Meconium is a thick, sticky greenish-black substance that is produced by the fetus in utero during the first few weeks of pregnancy. It consists mainly of swallowed amniotic fluid mixed with hair, skin cells, and other debris from the placenta. Meconium is typically expelled from the baby's body during the first bowel movement after birth (also known as the meconium passage). The presence or absence of meconium can provide important information about a newborn’s health.