## **Core Concept**
Treponema pallidum, the causative agent of syphilis, can be transmitted from mother to fetus during pregnancy, a condition known as congenital syphilis. This transmission can occur at any stage of pregnancy if the mother is infected.

## **Why the Correct Answer is Right**
The transmission of Treponema pallidum to the fetus can occur as early as the **second trimester**, but it is well established that the risk of transmission increases with the gestational age. However, vertical transmission (from mother to fetus) can technically occur at any point after the spirochetes enter the maternal bloodstream and cross the placenta. The critical period for potential transmission starts once the maternal infection has become established.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a specific timeframe but does not accurately reflect the earliest possible transmission window.
- **Option B:** This option might suggest a later timeframe than necessary for potential transmission.
- **Option C:** This option might seem plausible but does not accurately represent the earliest timeframe for potential transmission.
- **Option D:** This option indicates a later gestational age than necessary for transmission to occur.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **congenital syphilis can occur with maternal syphilis of any stage** and that prevention of congenital syphilis relies on **screening of all pregnant women** for syphilis early in pregnancy. Early detection and treatment of syphilis in pregnant women can prevent congenital syphilis.

## **Correct Answer:** . **16-28 weeks**