Lanugo's fine, downy hair; it's a type of pelage. In humans Fetal development Lanugo grows on fetuses as a normal part of gestation, but's usually shed and replaced by vellus hair at about 40 weeks of gestational age. As the lanugo's shed from the skin, it's normal for the developing fetus to consume the hair with the fluid, since it drinks from the amniotic fluid and urinates it back into its environment. Subsequently, the lanugo contributes to the newborn baby's meconium. The presence of lanu… (More on Lanugo)