Final answer:
Fetal viability is the ability of the fetus to survive outside the uterus, which is generally possible after 23 weeks of gestation, with better chances after 26 weeks. By week 37, organ systems are sufficiently developed to support life outside the womb.
Step-by-step explanation:
Fetal viability refers to the stage at which the fetus can live independently of the mother's body, outside the uterus. A fetus is considered a prenatal human between the embryonic stage and birth, typically from week 9 to about week 38 after fertilization. During the fetal stage, significant development occurs, including the maturation of organ systems and the ability of the fetus to move within the amniotic fluid, which helps it prepare for life outside the womb.
At about 23 weeks of gestation, the survival chances of a premature infant are fairly low and require intensive medical care. By 25 weeks, the survival rate increases, and after 26 weeks, the likelihood of survival outside the uterus is much greater, with over 90% of babies being able to survive with proper medical attention. It is generally at week 37 that all of the organ systems are developed enough for the fetus to survive with fewer risks associated with premature birth.
The germinal stage, which is the earliest phase post-fertilization, lasts about a week until implantation in the uterus. In contrast, the fetal stage is marked by cell growth, differentiation, and the functioning of sensory systems. The fetus is adequately protected in the womb but must make drastic physiological changes during and after birth to adapt to the external environment.