Presented by Dr. Sandeep Garg (Resident)Department of Radiodiagnosis CMS 3rd Nov, 2011
25 yrs female with 30 wks of POG and uncontrolled hypertension was referred from gynae/obsc dept for doppler. USG and doppler findings include ◦ >HC/AC ratio 1.32 ◦ Severe oligohydraminos (AFI 3 cm) ◦ MCA PI 1.27 ◦ UA PI 1.39 ◦ MCA/UA PI ratio – 0.91 Impression: fetal hypoxia/ IUGR
IUGR: fetus with birth weight <10th percentile for gestational age due to pathologic process. SGA: fetus with birth weight <10th percentile for gestational age in the absence of pathologic process
Symmetrical : Uniformly small, HC:AC,FL:AC-Normal seen in chromosomal anomalies Asymmetrical : fetal abdomen is disproportionately small (Head sparing effect) HC>AC HC:AC, FL:AC-Elevated
elevated HC/AC ratio (positive predictive value 62%) elevated ratio of femur length to abdominal circumference (FL/AC) presence of oligohydramnios without ruptured membranes presence of advanced placental grade (Grannum grade 3)
Typically, scores of 6 or below are considered frankly abnormal, and scores of 7 and 8 are considered suspicious. Reduced biophysical profile scores are found in growth restricted pregnancies that already demonstrate abnormal umbilical and fetal Doppler findings.
Most of these fetuses are constitutionally small, and are not suffering from uteroplacental insufficiency. An inter-twin growth discrepancy of 20–25% is considered to be significant. Twin-to-twin transfusion syndrome (TTTS)- Color Doppler findings in the donor are usually typical of uteroplacental insufficiency
Quantitative analysis ◦ Pulsatility index (PI) ◦ Resistance index (RI) ◦ Systolic/diastolic ratio Qualitative analysis ◦ Uterine artery: presence or absence of early diastolic notch ◦ UA : normal, with reduced diastolic flow, absent EDF, reversed EDF
Uterine arteries branch into arcuate arteries, leading to spiral arteries within myometrium. With advancing pregnancy, due to trophoblastic invasion of uterine spiral arteries, it dilates and result in fall in resistance to blood flow. Uterine blood flow in non pregnant women is 50 ml/min and increase to over 700 ml/min in 3rd trimester. Hence, in normal pregnancy diastolic component is transformed from one of low peak flow velocity and early diastolic notch , to one of high flow and no diastolic notch by 18 to 22 wks, PI value <1.2 PI >1.45 with bilateral notches (abnormal) is s/o clinically significant uteroplacental vascular ischaemia.
Characteristic umbilical artery waveforms have also been correlated to various degrees of fetal hypoxemia and acidemia. Absent end-diastolic frequencies ◦ 75% of the placental vascular bed has been obliterated ◦ 85% chance that the fetus will be hypoxemic and a 50% chance that it will also be acidemic. Reversed end-diastolic frequencies ◦ ten-fold increase in perinatal mortality
Fetal arterial waveforms are acquired from the thoracic aorta and middle cerebral arteries. With fetal hypoxemia, there is conservation (or increase) of blood flow to the fetal brain, heart and adrenal glands with concomitant decrease in flow to the splanchnic bed and extremities. This phenomenon is termed ‘arterial redistribution of blood flow’, and serves to deliver oxygen and nutrients to vital organs in the face of impaired placental function. Hence, fetal arterial Dopplers can be used to monitor fetal compensatory responses to progressively deteriorating placental function.
MCA can be easily demonstrated by color doppler in transverese fetal head position. At 28-32 wks, MCA is characterized by high systolic velocities and minimal diastolic velocities, resulting in high PI values (>1.45). In fetal hypoxia, vascular tone is increased in MCA resulting in increased diastolic velocity and reduced PI values.
NormalWith hypoxia there is cerebralvasodilatation, so initially thediastolic flow may be in thenormal range ,when thevasodilatation ability isexhausted as with fetalacidosis the resistance startsincreasing again.
A longitudinal view of the fetal thoracic aorta is obtained with color flow imaging. The pulsed Doppler sample gate should be placed on the linear portion of the descending thoracic aorta, above the level of the diaphragm
The ductus venosus is the main vessel through which oxygenated blood returning from the placenta is directed to the fetal heart and circulation. With worsening fetal hypoxemia, abnormal umbilical artery waveforms and severe fetal arterial redistribution develop. In addition, there is also increased redistribution of highly oxygenated umbilical vein blood through the ductus venosus to the fetal heart. When the fetal condition becomes critical, abnormal ductus venosus flow waveforms are seen.
Biometry ◦ EFW 640 g (<10th centile) ◦ HC/AC ratio 1.35 (normal <1.2) ◦ AFI 7 cm (normal 10-20 cm) Doppler ◦ Uterine arteries- B/L early diastolic notch ◦ Lt uterine artery PI 1.97, Rt PI 1.65 ◦ UA- absent EDF in both ◦ Smooth umbilical venous cord flow, peak vel 16cm/sec ◦ MCA- PI 1.12 (redistribution) ◦ Ductus venosus – positive A wave 32 cm/sec (normal) Biophysical profile score- 8/8 normal Anatomic evaluation- short femurs, mildly echogenic bowel
Gramellini et al (1992) studied that in 30-41 wks POG, MCA/UA PI ratio (cerebro-umbilical flow) <1.08 is better predictor of fetal insufficiency than MCA PI or UA PI alone. Diagnostic accuracy for the cerebral- umbilical ratio was 90%, compared with 78.8% for the middle cerebral artery and 83.3% for the umbilical artery.
1990 G.Mari proposed the use of MCA dopplers for the diagnosis of anemia The sensitivity of the peak systolic velocity for the prediction of moderate anemia and severe anemia in the fetuses without hydrops was 100 percent , with a false positive rate of 12 percent. The positive and negative predictive values were 65 percent and 100 percent, respectively.
The risk of anemia was high in fetuses with a peak systolic velocity of 1.50 times the median or higher. Fetuses with values below 1.50 either did not have anemia or had only mild anemia.
the MCA PSV is effective for accurate diagnosis of fetal anemia and can avoid about 70% of invasive procedures.