Meconium is a thick, sticky, dark-greenish-black substance that is the earliest stool (bowel movement) of the newborn infant. It is composed of materials ingested during the time the infant spends in the uterus: intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. It is typically passed within 48 hours of birth. Meconium is composed of a variety of substances, including proteins, fats, carbohydrates, and minerals. It also contains sterols, which are steroid compounds that help the newborn body absorb fat-soluble vitamins. Additionally, meconium contains high levels of bilirubin, which is a breakdown product of red blood cells. The passage of meconium is an important event in the newborn period. Its passage indicates the newborn's maturity of the gastrointestinal tract and the normal functioning of the liver, pancreas, and gallbladder. It also serves as a marker of well-being, as the presence of meconium in the amniotic fluid can indicate fetal distress. Meconium can sometimes be difficult to pass due to its thick consistency. In these cases, the pediatrician may recommend the use of a laxative to help the infant pass the stool more easily. In more serious cases, a procedure known as meconium aspiration may be performed. This involves the suctioning of the meconium from the infant's lungs, and can prevent serious complications from developing. In conclusion, meconium is a thick, sticky substance that is the earliest stool of the newborn infant. It is composed of a variety of substances, including proteins, fats, carbohydrates, and minerals, and has important implications for the newborn's health. When it is difficult to pass, a laxative or meconium aspiration may be recommended by the pediatrician.