Patients with peripartum cardiomyopathy present with the typical signs and symptoms of left ventricular failure. The majority of cases occur after delivery and the immediate postpartum period. However, when the disease develops during the last month of pregnancy the diagnosis of cardiac failure is difficult to make by signs and symptoms alone since some of those symptoms, such as fatigue, orthopnea, and pedal edema, are common among normal parturients during late pregnancy. Further testing is required to establish the presence of cardiac failure. A chest x-ray consistently demonstrates cardiomegaly and pulmonary edema. Echocardiography confirms ventricular failure with increased left ventricular end-diastolic dimensions and decreased ejection fraction. Once cardiac failure is identified, peripartum cardiomyopathy must be differentiated from other disease processes that lead to heart failure, such as valvular heart disease.
That's the best I could do.
It is a rare deadly serious matter and survivors of Peripartim CM are advised to avoid future pregnancies.
This is a good read (Obstetrical Society, non-commercial site):