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 flui d studies measuring bile pigment and enteric enzyme content, to suggest tha t passage of meconium is a normal physiological event in the second trimest er. Similarly there is some indirect evidence that fetal defaecation is a n ormal physiological process in the third trimester. However, this evidence is less strong, and it is safer to assume that in most cases meconium stain ing of liquor at this time is associated with fetal hypoxia. Dilation of th e rectosigmoid portion of the distal bowel found in newborn infants with an orectal malformations supports the hypothesis that fetal colonic peristalsi s and defaecation is a normal physiological process.