Interpretation of waveforms:

Interpretation of waveforms:

1. A SGA fetus with normal umbilical artery wave forms will not develop loss of end diastolic frequencies within a seven day period, so that monitoring can be performed weekly.

2. The finding of a symmetrical small fetus with absent end diastolic velocities in the umbilical artery but with normal utero placental waveforms suggest the possibility of a primary fetal cause for growth retardation such as chromosomal abnormality or a TORCH virus infection.

3. Fetus demonstrating absence of end diastolic velocities but are managed along the standard clinical have a 4O% chance of drying and atleast a 25% morbidity rate from necrotizing enterocolitis, hemorrhage or coagulation failure after birth.

4. The time between loss of end diastolic velocity and fetal death appears to differ for each fetus.

5. Loss of end diastolic velocities precedes changes in the non- stress test by some 7 to 42 days in fetuses shown to be SGA on real time ultrasound. Many centers monitor SGA fetuses solely with Doppler ultrasound.
6. Reverse end diastolic velocities are associated with 85% chance that the fetus will be hypodc In utero and 50% that It will be addotlc.

7. 10% of fetuses demonstrated to be asymmetrically small for gestation age on real time ultrasound will demonstrate loss of end diastolic velocities.

8. Usually second twin of monochorlonic twins shows changes of IUGR. Difference In the systoic/ diastolic ratio of more than 0.4 between twins suggests that the second twin Is having IUGR.

          In twin pregnancies with discordant growth patterns, Doppler analysis of the umbilical arteries appears to be an useful adjunct to serial growth measurements, allowing recognition of high risk twin pregnancies which require more Intense surveillance.

          In twin-to-twin transfusion syndrome, the shared circulation has the result that Doppler waveforms in the umbilical arteries of both twins are similar (Faber R Viewhweg B & Burkhadt u 1995).

          If both the Doppler systolic to diastolic ratio of umbilical artery and the antepartum testing are abnormal, there is a significantly increased incidence of IUGR (47%), fetal distress necessitating cesarean section (67%) and admission to neonatal Intensive care units (86%). (Curtis Lowery JR 1990).

MIDDLE CEREBRAL ARTERY

          The fetal cerebral blood flow is a high Impedance low flow circulation. it is a more sensitive parameter of fetal oxygenation status than umbilical blood flow. With color Doppler technology it is now possible to investigate the main cerebral arteries and to evaluate vascular resistance of the same (Arbelile et al.,1990).

          In response to prolonged fetal hypodc stress, circulatory adaptation occurs, resulting In redistribution of the cardiac output to provide constant oxygen supply to brain and other essential organs like heart and adrenal glands (Peeters et al.,1979).

Cerebral Doppler Indices:

          To quantify the vascular resIstance, the indices used are the same as that of uterine and umbilical arteries.

1. Pulsatillty Index (PI).
2. Systolic/ Diastolic (S/D) ratio.
3. ResIstance index (RI):

          In normal fetuses, there Is little diastolic flow in middle cerebral artery and the systdlc/ diastolic ratio Is normally more than 4 throughout the regnancy. The diastolic flow velocity increases slightly during gestatIon, resulting In some diminution of systollcl diastolic ratio as a function of gestatlonal age (Peter J Callen 1995). The mean PI in middle cerebral artery at 28 weeks of gestation is 1.6±0.4OA and at 40 weeks It Is 1.2±0.4 with a significant reduction after 32 weeks of gestation. This fall In PI suggests a change in cerebrovascular resistance as a result of hemodynamic redistribution favouring blood supply to the brain during the last eight weeks of gestation (Judy W Wladimiroof 1991).

          There is redistribution of fetal blood flow In response to hypoxia with a selective Increase in the blood flow to the brain, heart, adrenal glands at the expense of viscera. This reduction reflects the morphological findings in IUGR, with the head continuing to grow at the expense of a relatively smaller abdomen.

          Fetal outcome is thought to be related both to the severity and duration of hypoxia, as well as the gestation age at delivery. It is assumed that hypoxia will tend to increase with Increasing gestation age in fetuses with growth retardation and that this will lead to a greater redistribution of blood flow.

