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Table 1 Demographic information and other characteristics of Mothers in cases and control groups (categorical variables)

From: Assessing the risk factors before pregnancy of preterm births in Iran: a population-based case-control study

Items Preterm delivery Total
N (%)
Control
N (%)
Case
N (%)
All participants 1795 (73.0) 668 (27.0)  
Age(years)
 < 35 1674 (94.0) 588 (88.8) 2262 (92.6)
 ≥ 35 107 (6.0) 74 (11.2) 181 (7.4)
Level of Education
 Illiterate 76 (4.2) 39 (5.9) 115 (4.7)
 Primary 366 (20.4) 172 (25.8) 538 (21.9)
 Guidance 449 (25.0) 126 (18.9) 575 (23.4)
 High school 689 (38.4) 251 (37.7) 940 (38.2)
 Collegiate 213 (11.9) 78 (11.7) 291 (11.8)
Ethnic
 Tork 366 (21.7) 38 (6.1) 404 (17.5)
 Lor 73 (4.3) 37 (5.9) 110 (4.8)
 Fars 1083 (64.1) 479 (76.8) 1562 (67.5)
 Kord 29 (1.7) 23 (3.7) 52 (2.2)
 Arab 20 (1.2) 6 (1.0) 26 (1.1)
 Balooch 11 (0.7) 6 (1.0) 17 (0.7)
 Torkaman 99 (5.9) 32 (5.1) 131 (5.7)
 Else 9 (0.5) 3 (0.5) 12 (0.5)
Occupation
 Housewife 1610 (90.9) 610 (91.9) 2220 (91.2)
 Employee 110 (6.2) 40 (6.0) 150 (6.2)
 Farmer& carpet weaver 31 (1.8) 7 (1.1) 38 (1.6)
 Other 20 (1.1) 7 (1.1) 27 (1.1)
Place of Residence
 Urban 694 (39.7) 314 (48.1) 1008 (42.0)
 Rural 1053 (60.3) 339 (51.9) 1392 (58.0)
Abortion history
 Yes 154 (8.6) 102 (15.3) 256 (10.4)
 No 1641 (91.4) 566 (84.7) 2207 (89.6)
Stillbirth history
 Yes 104 (5.8) 122 (18.3) 226 (9.2)
 No 1691 (94.2) 546 (81.7) 2237 (90.8)
Cesarean history
 Yes 205 (11.4) 86 (12.9) 291 (11.8)
 No 1590 (88.6) 582 (87.1) 2172 (88.2)
Gap pregnancy(years)
 Upper than 3 537 (30.4) 189 (28.9) 726 (30.0)
 Lower than 1 74 (4.2) 55 (8.4) 129 (5.3)
 1–3 496 (28.1) 153 (23.4) 649 (26.8)
 Primary pregnancy 661 (37.4) 257 (39.3) 918 (37.9)
Consanguineous marriage
 Yes 494 (28.1) 205 (31.3) 699 (29.0)
 No 1263 (71.9) 450 (68.7) 1713 (71.0)
Supplements Consumption
 Yes, use regular 1449 (81.8) 535 (80.5) 1984 (81.4)
 Yes, use not regular 213 (12.0) 91 (13.7) 304 (12.5)
 Use not 109 (6.2) 39 (5.9) 148 (6.1)
BMI
 Normal 893 (53.6) 292 (48.7) 1185 (52.3)
 Underweight 313 (18.8) 126 (21.0) 439 (19.4)
 Overweight 329 (19.7) 121 (20.2) 450 (19.9)
 Obesity grade1 101 (6.1) 55 (9.2) 156 (6.9)
 Obesity grade 2 31 (1.9) 5 (0.8) 36 (1.6)
Regular Cycles of period
 Yes 1564 (90.2) 536 (82.7) 2100 (88.2)
 No 170 (9.8) 112 (17.3) 282 (11.8)