Abstract: Background　Syphilis mother-to-child transmission causes hundreds of thousands of adverse pregnancy outcomes globally each year, with China's prevention and control situation being particularly severe. Although penicillin treatment during pregnancy is the core strategy, controversies persist regarding the optimal timing of treatment, the management of serofast populations, and the effectiveness of standardized protocols.Objective　To evaluate the effect of different treatment regimens on serological outcomes in infants born to mothers with syphilis, and explore the clinical implications of variations in treatment timing and duration. Methods　A retrospective cohort study design was performed in pregnant women with syphilis infection in Changzhou from January 2015 to December 2019, and the patients were categorized into untreated group, single-course group, and double-course group according to different intervention methods. The time of syphilis-specific antibody conversion in infants, time of infection exclusion and changes in maternal non-specific antibody titers were compared among the groups by stratified analysis. Results　There were no statistically significant differences in demographic characteristics such as age, ethnicity, education level, marital status, syphilis stage, and mode of infection among the three groups (P>0.05). However, significant difference was found in the reduction of serum titers among pregnant women in the untreated group (n=145), single-course treatment group (n=116), and double-course treatment group (n=148) (P0.05). The therapeutic benefits for pregnant women with fixed serum titers were limited, and there was no significant difference in the time to seroconversion of antibodies in their newborns compared to the untreated group (P>0.05). The difference in titer reduction between the high titer group and the low titer group was significant (P<0.001), mainly manifested in the high titer group, where titer reduction was significant after receiving single-course and double-course treatments 0 (0,1), 1 (0,3). Using factorial ANOVA combined with the Bootstrap resampling method (each factor combination subgroup was sampled 80 times for validation), it was found that the interaction between different treatment intensities and high/low titer levels was extremely significant (P<0.001). Moreover, in the high-titer group, more pronounced titer changes were observed with increasing treatment intensity, resulting in greater patient benefits, which aligns with clinical practice.Conclusion　Completion of a full course of penicillin therapy prior to delivery accelerates the recovery of serologic conversion in infants, but the need for therapy in serofixed pregnant women also needs to be reassessed.