The mechanism of midtrimester abortion induced by intra-amniotic instillation of hypertonic saline: a modification of Gustavii's lysosomal hypothesis.

This modification of Gustavii's hypothesis recognizes the central role of saline-induced decidual cell necrosis and secondary prostaglandin release in the initiation of myometrial activity. In the absence of significant necrosis in the decidua basalis, passive stretching of the subplacental myometrium is considered to activate this region leading to secondary intervillous stasis and the reduction in progesterone delivery to the myometrium and systemic circulation. This drop in progesterone further sensitizes the myometrium to PGF2alpha stimulation and helps the self-sustaining process of myometrial activity culminating in clinical abortion. A third hypothetical contributing factor may be the loss of some myometrial inhibitor normally present in the amniotic fluid.