Pathogenesis: reduced oxygen saturation and vaso-occlusion, with or without complicating factors (toxemia, infection, smoking, drug use, etc)
The fetus may show growth restriction.
The placental weight may be small (with multiple infarcts), normal or increased (with diffuse edema or congestion) for gestational age.
Histologic changes in the placenta:
(1) infarcts of villi (microscopic or macroscopic)
(2) Tenney-Parker changes (increased syncytial knots)
(3) villous edema
(4) increased fibrin deposition
(5) fibrosis of villi
(6) abruption
(7) sickle-shaped red blood cells in the intervillous space
(8) microcalcifications
The more severe the changes the more likely that the infant will be adversely affected.
