What is a Fetus?
A fetus is the developmental stage of a human offspring from the end of the 8th week after fertilization (or 10th week of gestation) until birth. During this period, the major body structures are already formed and the focus of development shifts to growth and maturation of these systems.
Transition from Embryo to Fetus
The fetal stage begins after the embryonic stage, which covers the first 8 weeks post-fertilization. The embryonic period is characterized by rapid cell division, differentiation, and the formation of major organs and body plans. Once these basic structures are in place, the developing organism is termed a fetus.
Fetal Development Milestones
During the fetal stage, the organism undergoes significant growth. For example, by the end of the first trimester (around 12 weeks), the fetus is typically about 3 inches long and all major organ systems are present, though not fully functional. Subsequent months see the development of reflexes, sex organ differentiation, lung maturation, and substantial weight gain, preparing the fetus for life outside the womb.
Significance in Human Biology
Understanding the fetal stage is crucial in obstetrics and prenatal care. Monitoring fetal development allows healthcare providers to assess health, detect potential complications, and ensure optimal conditions for growth. It highlights the complex biological processes that transform a structured embryo into a fully formed infant capable of independent survival.