Fetal cardiovascular magnetic resonance

Abstract

Since its initial inception in the early 1980s, the widespread use of ultrasound for imaging fetal cardiovascular anatomy and physiology has resulted in major improvements in our ability to treat fetal arrhythmia and diagnose congenital heart disease (CHD) prenatally. The result has been a reduction in fetal deaths attributable to supraventricular tachycardia and complete heart block, improvements in perinatal outcomes in pregnancies affected by CHD, and the option of termination of pregnancy in the setting of serious cardiac and associated congenital malformations [10]. In recent years, we have learned how the natural history of severe forms of CHD may be modified with minimally invasive in utero surgical procedures, a development that is entirely attributable to the development of fetal echocardiography. Doppler ultrasound has also improved the detection and management of intrauterine growth restriction (IUGR) through the identification of the changes in fetal cerebral, peripheral, and placental vascular resistances that occur in response to acute fetal hypoxia [7, 56]. However, while Doppler aids in the detection of fetal hypoxia by identifying fetal circulatory adaptations to placental insufficiency, one drawback of the modality is that it does not provide any direct information about fetal oxygenation. Furthermore, animal studies suggest that chronic fetal hypoxia is associated with a reduction in fetal oxygen consumption (VO2) and normalization of blood flow distribution, resulting in potentially falsely reassuring findings on Doppler ultrasound [34, 39, 42]. By contrast, MRI offers the potential to directly quantify the oxygen content of fetal blood and may therefore provide more sensitive measures of chronic placental insufficiency [60, 61]. Fetal cardiovascular MRI may also be helpful as an adjunct to conventional ultrasound assessment in the setting of CHD. The abnormal cardiac connections and obstructions of flow that characterize CHD have long been suspected of disrupting oxygen transport across the fetal circulation, and MRI has provided a new way to examine the relationships between fetal hemodynamics and organ growth and development [52].