Final answer:
The lowest chances of being affected by a teratogen occur during the embryonic stage of pregnancy.
Step-by-step explanation:
The time period that reflects the lowest chances of being affected by a teratogen is during the early stages of pregnancy, specifically the embryonic stage. This is the time when the major organs are forming, and exposure to harmful substances can cause damage to the developing body systems. It is especially important for a pregnant woman to avoid exposure to toxins during this time, typically the first eight weeks after fertilization.