Fötus

Fötus is a term used in biology and medicine to describe the stage of development of a human or animal embryo from the time when the major organs and body structures have formed until birth. This developmental period typically begins around the ninth week of gestation after fertilization and extends through the remainder of the pregnancy. Prior to this stage, the developing organism is referred to as an embryo.

During the fetal stage, the primary focus of development shifts from the formation of basic structures to growth and maturation of existing organs and systems. The fetus gains weight, and its features become more refined. For instance, in human development, the sex organs differentiate, fingernails and toenails grow, and the brain continues to develop rapidly. The fetus also begins to move within the uterus, and these movements can often be felt by the mother.

The duration of the fetal stage varies depending on the species. In humans, a full-term pregnancy is typically around 40 weeks from the last menstrual period, meaning the fetal stage lasts for approximately 31 weeks. The health and well-being of the fetus are crucial for a successful pregnancy, and various medical interventions and monitoring techniques are employed to ensure proper development. The term "fetus" is derived from the Latin word for "offspring" or "young."