In addition, their cardiac reserve, or the amount of blood that the heart can pump per minute with exercise, is somewhat limited. Thus, some of these women may not have the cardiac reserve to support pregnancy. The inability to increase cardiac output appropriately may be the reason for the high frequency of spontaneous abortion or miscarriage. The fetus may not be getting enough blood supply. Furthermore, I believe it is well known that patients who have had the Fontan operation have problems with fluid after the operation.
Many patients have to take diuretics long-term after the operation.
Thus, it seems reasonable to assume that increasing blood volume by a significant amount would create problems with the Fontan circulation. Canobbio's study evaluated only 33 pregnancies in 21 women and only 15 went to term. This is a rather small sample to make broad statements from. Although these data are promising, the ultimate answer remains to come forward. Echocardiography Q .