During which time period is the fetus most vulnerable to teratogens?

The correct time period during which the fetus is most vulnerable to teratogens is from 2 to 8 weeks of gestation. This period is known as the embryonic stage of development, during which critical organogenesis occurs. All major organ systems begin to form during this time, making the developing fetus especially sensitive to harmful substances, referred to as teratogens. Exposure to teratogens during this stage can lead to significant developmental abnormalities or malformations.

During the embryonic period, the rapidly dividing and differentiating cells are much more prone to disruption from teratogens like alcohol, certain medications, infections, and environmental toxins. The effects of teratogen exposure can significantly vary depending on the timing of exposure, the type of teratogen, the dosage, and the genetic susceptibility of the fetus.

The other time periods mentioned in the options encompass stages where certain structures are less vulnerable, as some organ systems are already formed by those weeks and more mature stages of development are underway. Therefore, the period from 2 to 8 weeks is critically important and is recognized as the peak vulnerability window for teratogenic effects on fetal development.