Section 3.1 Prenatal development

The fetal stage is the final phase of prenatal development, beginning around the 8th week after conception and continuing until birth. At this point, the developing organism is referred to as a fetus. This stage is marked by rapid physical growth, as the fetus increases in size from about 1 inch and 1/4 ounce to an average birth weight of around 7 pounds and a length of approximately 20 inches.

Throughout this stage, all of the organ systems formed during earlier development undergo further refinement and maturation to prepare for life outside the womb. One of the most critical milestones during this period is the achievement of viability, or the fetus’s ability to survive independently outside the womb. This can occur as early as 23 weeks, though most medical experts consider 24 weeks as the average threshold, primarily due to improved lung and brain development.

Brain development is especially significant during the fetal stage. Between the 10th and 18th weeks, brain cells multiply rapidly, laying the foundation for neurological function after birth. The continued growth and specialization of the brain and other vital systems ensure that the fetus is equipped to respond to its environment and sustain life once born.