Study group

Control group

Risk factors of preterm birth

n = 60

n = 243

Odds ratio

CI (95%)

Low and middle school education status

88.3%

60.2%

5.01

2.19 - 11.49

Thyroid disease in last 12 months

23.3%

9.1%

3.06

1.46 - 6.42

Smoking at diagnosis of pregnancy

27.6%

13.5%

2.45

1.23 - 4.87

Diabetes in last 12 months

1.7%

0.4%

4.10

0.25 - 66.55

Hypertension in last 12 months

5.0%

3.3%

1.55

0.40 - 6.01

Hospital admission(s) in last 12 months

21.7%

17.7%

1.29

0.64 - 2.58

Body mass index (≥25, <25)

28.3%

25.5%

1.15

0.61 - 2.17

Gynecological surgery ever

44.0%

41.2%

1.12

0.60 - 2.09

Former preterm birth

13.3%

12.4%

1.08

0.47 - 2.50

Self-assessed health status

25.0%

24.5%

1.03

0.53 - 1.98

Psychological Stress

32.1%

33.6%

0.94

0.50 - 1.75

Vaginal infection(s) in last 12 months

11.1%

12.5%

0.88

0.09 - 8.56

Former miscarriage(s)

25.0%

32.1%

0.71

0.37 - 1.34

Further complications in former pregnancies

40.0%

50.4%

0.66

0.37 - 1.16

Age ≥ 30 years/<30 years

71.7%

81.5%

0.57

0.30 - 1.10

Former induced abortion

6.7%

11.1%

0.57

0.19 - 1.70

Fertility treatment

8.3%

27.7%

0.24

0.09 - 0.62