Prison-based pregnancies face a preventable but growing threat that standard medical protocols are failing to catch. Congenital syphilis cases have surged nationwide, yet current screening practices miss critical windows when infections develop or recur during pregnancy, particularly affecting incarcerated women who face elevated transmission risks. A documented case from correctional healthcare reveals how routine entry screening can provide false security. An incarcerated pregnant woman tested negative for syphilis upon prison admission but showed positive results during third-trimester testing, narrowly preventing mother-to-child transmission through timely treatment. This near-miss illustrates a systemic gap: maternal seroconversion can occur after initial negative tests due to new infections or disease progression from undetectable early stages. The clinical reality challenges current practice standards that rely heavily on single-point screening. Correctional facilities house populations with disproportionate STI exposure risks, yet lack universal third-trimester re-screening protocols despite CDC recommendations for high-risk groups. This case adds weight to emerging evidence that repeat testing during late pregnancy could significantly reduce congenital syphilis transmission. The intervention represents a targeted prevention opportunity within a controlled healthcare environment where consistent monitoring is feasible. However, implementation requires policy changes and resource allocation in correctional healthcare systems already stretched thin. The findings suggest that universal third-trimester screening in carceral settings could serve as a model for broader high-risk population management, potentially preventing irreversible neurological and developmental damage in newborns from what remains an entirely treatable maternal infection.