Role of imaging in diagnosis and evaluation of intrauterine growth restriction

IUGR(Intrauterine growth restriction) is one of the important causes of perinatal mortality and morbidity. IUGR refers to any process that is capable of limiting intrinsic fetal growth potential "in utero". A fetus is growth restricted if its weight is below the 10(th) percentile for gestational age, due to a pathologic process. Most cases of growth restriction are caused by placental insufficiency. IUGR may also result from a chromosomal anomaly or intrauterine infection. IUGR fetuses have a four-to eightfold increased risk of perinatal mortality, thus antenatal diagnosis of IUGR is of great value. Sonographic diagnosis of IUGR can be achieved by the straightforward approach of sonographic calculation of estimated fetal weight, which falls below the 10(th) percentile for the gestational age in IUGR fetuses. However, the accuracy of this approach is limited. Other sonographic criteria for diagnosing IUGR are elevated HC/AC ratio, elevated FL/AC ratio, presence of oligohydramnios without ruptured membranes, and presence of advanced placental grade. Doppler imaging has an important role in diagnosis and estimation of severity of IUGR. Umbilical artery(UA) shows a decrease in end-diastolic flow velocity which may even reverse and Middle cerebral artery (MCA) may show lower pulsatility index(PI)due to central redistribution in IUGR fetuses. UA/MCA Doppler ratio is another parameter believed by some authors to be more accurate in the prediction of adverse perinatal outcome than UA Doppler indices alone. Thoracic Aorta may show reduced, absent or reversed diastolic flow in IUGR fetuses. Progressive worsening is manifested by absent diastolic flow followed by reversal of diastolic flow in both Aorta and umbilical artery. Abnormal fetal. venous flow velocity waveforms in IUGR are:1- An increased a wave coupled with a decreased diastolic forward peak in Inferior Vena Cava (IVC),2- Lack of continuous forward flow in ductus venosus,3- A pulsatile umbilical vein. In some studies abnormal Doppler velocimetry of ductus venosus was found to be the significant parameter associated with perinatal death and low 5-min Apgar scores. Magnetic Resonance Imaging(MRI) has been used recently to detect IUGR. By using perfusion-sensitive echoplanar imaging, maps of placental perfusion can be created, which enable early detection of IUGR. MRI also can be used to calculate fetal weight, which is believed by some authors to be better than sonographic estimates. No single criterion pernits diagnosis of IUGR, so clinical and imaging findings should be combined for a correct diagnosis and proper management.