Fetal syphilis: clinical and laboratory characteristics

Objective: To examine the pathophysiology of fetal syphilis and correlate hematologic, immunologic, and sonographic findings. Methods: Twenty-four women with untreated syphilis during pregnancy were prospectively identified. Sonography with amniocentesis and percutaneous umbilical blood sampling were performed. Darkfield examination, rabbit infectivity testing, and polymerase chain reaction for detection of Treponema pallidum were performed on amniotic fluid. Hematologic and chemical testing of fetal blood was performed using standard techniques. Fetal antitreponemal IgM was detected by Western blot assay. Maternal syphilis was treated with 2.4 to 4.8 million units of benzathine penicillin G intramuscularly. Neonatal outcomes and signs of congenital syphilis were recorded. Results: Six women had primary, 12 had secondary, and six had early latent syphilis. Sixty-six percent of fetuses (95% confidence interval [CI] 47%, 82%) had either congenital syphilis or detection of Treponema pallidum in amniotic fluid. Sixty-six percent had hepatomegaly, including three fetuses (12.5%, 95% CI 4%, 31%) with ascites. Fetal antitreponemal IgM was detected in three cases. Abnormal liver transaminases were found in 88% (CI 69%, 96%), anemia in 26% (CI 13%, 47%), and thrombocytopenia in 35% (CI 19%, 55%). Maternal treatment was successful in 83% (CI 64%, 93%). Risk of treatment failure was significantly increased when hepatomegaly and ascites were present ( P = .01). Conclusion: Findings with fetal syphilis are similar to those of neonatal syphilis. We hypothesize that fetal transaminase elevation occurs early in the course of infection; hematologic abnormalities and hydrops occur later. Severity of disease may be associated with risk of treatment failure.