THE ROLE OF COLOR DOPPLER ULTRASOUND

IN ANTEPARTUM SURVEILLANCE

(DR BHARTI GAHTORI)

The purpose of obstetric care is to optimize maternal and fetal safetyThe aim of fetal surveillance is to-- Reduce the incidence of fetal death through detection of hypoxic or acidemic infant .- Minimise the morbidity by optimizing the timing of delivery- Identify the fetus that are genuinely at risk of chronic hypoxia and avoid unnecessary intervention in those that are not .- Identify those fetus that are at greater risk of acute hypoxia in labour-To act as screening as well diagnostic modality to detect the influence of maternal, placenta & fetal factor on the fetus and guide regarding frequency of follow up & timely intervention.

ANTEPARTUM FETAL SURVEILLANCE

WHO ARE THE NEEDY ONESMATERNAL AND/OR FETAL CONDITIONS AT RISK OF CHRONIC HYPOXIA ARE-COMMON MATERNAL INDICATIONS:-Hypertensive disorders of pregnancy-Chronic renal disease-Maternal diabetes-Antiphospholipid syndrome and related autoimmune disease-Cyanotic heart disease

COMMON FETAL INDICATIONS:-Intrauterine growth restriction (IUGR)-Reduced fetal movement-Post date pregnancy-H/o previous IUD , still birth , IUGR , oligohydramnios -Raised serum alpha protein

METHODS OF ANTENATAL FETAL SURVEILLANCE

1) Fetal Movement Counting2) Non-Stress Test 3) Contraction Stress Test 4) Sonographic Assessment of Fetal Behaviour and/or5) Amniotic Fluid Volume6) Arterial and venous doppler - Uterine Artery Doppler - Umbilical Artery Doppler - Other adjuvant Doppler Parameters including

MCA , Ductus venosus , IVC , thoracic aorta , Umbilical vein et al

Doppler ultrasonography is a non-invasive procedure that uses detectable changes in high frequency sound waves (2-20 MHz), based on the Doppler effect, to create clear digital images in real time. Doppler ultrasonography is based on two basic principles:1. Ultrasound principle:High-frequency sound wave aimed at a stationary target will be reflected back and detected. The machine then displays the distances and intensities of the echoes on the screen, forming a two dimensional image2. Doppler principleEchoes from moving target exhibit slight differences in the time for the signal to be returned to the receiver . It brings changes in the sound pitch depending on the movement of the object ( blood) in relation to the detector (positive or negative shift)- the speed of sound in blood is 1570 m/s)

DOPPLER ULTRASOUND

When the frequency of sound emitted from a stationary source is fixed, and its insonation angle is known, the Doppler shift (i.e. the difference between the emitted and the reflecting frequency) f D = 2f0v cosθ/c where f D = Doppler shift, f0 = frequency of the transmitted beam, v = velocity of sound within the tissue, θ = insonation angle &c = speed of sound in tissue

:.

PRINCIPLES OF DOPPLER SHIFT

1.Continuous wave Doppler ultrasoundContinuous emissions from transducer, enabling the measurement of high velocity blood flow and reception of sound. E.g Umbilical Artery signals returning from the insonated tissues overlap and are not distinguished as separate entities vessel the signal is coming from. Not useful for small vessels.

2.Pulsed wave dopplerPW emits pulses of sound only for a fraction of time and receives the returning signals the rest of the time. Each returning echo is recognized by its timing and thus the system defines the depth of the structure . As it is gray scale, imaging of small and tortuous vessels is extremely inaccurate.

3.Duplex Doppler ultrasoundCombination of previous two types, in order to allow accurate anatomical location of studies blood flow. Good for assessing small and tortuous vessels

TYPES OF DOPPLER ULTRASOUNDS

4. Color Flow Imaging Color Doppler Imaging (CDI)#  Here color-coded pulsed Doppler information is superimposed on the B- mode ultrasonic image. # Color is assigned to flow direction. Stationary structures are presented in basic gray-scale image. #The color saturation is related to the magnitude of the frequency shift .#Color flow imaging facilitates the detection of small vessels and slow blood-flow velocity. #The CDI rely on mean velocity of the blood flow ,so uses impedance indices (RI/PI) . Color Doppler Energy (CDE) #It detects the energy of Doppler signals generated from moving blood. #CDE is able to display lower volumes and velocities. It enable the investigation of blood flow with very low velocity, even in the vessels running at 90 degrees to the insonation angle of the ultrasound beam . #CDE is not affected by aliasing like CDI#The conventional semi quantitative analysis based on the use of impedance indices (RI/PI )is not applicable to CDE studies since it measures the amplitude of signal.

