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How can syphilis pass from a pregnant woman to a fetus?

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Scanning electron micrograph of Treponema pallidum, the spirochete bacterium that is the causative agent of syphilis. — syphilis Scanning electron micrograph of *Treponema pallidum*, the spirochete bacterium that is the causative agent of syphilis.

Syphilis is transmitted from an infected pregnant woman to her fetus through the placenta, which serves as the pathway for the infectious agent to enter the fetal circulation.1

This transmission is most likely to occur if the mother becomes infected during pregnancy, though an untreated infection acquired prior to pregnancy also poses a significant risk to the fetus. If left untreated, the infection can lead to severe consequences, including miscarriage, stillbirth, or the birth of an infant with congenital syphilis, which may manifest as rashes, pneumonia, skeletal abnormalities, and long-term damage to the central nervous system.231

It is a vital ethical imperative to recognize that these devastating outcomes are preventable. The use of antibiotics, such as penicillin, is highly effective at treating the infection in the mother and preventing its transmission to the fetus.32