Prenatal Stage:
The prenatal stage refers to the period of development before birth, during which a human or animal embryo/fetus grows and undergoes significant physical and physiological changes.

1. Germinal Stage: The first two weeks of prenatal development, characterized by the fertilization of the egg and its subsequent implantation into the uterus.

2. Embryonic Stage: Lasting from the end of the germinal stage to the eighth week after conception, this stage is marked by the rapid formation of the major organs and basic body structures.

3. Fetal Stage: Beginning from the ninth week after conception and continuing until birth, this stage involves further development and maturation of organs and systems, as well as substantial growth in size and weight.

Key Events:
1. Cell Division and Implantation: During the germininal stage, the fertilized egg undergoes multiple divisions to develop into a blastocyst. It then attaches to the wall of the uterus.

2. Organogenesis: Throughout the embryonic stage, the foundation of major organs, such as the heart, brain, lungs, and limbs, is laid down. Differentiation of tissues and organ development occur rapidly.

3. Growth and Refinement: In the fetal stage, the organs and bodily systems continue to mature and refine. There is rapid growth in size and weight as the fetus gains muscle mass and accumulates adipose tissue.

The prenatal stage is a crucial period during which the foundation is laid for an individual’s lifelong health and development. It is influenced by various factors, including genetics, maternal health, nutrition, and environmental exposures. Understanding this stage helps identify potential risks and allows for interventions to ensure optimal prenatal health and well-being.