The size of the Doppler signal is dependent on:

(1) Blood velocity: As velocity increases, so does the Doppler frequency. Increase in viscosity has opposite effect.(2) Ultrasound frequency: Higher ultrasound frequencies give increased Doppler frequency. As in B-mode, lower ultrasound frequencies have better penetration. The choice of frequency is a compromise between better sensitivity to flow or better penetration.(3) The angle of insonation: The Doppler frequency increases as the Doppler ultrasound beam becomes more aligned to the flow direction (the angle θ between the beam and the direction of flow becomes smaller).(4) Aliasing:(5) Type of machine used(6) Expertise of the Ultrasonologist

A: Higher-frequency Doppler signal (beam aligned to the direction of )B: Less aligned than A and produces lower-frequency Doppler signalC: The beam/flow angle is almost 90°and there is a very poor Doppler signalD: The flow is away from the beam and there is a negative signal

STRUCTURE OF PLACENTA

The conversion of the spiral arteries to uteroplacental arteries is termed a physiological change . Spiral arteries becomes dilated and tortuous.The diameter increases from 15–20 to 300–500 mm, due to the invasion of cytotrophoblast cell which leads to a complete absence of muscular and elastic tissue, no continuous endothelial lining, mural thrombi and fibrinoid deposition It reduces the impedance to flow and creates high-flow, low-resistance placental circulation and optimizing fetomaternal exchange in the intervillous space. This modification permit the ten-fold increase in uterine blood flow which is necessary to meet the respiratory and nutritional requirements of the fetus and placenta

It occur in two stages: the first wave of trophoblastic invasion converts the decidual segments of the spiral arteries in the first trimester and the second wave converts the myometrial segments in the second trimester .

PLACENTA - A UNIQUE ORGAN

(1) Resistance index (RI) (also called resistive index or Pourcelot’s index)(2) Systolic/diastolic (S/D) ratio, also called the A/B ratio(3) Pulsatility index (PI)All are angle independent ratios

All three indices were found to correlate well with the actual impedance to flow. :1. When diastolic flow increases the S/D ratio decreases.

2. When end diastolic velocity is absent (zero), the S/D ratio becomes infinite.

3. The lower the diastolic velocity in the S/D ratio the larger the systematic error.

4. In cases with absent or reverse diastolic flow velocity only the PI can provide us with a measurable entity for future reference.

DOPPLER INDICES

UTERINE ARTERY DOPPLERUterine artery Doppler provides flow resistance

information on the maternal surface of the placenta( maternal-placental unit) and therefore reflects the adequacy of trophoblastic invasion and spiral artery conversion. In normal pregnancy the S/D ratio or RI values significantly decrease with advancing gestation until 24 to 26 weeks.

UTERINE ARTERY SAMPLING SITE

First-trimester uterine artery evaluation (Figure 1)1. Transabdominal technique• Transabdominally, a midsagittal section of the uterus is obtained and the cervical canal is identified. The probe is then moved laterally until the paracervical vascular plexus is seen. Color Doppler is turned on and the uterine artery is identified as it turns cranially to make its ascent to the uterine body..2. Transvaginal technique contd…..

Second-trimester uterine artery evaluation 1. Transabdominal technique• Transabdominally, the probe is placed longitudinally in the lower lateral quadrant of the abdomen, angled medially. Color flow mapping is useful to identify the uterine artery as it is seen crossing the external iliac artery.• The sample volume is placed 1 cm downstream from this crossover point.• In a small proportion of cases if the uterine artery branches before the intersection of the external iliac artery, the sample volume should be placed on the artery just before the uterine artery bifurcation.• The same process is repeated for the contralateral uterineartery.• With advancing gestational age, the uterus usuallyundergoes dextrorotation. Thus, the left uterine arterydoes not run as lateral as does the right.

