |
| Ethnic concentration | ||||
| 1 (lowest) | 6903 (41.2) | 3509 (10.0) | 9437 (15.0) | < 0.001 |
| 2 | 4688 (28.0) | 4400 (12.6) | 11 755 (18.7) | |
| 3 | 3435 (20.5) | 6268 (17.9) | 17 248 (27.5) | |
| 4 | 1553 (9.3) | 10 080 (28.8) | 15 731 (25.1) | |
| 5 (highest) | 179 (1.1) | 10 705 (30.6) | 8536 (13.6) | |
| Newborn characteristics | ||||
| Sex, female | 8224 (49.1) | 16 982 (48.6) | 30 543 (48.7) | 0.6 |
| Low birth weight or preterm† | 1445 (8.6) | 3104 (8.9) | 5533 (8.8) | 0.6 |
| Pollutant exposures in year of birth | ||||
| NO2,‡ ppb, mean ± SD | 28.4 ± 4.8 | 34.9 ± 3.9 | 28.5 ± 4.2 | < 0.001 |
| O3,‡ ppb, mean ± SD | 41.8 ± 1.9 | 39.6 ± 2.6 | 40.3 ± 2.0 | < 0.001 |
| PM2.5,‡ ppb, mean ± SD | 23.6 ± 2.8 | 21.3 ± 1.5 | 17.7 ± 1.6 | < 0.001 |
| SO2,‡ ppb, mean ± SD | 8.8 ± 1.8 | 6.6 ± 1.7 | 2.75 ± 0.9 | < 0.001 |
Note: LHIN = Local Health Integration Network, NO2 = nitrogen dioxide, O3 = ozone, PM2.5 = fine particulate matter, ppb = parts per billion, SD = standard deviation, SO2 = sulphur dioxide.
↵* Except where indicated otherwise.
↵† Low birth weight or preterm refers to infants born with low birth weight < 2500 g, small for gestational age, intrauterine growth restriction or preterm gestation < 37 weeks. All diagnostic codes are detailed in Appendix 1, Table S1.
↵‡ NO2 and O3 data were available for the period Jan. 1, 1996, to Mar. 31, 2009; PM2.5 data for the period Jan. 1, 2003, to Mar. 31, 2009; and SO2 data for the period Apr. 1, 1993, to Mar. 31, 2009 (full study period). Pollution values were based on annual summaries and were assigned to children at the time (i.e., year) of birth and location of birth (i.e., residential Forward Sortation Area [geographic unit based on postal code with 400–700 persons living there] or city region of birth, depending on the source of the data).