Congenital syphilis. Stillborn syphilitic baby with characteristic skin peeling (desquamation). Syphilis is caused by the bacterium Treponema pallidum. The congenital form is passed from a pregnant mother to her child across the placenta. Once the foetus is infected, the bacteria multiply rapidly, invading and damaging nearly all of the tissues and organs of the unborn infant. Between 40%-70% of women with active syphilis will give birth to a syphilis-infected baby, 50% of which will either be stillborn or die shortly after birth.