Normal impedance to flow in the uterine arteries in 1º trimester

Normal impedance to flow in the uterine arteries in early 2ºtrimester

Normal impedance to flow in the uterine arteries in late 2º and 3º trimester

Normal Pregnancy - Uterine artery waveform

Normal impedance to flow in the uterine arteries (with the characteristic waveform of early diastolic notching)

Increased impedance to flow in the uterine arteries (with the characteristic waveform of early diastolic notching)

Very high resistance to flow in the uterine arteries (with reversediastolic flow)

ABNORMAL UTERINE A. DOPPLER WAVEFORM

There is an association between high resistance uterine artery Doppler at the end of first trimester (11-14 weeks) and in mid-trimester, with the subsequent development of early-onset fetal growth restriction, pre-eclampsia and abruption. This is being used by various centres as screening modality in High risk cases.

Uterine artery Doppler was considered abnormal between 19 and 23 weeks’ gestation if -# Resistance index( RI) greater than the 95th centile# Early diastolic notch in either of the two uterine arteries)# When the mean PI of both uterine arteries was

greater than (1.45 – 1.58)

Predictive value of Uterine A. doppler findings

UTERINE ARTERY DOPPLER ( RCOG guidelines )

#In a low risk population 2nd trimester has limited accuracy to predict a SGA.#In high risk populations Doppler at 20–24 weeks of pregnancy has a moderate predictive value for a severely SGA neonate.#In women with an abnormal UA Doppler at 20–24 weeks of pregnancy, subsequent normalisation of flow velocity indices is still associated with an increased risk of a SGA neonate.#Women with an abnormal UA Doppler at 20–24 weeks (defined as a pulsatility index [PI] > 95th centile) and/or notching should be referred for serial ultrasound measurement of fetal size, AFI , BPP with umbilical artery Doppler commencing at 26–28 weeks of pregnancy.#Women with a normal uterine artery Doppler should be offered a single scan for fetal size and umbilical artery Doppler during the 3rd trimester.

UMBILICAL ARTERY DOPPLER- Umbilical Artery Doppler is essentially placental, rather than fetal Doppler, providing information on the fetal side of the placenta.- Flow velocity measurements performed at this level represent downstream resistance, namely those at placental stem and terminal villi

UMBILICAL ARTERY SAMPLING

It is easy to sample , Best site is near its origin from the placenta . Here it gives better representation of downstream impedence ( i.e Placenta )

NORMAL PREGNANCY - UMBILICAL A. WAVEFORM Normal impedance to flow in the

umbilical arteries and normal pattern of pulsatility at the umbilical vein in 1º trimester

Normal impedance to flow in the umbilical arteries and umbilical vein in early 2ºtrimester

Normal impedance to flow in the umbilical arteries and umbilical vein in late 2º and 3º trimester

CHARACTERISTICS OF UMBILICAL ARTERY WAVEFORM & INDICES• The Umb arterial waveform usually has a “Saw tooth" type pattern with flow always in the forward direction.

•The S/D ratio decreases, from about 4.0 at 20 weeks to 2.0 at term. The S/D ratio is generally less than 3.0 after 30 weeks

•Umb A. Doppler may be a useful adjunct in the management of pregnancies complicated by FGR

•No role in screening of low-risk pregnancies or for complications other than growth restriction

PREDICTIVE VALUE OF UMBILICAL A. WAVEFORM AND INDICES# If impedance is increased in Umb A > 60% of the placental vascular bed is obliterated

# AEDF and REDF have an associated 40% and 70% perinatal mortality, respectively8.

# AEDF in Umb A and MCA PI < 5th percentile are considered "early" stage changes of IUGR.

# REDF in the Umb A, along with pulsation in Umb Vein are the best predictor of severe fetal distress, so termination of pregnancy must be considered as soon as possible.

