Prenatal Stage Sensitivity to Teratogens

During the prenatal period, a developing fetus undergoes various stages which are critical for its subsequent physical and neurological development. These stages can be influenced by numerous external factors, including maternal health, nutrition, and environmental exposures. One specific period in prenatal development is known for its heightened sensitivity to teratogens. Which of the following stages of prenatal development is characterized by the greatest risk for the effects of teratogens?