Meconium is stool produced in the digestive system of a fetus. It is dark green and odorless. Before and during birth, the newborn excretes meconium, and it mixes with the amniotic fluid. In some cases, this process exposes the infant to meconium amniotic fluid fumes, causing meconium aspiration syndrome (MAS). MAS blocks the airways and reduces the surface area of the lungs, leading to depressed inhalation of oxygen.
During pregnancy, the fetus ingests materials through the umbilical cord that links him or her to the mother. Additionally, water, bile, amniotic fluid, and mucus enter the fetus’ digestive system. Studies show even lanugo, the soft hair on the fetus' skin, can get into the system. This mixture forms meconium.
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