Amniotic fluid contains fetal urine (from swallowed amniotic fluid) and occasionally meconium: baby's first feces, composed of mucus, bile, epithelial cells, shed fetal hair, and other amniotic detritus. The Wikipedia entry helpfully contrasts the tarry, olive-brown smear of meconium--photographed in a tiny disposable diaper--with the similarly posed yellowish excretion of a breast-fed newborn, both with an option for viewing in the magnified resolution of 1,280 x 528 pixels.