Table 3

Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive and negative likelihood ratios with 95% confidence intervals for screening at 32 weeks or 36 weeks, using low vaginal (LVS) and/or perianal (PAS) swabs for 600 women and for using a risk factor strategy*.

32 Weeks (n = 600)

36 Weeks (n = 600)

(n= 699)

LVS

PAS

Either

LVS

PAS

Either

Estimate + 95% CI

Estimate + 95% CI

Estimate + 95% CI

Estimate + 95% CI

Estimate + 95% CI

Estimate + 95% CI

Estimate + 95% CI

Sensitivity

63

54–71

70

61–77

72

63–79

73

65–81

76

67–83

81

73–87

19

13–26

Specificity

94

92–96

94

91–96

93

90–95

95

93–97

94

91–96

93

90–95

83

79–86

PPV*

77

68–84

76

68–84

75

66–82

82

74–88

78

70–85

77

69–84

25

18–34

NPV

90

87–92

91

89–94

92

89–94

92

90–95

93

90–95

94

92–96

77

73–80

Likelihood ratio (+ve)

11.3

7.6–16.7

11.2

7.7–16.2

10.1

7.2–14.3

15.5

10.2-23.6

12.1

8.4-17.5

11.7

8.3-16.6

1.10

0.76-1.59

Likelihood ratio (-ve)

0.39

0.31–0.49

0.32

0.25–0.42

0.30

0.23–0.40

0.28

0.21–0.37

0.26

0.19–0.35

0.21

0.15–0.29

0.98

0.90–1.06

Diagnostic Odds Ratio

28.7

16.4–50.6

34.5

19.8–60.4

33.4

19.4–57.9

55.4

30.1–103

46.5

26.1–83.1

56.7

31.4–103

1.12

0.69–1.79

* Risk factor strategy included women with GBS bacteruria at booking, birth at <37 weeks' gestation, prelabour rupture of membranes or temperature during labour of greater than or equal to 38 degrees Centrigrade.

Hiller et al. BMC Pregnancy and Childbirth 2005 5:12   doi:10.1186/1471-2393-5-12