Table 1 Demographic characteristics of the term and preterm birth groups

Age, years, mean ± SD

33.1±4.2

32.2±3.5

0.164

BMI, kg/\(\hbox {m}^{2}\), mean ± SD

22.9±3.8

23.6±3.7

0.286

Gravidity, median (IQR)

2 (1-2)

2 (1-2)

0.431

Parity, median (IQR)

1 (0-1)

1 (0-1)

0.861

Gestation of previous spontaneous pregnancy loss\(^{a}\)

0.953

\(16^{+0}\)–\(19^{+6}\) weeks

28 (28.3)

16 (30.2)

\(20^{+0}\)–\(27^{+6}\) weeks

71 (71.7)

37 (69.8)

Infertility treatments

15 (15.2)

9 (17.0)

0.951

Gestational diabetes

16 (16.2)

10 (18.9)

0.844

Gestation at sample (weeks), \(mean \pm SD\) (range)

 \(<16^{+0}\) weeks

\(12^{+4}\pm 1^{+5}\) (\(6^{+2}\)–\(15^{+4}\))

\(12^{+5}\) \(\pm\) \(1^{+6}\) (\(8^{+2}\)–\(15^{+3}\))

0.439

 \(16^{+0}\)–\(24^{+0}\) weeks

\(20^{+0}\pm 2^{+1}\)(\(16^{+1}\)–\(23^{+4}\))

\(20^{+1}\pm 1^{+6}\) (\(16^{+1}\)–\(23^{+4}\))

0.894

Intervention

 Progesterone

34 (34.3)

25 (47.2)

0.170

 Cerclage

44 (44.4)

21 (39.6)

0.689

Post-intervention samples

 Post-progesterone samples\(^{b}\)

25/198 (12.6)

19/106 (17.9)

0.280

 Post-cerclage samples\(^{b}\)

36/198 (18.2)

14/106 (13.2)

0.341

 GA at delivery, weeks, median (range)

\(39^{+0}\) (\(37^{+0}\)–\(41^{+0}\))

\(26^{+6}\) (\(16^{+3}\)–\(36^{+4}\))

< 0.001