Table 4  Risk factors for preterm birth.

Risk factor	OR	95% CI
3 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13
s/p spontaneous preterm birth	3.6	3.2 – 4.0
s/p medically indicated preterm birth	1.6	1.3 – 2.1
s/p conization	1.7	1.24 – 2.35
Interval between pregnancies is < 12 months	4.2	3.0 – 6.0
Pregnant woman is younger < 18 years	1.7	1.02 – 3.08
Poor socioeconomic living conditions	1.75	1.65 – 1.86
Single mother	1.61	1.26 – 2.07
Bacterial vaginosis	1.4	1.1 – 1.8
Asymptomatic bacteriuria	1.5	1.2 – 1.9
Vaginal bleeding in early pregnancy	2.0	1.7 – 2.3
Vaginal bleeding in late pregnancy	5.9	5.1 – 6.9
Twin pregnancy	ca. 6
Smoking	1.7	1.3 – 2.2
Periodontitis	2.0	1.2 – 3.2
Anemia	1.5	1.1 – 2.2