Fetal defaecation: is it a normal physiological process?

It has been long known that the late gestation human fetus passes meconium in response to hypoxia. However, there is good evidence, from amniotic fluid studies measuring bile pigment and enteric enzyme content, to suggest that passage of meconium is a normal physiological event in the second trimester. Similarly there is some indirect evidence that fetal defaecation is a normal physiological process in the third trimester. However, this evidence is less strong, and it is safer to assume that in most cases meconium staining of liquor at this time is associated with fetal hypoxia. Dilation of the rectosigmoid portion of the distal bowel found in newborn infants with anorectal malformations supports the hypothesis that fetal colonic peristalsis and defaecation is a normal physiological process.