OBJECTIVE: Autoimmune-mediated congenital complete heart block (CCHB) is associated with significant perinatal morbidity and mortality, and prenatal monitoring of these fetuses is a significant challenge. The cerebroplacental Doppler ratio (CPR), defined as the ratio of the middle cerebral artery pulsatility index (MCA-PI) to the umbilical artery pulsatility index (UA-PI), is predictive of perinatal outcome in growth-restricted fetuses. This study tests the hypothesis that the CPR would be useful in monitoring fetal well-being in fetuses with CCHB. STUDY DESIGN: We reviewed data on all patients diagnosed prenatally with autoimmune-mediated CCHB at our institution over the past 2 years. The fetal echocardiograms from each patient were analyzed for: CPR, UA-PI, MCA-PI, cardiothoracic ratio, degree of tricuspid regurgitation, ventricular function and presence of effusions. We compared hemodynamic data from the fetal echocardiogram before delivery in patients who required urgent pacemaker placement postnatally to those patients that did not require an urgent pacemaker. RESULT: Five patients with autoimmune-mediated CCHB were identified, and two patients required urgent pacemaker placement. The CPR before delivery was significantly lower in the patients who required urgent pacemaker placement (0.97+/-0.06 versus 1.45+/-0.03; P=0.003), but there was no difference in other fetal echocardiographic markers between groups. Both patients requiring urgent pacemaker placement had a CPR less than 1.08. CONCLUSION: The CPR is predictive of postnatal outcome in fetuses with CCHB and is useful in prenatal monitoring of these patients.