- High pulsatility index

- Very high pulsatility index

Umbilical arteries (AEDV)- Very high pulsatility index.- End diastolic velocity- Pulsation in the umbilical vein

Umbilical arteries(REDV)- Severe cases absence of reversal of end diastolic frequencies

ABNORMAL UMBILICAL A. DOPPLER WAVEFORM

ABNORMAL: •If the S/D ratio is above the 95th percentile for gestational age. •In extreme cases of growth restriction, end-diastolic flow may become absent or even reversed •These are ominous findings and should prompt a complete fetal evaluation—almost half of cases are due to fetal aneuploidy or a major anomaly •In the absence of a reversible maternal complication or a fetal anomaly, reversed end-diastolic flow suggests severe fetal circulatory compromise and usually prompts immediate delivery

UMBILICAL ARTERY DOPPLER (RCOG guidelines)

#In a high–risk population, the use of umbilical artery Doppler has been shown to reduce perinatal morbidity and mortality. Umbilical artery Doppler should be the primary surveillance tool in the SGA fetus.#When umbilical artery Doppler flow indices are normal it is reasonable to repeat surveillance every 14 days.#More frequent Doppler surveillance may be appropriate in a severely SGA infant.#When umbilical artery Doppler flow indices are abnormal (pulsatility or resistance index > +2 SDs above mean for gestational age) and delivery is not indicated repeat surveillance twice weekly in fetuses with end–diastolic velocities present and daily in fetuses with absent/reversed end–diastolic frequencies.

The middle cerebral artery is the most studiedcerebral artery because (a) it is easy to sample(b) it provides information on the cerebral blood flow in normal and IUGR fetuses and (c) it can be sampled at an angle of 0° betweenthe ultrasound beam and the direction of the blood flow.Therefore, for the middle cerebral artery we are able to determine angle-independent indices (the most used is the pulsatility index) and also the real velocity of blood flow.

MIDDLE CEREBRAL ARTERY DOPPLER

MIDDLE CEREBRAL ARTERY SAMPLING

What is the appropriate technique for obtaining fetalmiddle cerebral artery Doppler waveforms?• An axial section of the brain, including the thalami and the sphenoid bone wings, should be obtained and magnified.• Color flow mapping should be used to identify the circleof Willis and the proximal MCA.• The pulsed-wave Doppler gate should then be placed atthe proximal third of the MCA, close to its origin in theinternal carotid artery10 (the systolic velocity decreaseswith distance from the point of origin of this vessel).• The angle between the ultrasound beam and the directionof blood flow should be kept as close as possible to 0◦ • At least three and fewer than 10 consecutive waveforms should be recorded. The highest point of the waveform is considered as the PSV (cm/s).

Color Doppler examination of the circle of Willis (left). Flow velocity waveforms from the middle cerebral artery in a normal fetus with low diastolic velocities (right, top) and in a growth-restricted fetus with high diastolic velocities (right, bottom)

MIDDLE CEREBRAL ARTERY WAVEFORM

Fetal middle cerebral arterial (MCA) Doppler assessment is an important part of assessinga) Fetal cardiovascular distressb) Fetal anemia ( Peak Systolic Flow Velocity)c) Fetal hypoxia ( brain sparing effect) It is a very useful adjunct to Umbilical Artery doppler asessment in IUGR fetus.

#A normal fetal MCA S:D ratio should always be higher than the Umbilical arterial S:D ratio. # Measurement of the fetal MCA (PSFV) is a predictor of severe fetal anemia and can be used to avoid unnecessary invasive procedures in red blood cell isoimmunized pregnancies.

INTERPRETATION

# In the normal situation the fetal MCA has a high resistance flow which means there is minimal antegrade flow in fetal diastole. # In pathological states this can turn into a low resistance flow ( reduced PI) mainly as a result of the FETAL HEAD SPARING EFFECT.# Paradoxically in some situations such as with severe cerebral oedema and due to acidemia , the flow can revert back to a high resistance pattern when the pathology hasn't yet resolved which is again an ominous sign and call for termination of pregnancy.

