PRENATAL DIAGNOSIS Prenat Diagn 2010; 30: 395–401. Published online 16 March 2010 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/pd.2474 REVIEW Aortic isthmus Doppler velocimetry: role in assessment of preterm fetal growth restriction M. M. Kennelly 1,2 *, N. Farah 2 , M. J. Turner 2 and B. Stuart 1,2 1 Ultrasound and Fetal Medicine Centre, Coombe Women & Infants University Hospital, Dublin, Ireland 2 UCD Centre for Human Reproduction, Coombe Women & Infants University Hospital, Dublin, Ireland Intrauterine fetal growth restriction (IUGR) is an important pregnancy complication associated with significant adverse clinical outcome, stillbirth, perinatal morbidity and cerebral palsy. To date, no uniformly accepted management protocol of Doppler surveillance that reduces mortality and cognitive morbidity has emerged. Aortic isthmus (AoI) evaluation has been proposed as a potential monitoring tool for IUGR fetuses. In this review, the current knowledge of the relationship between AoI Doppler velocimetry and preterm fetal growth restriction is reviewed. Relevant technical aspects and reproducibility data are reviewed as we discuss AoI Doppler and its place within the existing repertoire of Doppler assessments in placental insufficiency. The AoI is a link between the right and left ventricles which perfuse the lower and upper body, respectively. The clinical use of AoI waveforms for monitoring fetal deterioration in IUGR has been limited, but preliminary work suggests that abnormal AoI impedance indices are an intermediate step between placental insufficiency- hypoxemia and cardiac decompensation. Further prospective studies correlating AoI indices with arterial and venous Doppler indices and perinatal outcome are required before encorporating this index into clinical practice. Copyright  2010 John Wiley & Sons, Ltd. KEY WORDS: aortic isthmus doppler; fetal monitoring; preterm fetal growth restriction; neurodevelopmental outcome INTRODUCTION Fetal growth restriction secondary to uteroplacental insufficiency affects up to 15% of pregnancies and is an important contributor to perinatal death, neonatal morbidity and long-term health problems (Barker et al., 1989; Pollack et al., 1992). It is a progressive vascular disorder associated with abnormal tertiary villous ves- sels which culminates in multi-vessel fetal hemodynamic abnormalities. In the absence of effective in utero thera- pies, timing of delivery becomes the critical management issue. The main aim of management is to deliver the fetus when the risks of in utero demise and irreversible end-organ dysfunctions associated with prolonging ges- tation are greater than the risks of preterm delivery. Longitudinal data have suggested a sequential pat- tern of hemodynamic changes, which form the basis for Doppler surveillance in intrauterine fetal growth restric- tion (IUGR) (Baschat et al., 2001; Hecher et al., 2001; Ferrazzi et al., 2002). Current ultrasound surveillance involves assessment of arterial (UA, umbilical artery; MCA, middle cerebral arteries) and venous Doppler waveforms to predict the critical point of change from adaptation to decompensation and in utero ischemic damage. The detection of a precursor step prior to decompensation could be used to improve current algo- rithms for the prediction and prevention of mortality *Correspondence to: M. M. Kennelly, UCD Centre for Human Reproduction, Coombe Women & Infants University Hospital, Dublin, Ireland. E-mail: mkennelly@doctors.org.uk and long-term neurodevelopmental deficits. To date, it is unclear whether ductus venosus (DV) Doppler is the most accurate Doppler for the detection of fetal decom- pensation. Some preliminary work suggests that abnor- mal aortic isthmus (AoI) impedance indices are an inter- mediate step between placental insufficiency-hypoxemia and cardiac decompensation, having important potential clinical applications (Figueras et al., 2009). Recent research has further advanced our understand- ing about the natural history of fetal vascular and behav- iorial adaptations to placental dysfunction. It is therefore timely to review our understanding of the pathologi- cal implications of abnormal UA waveforms and the sequence of Doppler changes prior to delivery. DISEASE PROGRESSION: SEQUENTIAL ARTERIAL AND VENOUS DOPPLER CHANGES In placental insufficiency, longitudinal studies have helped clarify the progression of fetal disease. Pla- cental vascular dysfunction results in elevated UA blood flow resistance which precedes the onset of growth delay. This triggers compensatory hemodynamic changes, which include blood flow redistribution toward essential fetal organs (brain, heart and adrenal glands) at the expense of other organ systems. Decreased resistance to blood flow is found in the MCA; this phenomenon is attributed to a ‘brain sparing’ adaptive response to fetal hypoxemia and is due to the auotoregulatory capabil- ity to vasodilate in the event of reduced perfusion. This Copyright  2010 John Wiley & Sons, Ltd. Received: 5 November 2009 Revised: 2 January 2010 Accepted: 7 January 2010 Published online: 16 March 2010