Meconium is the earliest
stool of a mammalian
infant. Unlike later feces, meconium is composed of materials ingested during the time the infant spends in the
uterus: intestinal
epithelial cells,
lanugo,
mucus,
amniotic fluid,
bile, and water. Meconium, unlike later feces, is viscous and sticky like tar, its color usually being a very dark olive green; it is almost odorless. When diluted in amniotic fluid, it may appear in various shades of green, brown, or yellow. It should be completely passed by the end of the first few days after birth, with the stools progressing toward yellow (digested milk).