What changes characterize the fetal period of human prenatal development?

The fetal period of human prenatal development begins at approximately the eighth week after conception and continues until birth. While the preceding embryonic period is defined by organogenesis—the formation of major organ systems—the fetal period is primarily characterized by the rapid growth of the body and the maturation of tissues and organs.123

Key changes during this stage include:

• Physical Growth and Proportions: The fetus undergoes dramatic increases in size and weight. While the head remains disproportionately large due to rapid brain development, body proportions gradually improve as the fetus matures.24
• Functional Development: The fetus progressively assumes physical functions. By the 20th week, fetal movements ("quickening") are typically felt by the mother. By the 32nd week, the fetus is generally capable of breathing, sucking, and swallowing, and by the 36th week, it can respond to light and sound.42
• External Features: Over time, the skin becomes less transparent and is covered by downy hair (lanugo) and a protective greasy substance (vernix caseosa). Features such as eyebrows, eyelashes, and nails develop, and the face becomes increasingly distinct.4
• System Maturation: Internal organs continue to specialize and refine their functions, preparing the fetus for life outside the womb.43