embryoperiode

The embryoperiode, or embryonic period, is a stage in the development of animals, including humans, during which the embryo undergoes rapid growth and the foundations of organ systems are laid down. The term distinguishes this early, formative phase from later fetal development.

In humans, the embryonic period begins with fertilization and ends at the end of the eighth week after fertilization (approximately the end of the second month of pregnancy). The first two weeks are often referred to as the pre-embryonic period. During the embryonic period, key developmental processes occur, including gastrulation, neurulation, and organogenesis. The three germ layers—ectoderm, mesoderm, and endoderm—are established, the neural tube forms, the heart begins to beat, limb buds appear, and the primordia of major organ systems develop.

Because this period involves rapid morphogenesis and organ formation, it is considered a critical window for congenital anomalies. Genetic factors, teratogens, nutritional status, and environmental influences can have profound effects on development during this time. Disruptions can lead to structural birth defects or functional impairments.

After the embryonic period, development proceeds into the fetal period, characterized by growth and maturation of already formed organ systems until birth. Although most essential structures are established by the end of the embryonic period, later development continues to refine and expand organ function throughout gestation.

The concept of the embryonic period applies across vertebrates, with timing and details varying by species. In embryology, Carnegie stages are commonly used to describe morphological progress from fertilization through the end of the embryonic period.