REGULATION AND CONTROL OF THE

PASSAGE OF MECONIUM

Three theories are described:

1. The Mass Reflex Theory.
   Asphyxial stress is postulated to cause hypoxemia of the intrinsic muscle of the bowel and evoke an evacuation sequence by which the anal sphincter relaxes and the colonic muscles contract. There is no experimental evidence of any kind to support this theory. Peristalsis is actually suppressed in the presence of hypoxemia.
2. Vagal Stimulation.
   Intense vagal stimulation that can occur with cord compression produces increased vagal tone to the gut, initiating a variant of the gastrocolic reflex. There is no current experimental evidence to confirm or refute this theory.
3. Gut Maturation.
   The passage of meconium is a function of gut maturity i.e. gestational age and not as a direct result of spontaneous defecation. There is no association between the passage of meconium and underlying fetal disease. This is a common finding in some animal species such as the guinea pig.