Syphilis in Pregnancy

Syphilis is caused by the spirochete *Treponema pallidum* subspecies *pallidum*. During pregnancy, the organism can cross the placenta; transmission can also occur at delivery when the infant contacts an infectious genital lesion. Because organisms circulate in higher numbers during early infection, untreated maternal transmission risk is approximately greater than 70% with primary or secondary disease, about 40% with early latent disease, and under 10% with late latent disease. That lower risk in late latent infection is not a safe-risk category. Untreated or inadequately treated infection can still cause miscarriage, fetal growth restriction, non-immune hydrops, preterm birth, stillbirth, neonatal death, and ocular, neurological, hepatosplenic, or musculoskeletal disease in a surviving infant. Canada has seen a marked rise in congenital syphilis since 2018, so a single early prenatal screen cannot be treated as sufficient protection in every setting. The clinical model is straightforward: establish the maternal stage, give the stage-appropriate penicillin course without delay, complete it early enough to protect the fetus, and follow both maternal titres and the infant’s findings. A reactive syphilis result is the beginning of that process, not...