At what stage of development is the human embryo most susceptible to teratogens?

At what stage of development is the human embryo most susceptible to teratogens?

Step 1: Understand what a teratogen is. A teratogen is something that can cause birth defects in a developing embryo or fetus.
Step 2: Learn about the stages of human development. The development of a human embryo is divided into three trimesters.
Step 3: Focus on the first trimester. The first trimester is the first three months of pregnancy.
Step 4: Recognize that during the first trimester, major organs and body systems are forming in the embryo.
Step 5: Conclude that because the major organs are developing during this time, the embryo is most vulnerable to teratogens in the first trimester.

Teratogens – Substances that can cause developmental malformations in an embryo or fetus.
Embryonic Development Stages – The stages of development in an embryo, particularly the first trimester when major organs are forming.
Critical Periods – Specific times during development when the embryo is particularly vulnerable to environmental factors.