Dysfunctional Labor and Uterine Atony

Both dysfunctional labor and postpartum uterine atony are associated with conditions that can be expected to reduce myometrial oxygenation, and if obstruction of uterine venous return occurs in patients with these conditions, it could be expected to make already precarious myometrial perfusion even worse. Obesity, maternal short stature, and “uterine overdistention” are all conditions in which myometrial perfusion is already precarious. The myometrium of a large uterus is more vulnerable to hypoxia than that of a smaller uterus due to Laplace’s law, and this may explain the increased incidence of dysfunctional labor and postpartum uterine atony in patients with an “overdistended” uterus. None of these three pre-existing conditions can be “fixed.” They are intrinsic to a pregnancy. But what may be preventable—by the use of cardiac output-guided maternal positioning—is the positional component of decreased myometrial perfusion caused by obstruction of uterine venous return. This preventive therapy might reduce the incidence of both dysfunctional labor and postpartum uterine atony, which may be caused by myometrial hypoxia and acidosis in some patients.