Ductus venosus (DV) flow Doppler  is a useful parameter since of all the pre-cardial veins, the Ductus venosus allows the most accurate interpretation of fetal cardiac function as well as myocardial haemodynamics # First trimester screening : Aneuploidic anomalies

# Second trimester scanning: It is useful in assessing-a) Severity of hypoxemia in IUGRb) Myocardial compromise

DUCTUS VENOSUS DOPPLER

DUCTUS VENOSUS SAMPLING

What is the appropriate technique for obtaining fetalvenous Doppler waveforms?Ductus venosus• The ductus venosus (DV) connects the intra-abdominalportion of the umbilical vein to the left portion of the inferior vena cava just below the diaphragm. The vessel is identified by visualizing this connection by 2D imaging either in a midsagittal longitudinal plane of the Fetal trunk or in an oblique transverse plane through the upper abdomen.• Color flow mapping demonstrating the high velocityat the narrow entrance of the DV confirms its identification and indicates the standard sampling site for Doppler measurements.• Doppler measurement is best achieved in the sagittalplane from the anterior lower fetal abdomen since alignmentwith the isthmus can be well controlled.

This triphasic waveform comprises of S wave : corresponds to fetal ventricular systolic contraction and is the highest peakD wave : corresponds to fetal early ventricular diastole and is the second highest peakA wave : corresponds to fetal atrial contraction and is the lowest point in the wave form albeit still being in the forward direction

DUCTUS VENOSUS NORMAL DOPPLER WAVEFORM

Normal ductus venosus waveform at 12 weeks of gestation with positive flow during atrial contraction.

Ductus venosus flow velocity waveform with low but positive forward flow during atrial contraction.

Ductus venosus reverse ‘a’ waveform

1) Aneuploidic anomalies Down syndrome : ~ 80% are thought to have abnormal waveform2)Congenital cardiac anamolies3)Fetal pulmonary arterial anomalies e.g atresia4) Fetal tumors like sacrococcygeal teratoma5)Twin to twin transfusion syndrome 6) Maternal Diabetes: may exhibit increased PI values Growth restricted fetuses with abnormal Ductus venous flow have worse perinatal outcome compared to those where flow abnormality is confined to the umbilical or middle cerebral artery

ABNORMAL DUCTUS VENOSUS WAVEFORM

Typical progression of multi-vessel Doppler studies with progressive placental dysfunction-

-Elevated umbilical artery S/D ratio-Middle cerebral artery PI < 5th percentile (brain-sparing)-Umbilical artery - absent diastolic flow-Umbilical artery - reversed diastolic flow-Ductus venosus - elevated pulsatility index-Ductus venosus - reversed a-wave-Ductus venosus - decreased IVR, reversed a-wave-Umbilical vein double pulsations-Umbilical vein triple pulsation with reversed a-wave flow

Progressive deterioration in fetal cardiovascular and behavioural variables seen with declining metabolic status.

TAKE HOME MESSAGE#Doppler ultrasound provides a non-invasive method for the study of fetal hemodynamics.

#Investigation of the uterine and umbilical arteries gives information on the perfusion of the uteroplacental and fetoplacental circulations, resp

#Doppler studies of selected fetal organs are valuable in detecting the hemodynamic rearrangements that occur in response to fetal hypoxemia.

contd…

#Doppler velocimetry gives the most important information to differentiate the truly growth-restricted fetus (IUGR) from the fetus that is constitutionally small but otherwise normal in cases where AFV is normal .

#It act as screening as well as diagnostic modality in high risk cases and can guide regarding frequency of follow up & timely intervention.

#Ductus venosus doppler done in the first trimester is a part of screening tools for detecting aneuploidy. contd….

#First trimester uterine artery PI value in high risk cases is being used as a screening tool in few centres to detect preeclampsia cases early .

# Presence of single umbilical artery is not only an indicator of aneuploidy but it also predicts IUGR in 10% cases and calls for suveillance.

#Middle cerebral artery PSFV value has taken over Delta OD 450 in assessing the severity of fetal anemia in Rh alloimmunised fetuses. It is also used to manage such cases by interpreting the rise in Hb in cases of intruterine blood tranfusions and helps in deciding further need as well. ………………………………

UTERINE ARTERY

9WKS

19 WKS

19 WKS

UMBILICAL ARTERY NORMAL WAVEFORM

33WKS|

39 WKS

39WKS

DUCTUS VENOSUS NORMAL WAVEFORM

33WKS

13 WKS

MIDDLE CEREBRAL ARTERY NORMAL WAVEFORM

33 WKS