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Table 1 Characteristics of confounding factors for preterm birth (PTB) cases

From: Fermented foods and preterm birth risk from a prospective large cohort study: the Japan Environment and Children’s study

 

Preterm delivery

Non preterm delivery

p value

(n = 2343)

(n = 75,324)

Age, n (%)

< 0.001

 < 30 years old

867

(37.0)

29,388

(39.0)

 30–34 years old

796

(34.0)

26,841

(35.6)

 ≥ 35 years old

680

(29.0)

19,092

(25.4)

BMI(kg/m2) group, n (%)

< 0.001

 Leptosome (< 18.5)

488

(20.8)

12,272

(16.3)

 Healthy weight(18.5 to < 25)

1614

(68.9)

56,093

(74.5)

 Obese (≥ 25)

240

(10.3)

6924

(9.2)

Smoking history, n (%)

0.083

 Yes

999

(43.1)

30,862

(41.3)

 No

1321

(56.9)

43,931

(58.7)

Nulliparity, n (%)

0.022

 Yes

1015

(43.6)

30,927

(41.2)

 No

1314

(56.4)

44,135

(58.8)

Educational background (years), n (%)

0.028

 < 10

132

(5.9)

3410

(4.6)

 10–12

748

(33.4)

24,652

(33.2)

 13–15

883

(39.4)

29,886

(40.2)

 ≥ 16

476

(21.3)

16,417

(22.1)

Household income (million Japanese Yen/year), n (%)

0.032

 < 2

139

(6.6)

3769

(5.4)

 2 to < 4

706

(33.7)

24,147

(34.8)

 4 to < 6

728

(34.7)

22,976

(33.1)

 6 to < 8

303

(14.5)

11,068

(15.9)

 8 to < 10

125

(6.0)

4577

(6.6)

 ≥ 10

95

(4.4)

2947

(4.2)

Working > 42 h/week, n (%)

0.691

 Yes

481

(20.5)

15,211

(20.2)

 No

1862

(79.5)

60,113

(79.8)

Part-timer, n (%)

0.863

 Yes

371

(15.8)

12,027

(16.0)

 No

1972

(84.2)

63,297

(84.0)

  1. Note: BMI; body mass index before pregnancy