[Intimate mechanism of premature separation of the normally inserted placenta].

Retro-placental haemorrhage comes from rupture of patent utero-placental arteries which are neither sclerosed nor thrombosed. This applies whether the form of haemorrhage is minor (simple depression found when the placenta is examined) or grave with utero-placental apoplexy (with complete detachment of the placenta and syndrome of shock). The method by which the arteries rupture depend on the intensity and excessive duration of uterine contractions: --moderate; normal uterine contractions give rise to a prolonged blockage of the return circulation, whereas the arterial flow has not stopped. Rupture occurs because the distended utero-placental arterial wall bursts under the insult of raised pressure during the uterine contraction; --intense; these anomalies come from total blockage, both veinous and arterial, and the arterial rupture is due to anoxaemic necrosis of the utero-placental arterial wall. The rupture of the utero-placental arterial wall, which is normally very fragile because it has no elasticity in its musculature, gives the explanation for the histogenesis of retro-placental haemorrhages.