Color Doppler Imaging of Cerebral-Umbilical Pulsatility Ratio in Intrauterine Growth Retardation

Impaired fetoplacental perfusion is associated with intrauterine growth retardation.1 Pregnancy-related complications make a significant contribution to perinatal mortality and morbidity.2,3 Intrauterine growth retardation (IUGR) is defined as estimated fetal weight at <10th percentile or abdominal circumference <5th percentile irrespective of estimated fetal weight.1,4 Severe intrauterine growth retardation is defined as estimated fetal weight <5th percentile.5


Introduction
Impaired fetoplacental perfusion is associated with intrauterine growth retardation. 1Pregnancy-related complications make a significant contribution to perinatal mortality and morbidity. 2,3Intrauterine growth retardation (IUGR) is defined as estimated fetal weight at <10 th percentile or abdominal circumference <5 th percentile irrespective of estimated fetal weight. 1,4evere intrauterine growth retardation is defined as estimated fetal weight <5 th percentile. 5trauterine growth retardation is a syndrome characterized by failure of the fetus to reach its normal growth potential. 6It is the 2 nd leading cause of perinatal death and it is associated with significant morbidity including increased rates of meconium aspiration, hypoglycemia, respiratory distress syndrome, intrapartum asphyxia, developmental delay and still birth. 1,7trauterine growth retardation is associated with an increased risk of perinatal mortality and morbidity and impaired neurodevelopment. 8,9The correct detection of the compromised intrauterine growth retardation fetus to allow for timely intervention is a main objective of antenatal care. 10Umbillical artery and middle cerebral artery doppler velocimetry is the most rigorous evaluation test among the noninvasive tests of fetal well being. 11acental insufficiency, whether primary or secondary to maternal factors such as hypertension, poor nutrition etc, is the most common cause of intrauterine growth retardation which is an important obstetric problem on account of the high association perinatal mortality and morbidity. 1,2,12It is essential to recognize placental insufficiency early so that its hazards can be reduced.Doppler ultrasound enables a better understanding of the hemodynamic changes and has therefore become one of the most important clinical tools for fetomaternal surveillance in high risk pregnancies. 13ppler value was considered as normal when the cerebral-umbilical ratio was above 1.08 and below this the value was considered abnormal. 1,2,14Cerebralumbilical ratio remains constant in the last 10 weeks of pregnancy and therefore it is used (a single cutoff value of 1.08) for all the cases of 30−41 weeks of gestation. 15In intrauterine growth retardation, umbilical blood flow is significantly reduced, mainly due to change in the placental vascular resistance. 16 pregnancy with chronic fetal hypoxia, the blood volume in the fetal circulation is redistributed in favor of vitally important organs, i.e., the heart, kidney and brain. 17Vasodilatation of the middle cerebral artery with an increase in diastolic flow through it results in a decrease in its pulsatility index.The resulting hyperperfusion is considered pathological. 1,2,18e brain sparing effect is associated with an abnormal cerebral-umbilical ratio (<1.08). 19However, if hypoxia persists, the diastolic flow returns to the normal level.The cerebral-umbilical ratio remains constant during the last 10 weeks of gestation and provides better diagnostic accuracy than either vessels' pulsatility index (PI) alone. 1,20Doppler waveform abnormalities have been reported to be the most accurate predictor of poor neonatal outcome. 21Color Doppler apparatus may be used to assess the blood flow velocity profiles in the umbilical arteries to determine if complications associated with impaired trophoblastic invasion of the placental bed could be predicted by this measurement. 22On the basis of above facts "measurement of cerebral umbilical pulsatility ratio is a better predictor of small for gestational age fetuses".

Materials and Methods
This prospective study was done from January 2010 to September 2011 on 90 selected patients aged 17−35 years referred to the department of Radiology & Imaging.

Color Doppler scanning technique
All 90 patients were subjected to duplex Color Doppler examination, using 3.5 MHz transducer with 3 mm sample volume and medium filter.During the examination, the patient was in a semirecumbent position and the fetus was in quiet resting state.A Doppler beam was placed on the region of interest where the color flow was clearly noted and arterial pulsation was identified.
The flow velocity waveform was recorded from the umbilical artery (UA) and the fetal middle cerebral artery (MCA).After technically satisfactory Doppler waveform had been recorded, the PI of the umbilical artery and the MCA was noted and the ratio of the MCA and UA PI (the C/U ratio) was calculated.

