Sikiökehitys

Sikiökehitys refers to the developmental stage of a human embryo or fetus from the time of conception until birth. This period is characterized by rapid cell division, differentiation, and the formation of all major organ systems. Following fertilization, the zygote undergoes cleavage and forms a blastocyst, which implants in the uterine wall. The embryonic period, typically lasting until the eighth week of gestation, sees the development of the basic body plan, including the neural tube, heart, limbs, and facial features. During this time, the embryo is particularly vulnerable to environmental factors.

The fetal period begins around the ninth week and continues until birth. In this phase, the developing organism is called a fetus. The focus shifts from organ formation to growth and maturation. Organs mature and become functional, and the fetus gains weight and size. Movements become more coordinated, and sensory organs develop. External genitalia become distinguishable. By the end of the third trimester, the fetus is generally capable of surviving outside the womb, although significant development continues. Sikiökehitys is a continuous and complex process governed by genetic instructions and influenced by maternal health and nutrition.