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 
10.223.6 
12.1 
8.417.5 
11.7 
8.316.6 
1.10 
0.761.59 
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:10.1186/14712393512 