Final answer:
By the 16th to 20th weeks of gestation, fetal development has progressed significantly, with the fetus taking on more defined human traits, shedding lanugo, and developing thicker head hair and vernix. Newborns emerge with distinctive proportions, and may still have traces of protective coverings such as vernix and lanugo. The newborn's appearance at birth closely resembles its development in the later stages of pregnancy.
Step-by-step explanation:
Embryonic Development and Appearance at Birth
A newborn's appearance, very similar to what it will be at birth, starts developing early on during pregnancy. We all start as a single cell, and through the process of embryonic and fetal development, the human features gradually take shape. By approximately the 16th to 20th weeks of pregnancy, a fetus has grown enough that the mother may notice quickening, or fetal movements, which occur as the fetus starts to take on a more defined human shape with powerful limb movements. Despite starting with similar embryonic appearances, distinct individual traits begin to emerge early on.
During this period, features such as a fetus's head hair starts to grow thicker, and they shed the lanugo—a soft, downy hair that covers the skin of the fetus. The fetus's skin is also coated with a waxy vernix, which protects and moisturizes the skin. By the time of birth, many newborns will have lost the vernix and lanugo, although some may still exhibit traces of these protective coverings.
Newborns typically have distinctive body proportions with a larger head relative to the rest of the body, and may have varying amounts of head hair. Their skin is wet and may have traces of blood and vernix, with possible peeling on extremities. Despite the remarkable changes from conception to birth, newborns' features may still recall the embryonic stages, with wide shoulders, hips, and long limbs.