          The fetus with significant reduction of umbilical flow should have dilated cerebral flow. If it does not, it is critically ill or not hypoxic. If it is not hypoxlc, It may have congenital heart disease, and the reduced peripheral flow is caused by reduced forward flow, not increased resistance.

          Abnormal cerebral (MCA)/ umbilical artery pulsatility ratio help in distinguishing small distressed fetuses from the small relatively healthy ones (Arduini and Rlzzo 1992). Normally the ratio of Pt of MCA/ umbilical artery is 2:1. If It Is one It indicates IUGR. (Rowlands Di & Fernando Arias 1995) SGA fetuses with an abnormal umbilical artery PI have cerebellar sparing effect as their PI was less than normal. (Verparojkit B 1998).

          Doppler flow measurement of MCA provides useful information about perinatal outcome, especially in the high risk pregnancies (Atlas C 1996).

          In suspected IUGR, while an abnormal umbilical artery PI is a better predictor of adverse perinatal outcome, than an abnormal MCA or renal artery PI. A normal PI of MCA may help to identify fetuses without major adverse perinatal outcome, especially before 32 weeks of gestation (Katherine W Fong 1999)

Cerebro-Placental Ratios (CPRs):

          It is a comparison of cerebral resistance with that of umbilical resistance. Since the cerebral vascular resistance remains higher than placental resistance, the CPR is >1.

          The CPR is a better predictor of small for gestational age newborns, and adverse perinatal outcome, then either the middle cerebral artery or umbilical artery alone (Gramellini et al, 1992).

Clinical diagnosis of IUGR:

          Ultrasound is the best investigation to evaluate fetus starting from conception till delivery in providing extensive information.

          In first trimester accurate knowledge of menstrual age is critically important in diagnosing IUGR since some forms of IUGR affect crown rump length in the first trimester of pregnancy like aneu ploidy.

          In second trimester, biparietal diameter, head circumference, abdominal circumference and femur length provide a wealth of information about head size, trunk size, soft tissue mass, weight, length and body proportionality.

1. Head size: It is determined by measuring BPD and HC. A head circumference below 3rd percentile for age is the cause of concern for symmetrical IUGR where head size is compromised early in pregnancy.

2. Trunk size: It is determined by abdominal circumference. Abdominal circumference is the most sensitive single indicator of IUGR of the both symmetrical and asymmetrical types. AC measuring below 10th percentile for gestation age is highly suspicious of IUGR. The rate of growth of abdominal circumference also acts as a parameter to detect IUGR. An abdominal circumference growth of less than 1 cm in 14 days is indicatve of IUGR.

3. Fetal length: This is determined by femur length and crown heel length. Crown heel length is important in measuring ponderal index.

4. Body proportionality:
1. Head circumference/ abdominal circumference (HC/AC) is dependent on menstrual age and can detect about 2/3”’ cases of asymmetric IUGR.
2. Femur length! abdominal circumference (FL/AC) is much more useful. This remains constant after 20 weeks. The normal value is 22±2.
3. Fetal ponderal index: it is gestation age dependent and has a constant value throughout the second half of pregnancy. The normal value of fetal ponderal index is 8.325±2.5. A fetal ponderal index of 7 or less is strongly suggestive of fetal malnutrition.

5. Intrauterine environment The signs of IUGR are:
1. Oligohydramnios: It Is associated with UJGR. Largest single liquor pocket of less than 1. an In Its- greatest vertical dimension and Intact membranes with no fetal renal abnormalities Is an Indirect sign of Intrauterine growth retardation.
2. Grade 3 placenta before 36 weeks of gestation with ret weight less than 2700 g.
3. Delayed appearance of distal epiphysis after 32-33 weeks.

          Sometimes ultrasound cannot detect IUGR and the fetus developing distress in high pregnancies. In these cases and other related complicated pregnancies including maternal diabetes mellitus where fetal distress is expected, Dopk, evaluation is found to be highly sensitive. With the help of color Doppler, the identification of vessels which are evaluated for Doppler study can become simple.