What is the pre-embryonic stage, and what are its milestones?

A) Weeks 1-2: Fertilization, implantation, formation of the blastocyst
B) Weeks 3-8: Differentiation of major organs and structures, beginning of heartbeat
C) Weeks 9-12: Rapid growth and maturation of organs, formation of limbs and digits
D) Weeks 13-38: Continued growth and development, preparation for birth

The pre-embryonic stage encompasses the first two weeks post-fertilization, defined by milestones such as fertilization, implantation, and the formation of the blastocyst. So the correct option is: A) Weeks 1-2; fertilization, implantation, formation of the blastocyst

Explanation:

The pre-embryonic stage refers to the first two weeks of prenatal development following fertilization. The correct milestones associated with this stage are A) Weeks 1-2; fertilization, implantation, formation of the blastocyst. During these initial two weeks, the zygote undergoes several mitotic cell divisions, becoming a multicellular entity known as the blastocyst, which then implants itself in the lining of the uterus. This stage lays the foundation for the subsequent stages of embryonic and fetal development.