Fetal defaecation: Is it a normal physiological process?

Abstract

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.

The effect of mid-pregnancy shearing or yarding stress on ewe post-natal behaviour and the birth weight and post-natal behaviour of their lambs

“…Meconium staining of amniotic fluid is an indicator of fetal hypoxia at the time of delivery in humans (Kimble et al, 1999), but meconium coat staining has not been well characterised in sheep. In this study meconium coat staining between birth ranks and ewe treatments varied significantly.…”

Culture of Mouse Amniotic Fluid-Derived Cells on Irradiated STO Feeders Results in the Generation of Primitive Endoderm Cell Lines Capable of Self-Renewal in vitro

“…AF may therefore receive PrE endoderm progenitors through a transient communication between amniotic and yolk sacs via a transient neurenteric canal [Ozek et al, 2008]. Alternatively, XEN cell lines may derive from PrE derived cells in fetal gut [Kwon et al, 2008] which are then released into AF through regular emptying of fetal gut contents, an activity observed in both early and mid-gestation human fetuses [Kimble et al, 1999]. A less likely possibility is transdifferentiation of definitive endodermal progenitors into XEN cell lines when maintained under the culture conditions described above…”

Can placental histology establish the timing of meconium passage during labor?

“…Our observation that meconium was present in the majority of the placental tissues analysed within an interval as short as 10minutes is puzzling. It is likely that, despite clear amniotic fluid, meconium was already present in the macrophages when the membranes ruptured; such ‘old meconium’ had probably been passed before labor and had been cleared by the fetus itself through swallowing and by the placenta (18–23). In support of this, one study has shown a high incidence of meconium in the amniotic membranes of placentae from healthy term deliveries with clear amniotic fluid (24).…”