Umbilical artery and middle cerebral artery PI
The formula of PI is (Peak systole−end diastole)/mean peak value.The cerebral-umbilical PI ratio remains constant in the last 10 weeks of the pregnancy and, therefore, a single cut-off value of 1.08 is considered normal.Below that value, velocimetry was considered abnormal. 1U ratio = MCA PI/UA PI; Normal: >1.08, Abnormal: <1.0

Results
All the subjects were divided into four age groups (Table I).The mean age of the subjects was 22.5 ± 9.8 years.The maximum 43.3% were within 21−25 year age group and minimum was within 16−20 year age group.Cerebro-umbilical (C/U) ratio remains constant in the last 10 weeks of pregnancy and so in this study a single cut-off value of 1.08 is considered for all cases of 30−41 weeks of gestation.Using the cut-off value study population was divided into normal and abnormal groups.
In pregnancies with chronic fetal hypoxia, the blood volume in the fetal circulation is redistributed in favor of vitally important organs, e.g.heart, kidneys and  The Color Doppler study of C/U vessels has made an advancement in new generation sonography equipment and expertise, which has brought a revolution in the field of diagnostic imaging to diagnose IUGR prenatally.This noninvasive imaging modality will be able to replace the other invasive diagnostic procedures.In this study using a C/U pulsatility ratio of less than 1.08, sensitivity was 94%, specificity 91.3%, positive predictive value 97%, negative predictive value 84% and diagnostic accuracy 93.4% for predicting adverse perinatal outcomes in IUGR.
In asymmetrical IUGR there is high umbilical artery PI and low middle cerebral artery PI.As a result, the C/U ratio is lower than normal growth retarded fetuses.
Different studies 1,2,10,22 have observed in their series that Doppler was significantly correlated with adverse perinatal outcomes where sensitivity ranged from 83−90% and specificity from 71−100%.Thus the parameters provide strong evidence that Doppler analysis is of great value in evaluation of prenatal diagnosis of fetuses at risk in IUGR.
The cerebral-umbilical PI ratio incorporates data of both placental status (umbilical artery) and fetal response (middle cerebral artery) in the prediction of adverse outcomes.
In this study, comparing the use of the C/U pulsatility index ratio, we found similar efficiency in the prediction of IUGR and adverse perinatal outcomes.This implies that perinatal centers can use this method in the evaluation of cases of IUGR.
Finally, color Doppler findings of cerebral-umbilical vessels and the validity tests in this study are almost identical as observed by other investigators.So, it can be concluded that Color Doppler evaluation of MCA and UA pulsatility ratio is an useful modality for diagnosis of IUGR.
age determined by birth weight measurement Discussion IUGR is a pathological condition which is strongly related to the development and function of the uteroplacental and fetoplacental circulation.An adequate fetal circulation is necessary for fetal growth.Umbilical artery (UA) velocimetry correlates with hemodynamic changes in the fetoplacental circulation.With an increase in the number of the tertiary stem villi and arterial channels as the fetoplacental compartment develops, the impedence in the UA decreases.A diastolic component in the UA flow velocity waveform appears during the early second trimester and progressively increases in the gestational age.A mature UA flow velocity waveform pattern shows low impedence and high diastolic flow with a low pulsatility index.During normal pregnancy, the MCA shows high resistance and low diastolic flow with an increase in the pulsatility index.

Fig 1 .Fig 3 .
Fig 1. Color Doppler of the umbilical artery showing a normal UA waveform pattern with low impedence, high diastolic flow and decreased pulsatility index Fig 3. Abnormal umbilical artery waveform patterns showing markedly reduced diastolic flow

Fig 4 .
Fig 4. Abnormal middle cerebral artery waveform pattern showing low resistance and high diastolic flow due to cerebral vasodilatation

Table I :
Age distribution of patients (n=90) Table V and Table VI).