This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Treponema pallidum crosses placenta: 
Select and explain. 
A. After 36 weeks, B. After 28 weeks, C. After 2nd trimester, D. At any stage of pregnancy
D: At any stage of pregnancy
Answer: D: At any stage of pregnancy 
Explanation: 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.