Table 1

Clinical and cost parameters for model comparing single screening with universal repeat screening of syphilis in pregnancy in the UK

Baseline valueLowHighDistributionNote
Clinical parameters
Total number of women in model (representing 1 year)725 891Based on number of deliveries in the UK in 2017/2018 and the screening uptake. See online supplemental table S6.
Probability of having syphilis at the start of pregnancy0.000350.000280.00042BetaData derived from 2011 SASS data13 (England only (244/691,494)).
Assume same risk in other UK countries.
Probability of becoming infected with syphilis during pregnancy0.0000170.00000170.00012BetaIncidence was estimated using published incidence and prevalence data from USA scaled to reflect UK prevalence.13 32
Probability of receiving syphilis screen before 28 weeks gestation0.9470.9360.984BetaEstimate based on gestational week at first antenatal attendance. See online supplemental table S7. The low value is in line with results from SASS study.13 The high value is in line with data from Northern Ireland which (from the UK countries) has the highest proportion of women attending before 28 weeks.
Probability of true positive result0.9950.9841.00BetaBased on the average test sensitivity of five EIA assays used in the UK. High and low values are based on best and worst test performance of assays used in the UK.28 29
Probability of false negative result‡0.0050.0160.00BetaBased on the average test sensitivity of five EIA assays used in the UK. High and low values are based on best and worst test performance of assays used in the UK.28 29
Probability of true negative result0.9980.9990.99BetaBased on average test specificity of five EIA assays (99.8%) used in the UK.
High and low are estimates.28 29
Probability of false positive result‡0.0020.0010.01BetaBased on average test specificity of five EIA assays (99.8%) used in the UK. High and low are estimates.28 29
Cost parameters (£)
Syphilis screen13.366.6826.72GammaEstimated using microcosting. Screening is performed at the same time as other antenatal blood tests—this would also be the case for repeat screening at 28 weeks gestation. See online supplemental table S8.
Management of women diagnosed with syphilis in pregnancy314.09251.27376.91GammaClinical management by sexual health clinician estimate based on London Integrated Sexual Health Tariff.33 See online supplemental table S9.
Intrauterine fetal demise (IUFD)*4356.803485.445228.16GammaEstimate based on 2013/2014 published estimate from UK inflated to 2017/2018 costs.34
Preterm delivery7100.375680.308520.45GammaEstimate based on UK costs for delivery at 32–33 weeks and 34–36 weeks gestation (inflated from 2010/2011 costs).35 UK data on gestational age at delivery (online supplemental table S10) were then used to calculate the proportion of deliveries at 32–33 (28%) and 34–36 weeks (72%).
Term delivery (37+ weeks)2034.621627.692441.54GammaEstimate based on published cost using inflated 2010/2011 UK data.35
Neonatal death†5805.804644.646966.96GammaEstimated using cost of IUFD plus additional hospital costs. See online supplemental table S11.
CS testing and treatment6607.685286.147929.21GammaEstimated using microcosting. See online supplemental tables S12 and S13.
CS neonatal screen245.25196.20294.30GammaScreening test for neonates born to women treated for syphilis in pregnancy. Estimated using microcosting. See online supplemental table S14.
CS lifetime healthcare cost80 423.37GammaAverage additional lifetime healthcare costs attributable to CS based on cost estimate for cerebral palsy (estimate from 2000).22
CS lifetime health and social care cost651 387.47GammaAverage additional lifetime health and social costs attributable to CS based on cost estimate for cerebral palsy (estimate from 2000).22
  • For costs, high and low values are ±20% of baseline values with exception of syphilis screening cost where high and low values are ±50%.

  • *IUFD refers to the death of a baby in the uterus at ≥20 weeks gestation that is, stillbirth.

  • †Neonatal death refers to the death of a baby within the first 28 days after birth.

  • ‡These probabilities refer to the final diagnosis after all diagnostic testing plus discussion with sexual health consultant if diagnostic tests result is positive for treponemal antibodies.

  • CS, congenital syphilis; EIA, enzyme immunoassay; SASS, Surveillance of Antenatal Syphilis Screening.