Editing Meconium aspiration syndrome (section)

=== Meconium passage as a result of foetal maturity ===
Although meconium is present in the [[gastrointestinal tract]] early in development, MSAF rarely occurs before 34 weeks [[gestation]].<ref name=":2" />

[[Peristalsis]] of the foetal intestines is present as early as 8 weeks gestation and the anal sphincter develops at about 20–22 weeks. The early control mechanisms of the anal sphincter are not well understood, however there is evidence that the foetus does defecate routinely into the [[amniotic cavity]] even in the absence of distress. The presence of fetal intestinal enzymes have been found in the amniotic fluid of women who are as early as 14–22 weeks pregnant. Thus, suggesting there is free passage of the intestinal contents into the amniotic fluid.<ref>{{Cite journal|last1=Poggi|first1=SH|last2=Ghidini|first2=A|date=2009|title=Pathophysiology of Meconium Passage into the Amniotic Fluid|journal=Early Human Development|volume=85|issue=10 |pages=607–610|doi=10.1016/j.earlhumdev.2009.09.011|pmid=19836908 }}</ref>

[[Motilin]] is found in higher concentrations in post-term than pre-term foetal gastrointestinal tracts. Similarly, intestinal parasympathetic innervation and [[myelination]] also increases in later gestations. Therefore, the increased incidence of MAS in post-term pregnancies may reflect the maturation and development of the peristalsis within the gastrointestinal tract in the newborn.<ref name=":2" />