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Table 1 Preterm and term births by maternal and infant characteristics, city, season and year

From: Air pollution in the week prior to delivery and preterm birth in 24 Canadian cities: a time to event analysis

Variable Number of Birthsa Percent Preterm
Preterm Term Total
Maternal age (years)
 19 or less 3515 38,690 42,200 8.33
 20–29 33,795 501,050 534,845 6.32
 30–39 39,760 587,780 627,540 6.34
 40+ 3800 39,765 43,565 8.72
 Missing 10 75 90 11.11
Maternal marital status     
 Single 18,080 223,090 241,170 7.50
 Married 51,410 809,340 860,755 5.97
 Widowed 70 965 1035 6.76
 Divorced 1050 12,175 13,225 7.94
 Separated 330 3345 3675 8.98
 Missing 9935 118,450 128,385 7.74
Parity     
 0 41,025 546,435 587,460 6.98
 1 23,890 405,325 429,215 5.57
 2 15,775 213,305 229,080 6.89
 Missing 190 2300 2490 7.63
Maternal country of birth     
 Other 33,855 500,350 534,205 6.34
 Canada 45,085 642,225 687,310 6.56
 Missing 1935 24,790 26,725 7.24
Infant sex     
 Male 44,380 596,410 640,790 6.93
 Female 36,495 570,950 607,445 6.01
 Missing 5 5 10 50.00
City     
 St. John’s 725 8570 9295 7.80
 Saint John 455 6760 7215 6.31
 Fredericton 335 4620 4955 6.76
 Quebec 2630 37,975 40,605 6.48
 Trois Rivieres 625 9690 10,315 6.06
 Montreal 11,350 170,830 182,180 6.23
 Ottawa 5110 76,605 81,715 6.25
 Oshawa 855 12,845 13,700 6.24
 Toronto 17,395 265,895 283,290 6.14
 Mississauga 4340 72,490 76,830 5.65
 Brampton 3695 52,325 56,020 6.60
 Hamilton 3205 44,960 48,165 6.65
 St. Catharines 690 11,390 12,085 5.71
 Kitchener 1370 21,600 22,970 5.96
 Windsor 1445 21,885 23,330 6.19
 Winnipeg 4965 64,845 69,810 7.11
 Calgary 8980 111,425 120,405 7.46
 Edmonton 6630 78,655 85,285 7.77
 Richmond 835 14,630 15,470 5.40
 Vancouver 3475 51,610 55,085 6.31
 Victoria 375 5805 6180 6.07
 Nanaimo 425 6385 6810 6.24
 Kamloops 440 6940 7385 5.96
 Kelowna 525 8620 9150 5.74
Birth year     
 1999 7660 113,210 120,875 6.34
 2000 7980 113,205 121,185 6.58
 2001 7810 115,315 123,130 6.34
 2002 7750 113,460 121,210 6.39
 2003 6880 100,615 107,495 6.40
 2004 8115 115,690 123,805 6.55
 2005 8365 118,735 127,100 6.58
 2006 8505 122,110 130,615 6.51
 2007 8720 125,625 134,340 6.49
 2008 9090 129,395 138,485 6.56
Season     
 Spring (Apr-Jun) 20,725 300,785 321,510 6.45
 Summer (Jul-Sep) 20,195 305,135 325,330 6.21
 Autumn (Oct-Dec) 19,850 280,030 299,880 6.62
 Winter (Jan-Mar) 20,110 281,415 301,525 6.67
Gestation (weeks)     
 20–27 4590 0 4590 .
 28–31 6580 0 6580 .
 32–33 8735 0 8735 .
 34–36 60,970 0 60,970 .
 37+ 0 1,167,365 1,167,365 .
Total 80,875 1,167,365 1,248,240 6.48
Total (excluding missing covariates) 63,400 938,300 1,001,700 6.34
  1. aIn accordance with Statistics Canada disclosure rules, case counts of less than five were suppressed, and all frequencies were randomly rounded to base five. As a result, there may be discrepancies between column totals and totals by infant/maternal characteristic. Statistical analyses employed unrounded data