<prompt> Treponema pallidum crosses placenta:After 36 weeksAfter 28 weeksAfter 2nd trimesterAt any stage of pregnancy  <response>: Transmission of Treponema pallidum from an infected woman to her fetus across the placenta may occur at any stage of pregnancy, but the lesions of congenital syphilis usually develop after-the 4th month of gestation, when fetal immunologic competence begins to develop. 