Table 1 Characteristics of the study population

Age (years)^a

31.8 ± 3.9

Maternal BMI (kg/m²)^a

24.55 ± 4.76

Nulliparity (%)

47 (55.2)

Cesarean section (%)

41 (48.2)

Gestational age at inclusion (weeks)^a

29.4 ± 3.6

Cervical length at inclusion (mm)^b

22.9 (0–45)

Cervical length < 25th percentile (%)

44 (51.8)

Positive fFN finding (%)

31 (36.5)

Tocolytics use (%)

58 (68.2)

ACS (%)

56 (65.9)

Gestational age at delivery (weeks)^a

35.7 ± 3.7

Inclusion to delivery interval (days)^b

45.0 (0–121)

Preterm birth at < 34 weeks (%)

20 (23.5)

Preterm birth at < 37 weeks (%)

42 (49.4)

Delivery within 7 days (%)

15 (17.6)

Delivery within 14 days (%)

17 (20.0)