Lanugo

n. covering of fine soft hairs, coating of down (especially on a newborn infant)

Lanugo refers to hair that grows on the body in an attempt to insulate the skin because of lack of fat. It is a type of pelage. Lanugo is very fine, and may grow densely on the body in places where significant amounts of hair does not normally grow. Lanugo occurs on fetuses as a normal part of gestation. Lanugo hair is usually shed and replaced by vellus hair at ~40 weeks of gestational age. As the lanugo is shed from the skin, it is 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.
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Lanugo /la·nu·go/ the fine hair on the body of the fetus. la·nu·go n. pl. la·nu·gos The fine, soft hair that grows on a fetus and is present on a [more]Lanugo - Community and Resources

Noun
1. the fine downy hair covering a human fetus; normally shed during the ninth month of gestation
(hypernym) down, pile

n. lanugo, soft hairs, down (especially on a newborn infant)