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Table 3. Summary of benefits and harms of screening 1000 high-risk pregnant women for bacterial vaginosis1

Benefit and relevant factors "General" high-risk groupa "More selected" high-risk groupb
Assumptions
Proportion of pregnant women who meet screening criteria 0.1 0.03
Prevalence of BV in population 0.25 0.25
Relative risk of PTD in BV patients 1.6 1.6
Sensitivity of screening test 0.95 0.95
Specificity of screening test 0.95 0.95
Adherence to treatment 0.8 0.8
Effect sizes, BV patients (probability: control group vs treated group [CI])c
PTD <37 weeks -0.075(-0.19 to +0.04) +0.22(+0.13 to +0.31)
PPROM -0.04(-0.101 to +0.03) +0.29(+0.15 to +0.43)
PTD <34 weeks +0.012(-0.06 to 0.08) +0.06(+0.01 to +0.15)
Effect sizes, patients without BV (probability: control group vs treated group)c
PTD <37 weeks 0 0
PPROM 0 0
PTD <34 weeks -0.02 -0.06
Results (n)
Patients with unsuspected BV 250 250
Correctly diagnosed with BV 238 238
BV patients who complete therapy 190 190
BV patients with missed diagnosis 13 13
Incorrectly diagnosed with BV 38 38
Outcomesc
Decrease or increase in PTD <37 weeks (CI) -14(-36 to +7) +42(+25 to +59)
Decrease or increase in PPROM -8(-19 to +4) +49(+28 to +70)
Decrease or increase in PTD <34 weeks +2(-11 to +14) +9(-2 to +19)
a Screen all women who have at least one previous PTD.
b Screen if there is more than one previous PTD or other risk factors.
c Minus sign indicates a net increase, plus indicates a net decrease, in adverse effects.
1 BV, bacterial vaginosis; PTD, preterm delivery; CI, confidence interval; PPROM, preterm premature rupture of membranes.

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