Table 2.

Clinically identifiable risk factors for spontaneous preterm birth

	Sensitivity (%)	PPV (%)	False positive rate (%)	Relative risk or odds ratio
Short cervix	35–40
(<35 weeks)8,10,11	34		5
(<32 weeks)52	48 (55)		5 (10)
Short cervix + vaginal bleeding				4.6 (2.7–8.0)65
Prior sPTB				2.0 (1.6–2.5)66
Fetal loss < 16 weeks				1.48
Fetal loss 16–24 weeks				1.779
sPTB 24–32 weeks				5.498
Short cervix + vaginal bleeding + Prior sPTB				4.84 (1.89–12.4)65
Risk scoring system (<37 weeks)67	38		17
Multiparous; Nulliparous66	24.2; 18.2	28.6; 33.3
Maternal factors (Age + Ob Hx) (<32 weeks)52	29 (38)		5 (10)
Maternal factors + cervix length (<32 weeks)52	57 (69)		5 (10)
FFN+ (<34 weeks)68	61 (33–89)	9–46
Vaginal bleeding				1.3 (1.1–1.6)69
(1st or 2nd trimester)				1.58 (1.27–1.96)65 1.6 (1.1–2.3)66
Bacterial vaginosis		6–49		1.5–3-fold70
Smoking				1.488
Illicit drug use/heavy alcohol use				1.08
Maternal age < 20 years				1.428
>35 years				1.1
Ethnicity – Black				1.89 (1.1–3.27)66 1.668
Prior cervical surgery				1.08
Body mass index < 19.8				2.3 (1.37–3.92)66
>32.2 ± 2.2 kg/m2 (<34 weeks)				2.23 (1.19–4.18)71
Clinical depression				<2-fold70
Socioeconomic status				2.0 (1.19–3.44)66
Single marital status				1.4–1.866
Long work hours/hard physical labor; stress				<2-fold70
Interpregnancy interval < 6 months				2.272
Multiple gestation	(60)70
Polyhydramnios/oligohydramnios				1.8 (1.03–3.15)73
Maternal medical and surgical disorders				0.7–1.3466
Uterine anomalies				5.9 (4.3–8.1)74
Intrauterine; vaginal or maternal systemic infections				Twofold70
Periodontal disease				2.83 (1.95–4.1)75
No risk factors (>50% of all PTBs)29

Abbreviations: FFN, fetal fibronectin; Ob Hx, obstetrical history; sPTB, spontaneous preterm births.