Table 2 Mean gestational age at delivery by different methods and country, Pearson correlation and results from Bland Altman plots

Mean gestational age in weeks by US (95%CI)

38.73 (38.63–38.83)

38.85 (38.67–39.03)

38.37 (38.17–38.56)

39.27 (39.06–39.48)

38.74 (38.53–38.96)

 N

404

10

30

46

318

 Mean gestational age in weeks by LMP (95%CI)

38.41 (37.97–38.86)

40.80 (37.98–43.62)

38.61 (37.27–39.96)

40.26 (39.40–41.11)

38.05 (37.52–38.57)

 Pearson r

0.38

−0.06

0.66

0.05

0.38

 Mean difference in weeks

0.34

−1.81

−0.24

− 0.96

0.65

 95% limit of agreement

−7.9 to 8.6

−9.7 to 6.1

−5.6 to 5.1

−7.28 to 5.36

− 7.99 to 9.28

 Range of averages

25.21 to 50.14

37.86 to 44.64

27.93 to 43.00

36.07 to 44.14

25.21 to 50.14

 N

1624

382

581

289

372

 Mean gestational age in weeks by SFH (95%CI)

38.33 (38.16–38.50)

39.19 (38.91–39.46)

36.18 (35.95–36.41)

38.07 (37.71–38.42)

41.02 (40.69–41.36)

 Pearson r

0.63

0.7

0.87

0.54

0.58

 Mean difference in weeks

0.4

0.34

2.19

1.23

−2.28

 95% limit of agreement

−4.9 to 5.8

−4.2 to 3.5

−5.1 to 4.9

−3.86 to 6.33

−7.56 to 3.00

 Range of averages

22.14 to 46.85

29.50 to 44.21

22.14 to 43.64

29.79 to 45.71

29.14 to 46.86

 N

1538

379

553

242

346

 mean gestational age in weeks by BS (95%CI)

38.07 (38.05–38.09)

38.59 (38.55–38.64)

38.47 (38.44–38.50)

38.56 (38.52–38.59)

36.19 (36.16–36.22)

 Pearson r

0.31

0.35

0.52

0.45

0.16

 Mean difference in weeks

0.8

0.26

−0.03

0.83

2.7

 95% limit of agreement

−3.5 to 5.1

−3.6 to 4.1

−3.90 to 3.83

−2.30 to 3.95

−1.21 to 6.62

 Range of averages

28.79 to 43.21

29.50 to 42.86

28.78 to 43.21

32.64 to 41.64

32.93 to 40.43