Serological Responses and Pregnancy Outcomes in Women with Serofast Syphilis: Efficacy of Re-treatment in a Prospective Nested Case-Control Study

Background There are inconsistencies in guidelines concerning the necessity for anti-syphilis re-treatment during pregnancy for women who tested seropositive despite having received treatment before pregnancy. While global guidelines indicate that no further treatment is necessary, Chinese guidelines advocate for an additional treatment course. Methods A prospective nested case-control study was conducted to analyze serological responses and pregnancy outcomes in women with serofast syphilis, focusing on the effects of re-treatment. Results Out of 584 women with serofast syphilis, 537 (92.0%) experienced normal pregnancy outcomes, comparable to the 93.6% in women without syphilis. However, 47 (8.0%) faced adverse pregnancy outcomes (APOs), which included 8 (1.4%) spontaneous abortions, 2 (0.3%) intrauterine fetal deaths, and 37 (6.3%) instances of preterm birth or low birth weight. The rate of APOs showed no significant difference between those treated with benzathine penicillin G and those who were not (adjusted odds ratio [aOR], 0.59 [95% CI, 0.31–1.14]; P = 0.118). Among 462 newborns with follow-up, no congenital syphilis cases were identified. Serological responses were evaluated in 568 women, revealing that 74 (13.0%) experienced seroreversion of nontreponemal antibodies, 52 (9.2%) had a ≥ four-fold decrease in titers, 6 (1.0%) had a ≥ four-fold increase, and 436 (74.7%) maintained stable titers. No significant difference in seroreversion rates was found between the re-treated and non-re-treated groups (aOR, 1.43 [95%CI, 0.76-2.71]; P=0.271). Conclusions With adequate prenatal care and continuous monitoring of serological and symptomatic changes, it is unnecessary to re-treat serofast women exhibiting stable non-treponemal antibody titers during pregnancy.