Uptake of prenatal syphilis screening and its determinants in Ontario, Canada: a population-based retrospective cohort study

<sec><title>Background:</title> Timely prenatal syphilis screening is critical for preventing congenital syphilis infection. We aimed to examine prenatal syphilis screening patterns in Canada and to identify factors associated with missed or late screening. </sec><sec><title>Methods:</title> For this population-based retrospective cohort study, we used linked provincial administrative health data from Ontario, Canada. We included pregnancies (> 20 wk gestation) resulting in live births or stillbirths from January 2018 to December 2023. Missed prenatal syphilis screening (at any point during pregnancy or at delivery) or late screening (either during the third trimester or at delivery) were the primary outcomes. We evaluated individual-level and external factors associated with the outcomes using modified Poisson regressions with generalized estimating equations. We reported adjusted relative risks (RRs) and 95% confidence intervals (CIs). </sec><sec><title>Results:</title> Among 551 706 pregnancies (median maternal age 31 yr, interquartile range 28 to 34 yr), 507 169 (91.9%) were screened for syphilis, and 435 162 (78.9%) received first-trimester screening. Screening rates increased over time and varied by geography and individual risk factors. Those tested for syphilis within 1 year before conception were more likely to miss screening during pregnancy (adjusted RR 2.12, 95% CI 2.08 to 2.16). Initial screening at delivery was associated with being younger (15 to 19 yr v. 30 to 39 yr) at conception (adjusted RR 4.01, 95% CI 3.33 to 4.81), having injection or general drug use within 3 years before conception (adjusted RR 3.78, 95% CI 3.11 to 4.59), and living in a neighbourhood of the lowest income quintile (adjusted RR 1.59, 95% CI 1.40 to 1.80). Similar factors were associated with initial screening during the third trimester. </sec><sec><title>Interpretation:</title> In Ontario, 1 in 5 pregnancies did not receive timely first-trimester screening for syphilis, and we identified sociodemographic and behavioural factors associated with late screening. These findings point to modifiable gaps in system and service delivery and highlight the need for coordinated clinical, public health, and community-based strategies to improve coverage and timeliness of prenatal syphilis screening. </sec>