What is the initial stage of human development following fertilization?

The initial stage of human development following fertilization is the zygote. A zygote is formed when the sperm and egg merge, creating a single-cell entity with a unique genetic makeup. This stage marks the very beginning of the developmental process, where the genetic material from both parents combines.

Following this stage, the zygote undergoes several rounds of cell division, leading to the formation of a blastocyst, which then implants into the uterine wall. The embryo stage follows this as the cells further differentiate and develop into specific tissues and organs. The fetus stage comes later in development, after the embryo has established many of the major systems and structures. Thus, the zygote represents the first stage in this intricate process of human development.