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Meconium from 12-hour-old newborn — the baby's third bowel movement. Scale: 5 cm left to right.

Meconium is the first stool of an infant, composed of materials ingested during the time the infant spends in the uterus: Intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. Meconium is sterile, unlike later feces, is viscous and sticky like tar, and has no odor. It should be completely passed by the end of the first few days of postpartum life, with the stools progressing toward yellow (digested milk). The term Meconium derives from meconium-arion, meaning "opium-like", in reference either to its tarry appearance or to Aristotle's belief that it induces sleep in the fetus.^[1]

Meconium is normally stored in the infant's intestines until after birth, but sometimes it is expelled into the amniotic fluid prior to birth or during labor and delivery.

Meconium can be tested for various drugs, to check for in utero exposure. In the USA, the results of meconium-testing run on a newborn can be turned in to child protective services and other law enforcement agencies.^[2]

Sometimes the meconium becomes thickened and congested in the ileum, a condition known as meconium ileus. Meconium ileus is often the first symptom of cystic fibrosis.^[3] In cystic fibrosis, the meconium can form a bituminous black-green mechanical obstruction in a segment of the ileum. Beyond this there may be a few separate grey-white globular pellets. Below this level, the bowel is a narrow and empty micro-colon. Above the level of the obstruction, there are several loops of hypertrophied bowel distended with fluid. No meconium is passed, and abdominal distension and vomiting appear soon after birth. About 20% of cases of cystic fibrosis present with meconium ileus, while approximately 20% of one series of cases of meconium ileus did not have cystic fibrosis.^[4] The presence of meconium ileus is not related to the severity of the cystic fibrosis.^[5] The obstruction can be relieved in a number of different ways.^[6]

Meconium ileus should be distinguished from meconium plug syndrome, in which a tenacious mass of mucus prevents the meconium from passing.

• In biology, meconium describes the metabolic waste product from the pupal stage that is expelled through the anal opening of the adult butterfly upon eclosion from the chrysalis.

• Meconium aspiration syndrome (MAS), a condition in which infants take meconium into their lungs before or during delivery

1. ^ Health on the Net Foundation Mother and Child Glossary [1]
2. ^ G.B. v. Dearborn County Div. of Family and Children, 754 N.E.2d 1027 (Ind.Ct.App., 2001).
3. ^ James H Hutchinson Practical Paediatric Problems 4th ed. London: Lloyd-Luke 1975 p. 314 ISBN 0-85324-114-7
4. ^ Ali Hekmatnia Meconium Ileus [2]
5. ^ Peter G Jones Clinical Paediatric Surgery 2nd ed. Oxford: Blackwell 1976 pp 74-5 ISBN 0-632-00089-9
6. ^ Michael S Irish Surgical Aspects of Cystic Fibrosis and Meconium Ileus [3]

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