Table 3.

 Interventions in each maternal risk group with a probability of being cost effective of at least 1%*

Maternal risk groups in hierarchical order	% of total population	Intervention	Probability of being cost effective	Expected value of information per year in UK
Preterm deliveries (<37 weeks)
1. Planned caesarean section	0.80	IV antibiotic	0.5870	£5 281 333
		Oral antibiotic	0.4120
2. Previous baby with GBS	0.01	IV antibiotic	0.8590	£7 820
		Oral antibiotic	0.1370
3. Positive urine or vaginal swab for GBS in current pregnancy	0.44	IV antibiotic	0.9730	£81 600
		Oral antibiotic	0.0178
4. Fever ≥38.0°C in labour	0.25	IV antibiotic	0.7800	£539 467
		Oral antibiotic	0.2160
5. Rupture of membranes before onset of labour	2.41	IV antibiotic	0.5800	£12 806 667
		Oral antibiotic	0.4190
6. Spontaneous labour (membrane rupture <2 hours before or after onset of labour)	3.43	IV antibiotic	0.8590	£4 193 333
		Oral antibiotic	0.1370
Term deliveries (≥37 weeks)
7. Planned caesarean section	7.99	Oral antibiotic	0.6720	£1 586 667
		IV antibiotic	0.3270
8. Previous baby with GBS	0.08	IV antibiotic	0.6060	£30 600
		Oral antibiotic	0.3930
9. Positive urine or vaginal swab for GBS in current pregnancy	3.51	IV antibiotic	0.9730	£68 000
		Oral antibiotic	0.0242
10.Fever ≥38.0°C in labour	1.60	IV antibiotic	0.7170	£581 400
		Oral antibiotic	0.2720
		PCR testing, IV antibiotic	0.0102
11. Membrane rupture for ≥18 hours	8.37	PCR testing, IV antibiotic	0.5760	£4 533 333
		Culture testing, IV antibiotic	0.2000
		PCR testing, oral antibiotic	0.1820
		Culture testing, oral antibiotic	0.0418
12. No risk factors	71.10	Culture testing, IV antibiotic	0.8390	£2 040 000
		PCR testing, IV antibiotic	0.0952
		Nothing	0.0640

*Culture testing not listed for risk groups 1-10 because of zero probability of being cost effective.

GBS=group B streptococcal infection. IV=intravenous. PCR=polymerase chain reaction.