 Today, we will be talking on the technique of obstetric Doppler. We will concentrate only on the third trimester applications of Doppler. The indications are the FGR, the gestational diabetics in twin pregnancies, in post dated pregnancies, also in the assessment of fetal anemia. So, this video we will talk about following key points before you start, which vessels to assess, useful Doppler indices, the technique of basic Doppler tracings, the individual vessel assessment readings normal and abnormal, and few points on the reporting format and the suggestions if any. So, before you start, you should identify the maternal risk factors, not only in the current pregnancy, but also in the previous pregnancy, history of P I H, history of stillbirth, history of diabetes, etc. An assessment of fetal factors is a must in terms of size and proportion, the percentiles of the fetal weight and abdominal circumference, because this is what will tell you if the baby is appropriate for the age or small for the age, the growth velocity, the amniotic fluid volume, and the gross anatomy, of course, whatever can be seen at that gestational age, you should make the efforts to see it. Before you start, you should know the aim of doing the Doppler is to answer two basic questions, is early delivery indicated, and if not, then when to follow up this fetus again for the obstetric Doppler. So, which are the vessels which we insulate, the umbilical artery, the MCA, the bilateral uterine arteries, these are the must. The ductus venous is aortic isthmus, the other venous circulation that is umbilical vein, IVC, sometimes even the intracardiac, the insonation at the tricuspid valve, all these are optional. Whenever there are abnormalities found in the umbilical or MCA or uterine artery, then we try and insulate these other venous patterns or the aortic isthmus. Ubilical indices in the Doppler, well PSV is only useful in vital anemia assessment, that is the MCA PSV. Indices are important because it makes you independent from the insonation angles, which is very difficult to get a constant angle during the obstetric Doppler. The indices are S by D, P i and R i, out of which P i is the only useful Doppler parameter in obstetric Doppler. Why? Because P i gives you the maximum of hemodynamics information and all your stage based protocols nowadays are based on the P i values. How to get a good basic Doppler tracing? Zoom the area of interest, you apply the color Doppler, you should keep the color box narrow because that gives you the best frame rate, then you should apply the pulse wave gate, it should be covering the entire vessel and you to adjust the velocity and filter, all these things mostly are done and set properly by the application specialist, but you should give a thought to it whenever you are doing a Doppler. You should record at least three consecutive uniform waveforms in the absence of fetal body or breathing moments. As you can see here, this is a constant uniform waveform and the machine has done the auto tracing and it has taken the correct waveform. So what you see here is an acceptable waveform, but what you see here is an unacceptable waveform, it is too condensed. There are too many pulses which are seen, so even if the machine does auto calculations, it will be difficult for you to see whether the machine has recorded it correctly. If you want to do a manual tracing, it still will be difficult for you to trace it. Immediately, you should have about 6 to 8 tracings in one image, not more than 10 tracings in that one image and that spectrum should occupy the entire image of the spectral waveform so that you can analyze it properly. As you can see here because of the movements, some tracings are coming very faint, some are coming good and if you do the auto calculation or auto measurement, see the machine is not really calculating it properly. So even if you try to do manually, you will see that these three waveforms are at least constant, but in the manual or in an auto tracing, if the machine calculates this particular waveform, now it is going to be not a very correct measurement. So you should see to it that you have a uniform tracing of any artery which you are insonating. Now we will come to the individual tracings. The umbilical artery, you should visualize a cord, you should ideally select a free loop. Doppler indices measured at fetal end at the free loop or at the placental end have a difference in their PI values. Impedance is highest at the fetal end, so that is why the free loop is better. Sometimes if you take it too much near the placental end and if there are fetal parts, especially in olicohead ramneas, then it in fact tends to compress the vessel and you don't get a good tracing. But again in olicohead ramneas, it may be difficult to get a free loop also. So ideally a free loop is better, but then as in cases of twins, you will not be very sure which twin Doppler this umbilical artery belongs to. So it is always better to do the sampling towards the fetal end in cases of twins. Due to zoom it up, the 2D image in freeze mode provides a better Doppler tracing, so you should always do it in a 2D image which is frozen and the values of PI more than 95th percentile are actually significant of the abnormality. So as you can see here, you have magnified the image, you have put in the spectrum and then this is the normal spectrum, when around 35 percent of placental underperfusion is there, what you see is the reduced forward diastolic flow, then whenever there is around 50 percent underperfusion, you will see absent forward diastolic flow and whenever there is 70 percent or more of underperfusion, you will start seeing the reverse diastolic component. As you can see here, this fetus is breathing and then that is why you get this chaotic kind of a pattern which is not correct to trace, you will have to wait for fetal quiescence and then take the tracing, only then you will get a correct PI value. Now in this case, if you see there was an absent forward diastolic flow at free loop, but there was a reverse diastolic flow at the fetal end. So you have to be careful, that is why it is always better to take 3 or 4 measurements at different places and then record the findings. And of course, though we know the PI more than 95 percentile is significant, you can easily go to this site and then check your percentile, we will see it in the end how easy it is. The MCA is taken in an axial section, the color Doppler, power Doppler is taken at the proximal third of the middle cerebral artery, you should put your spectrum somewhere near its origin and not at the far end. The angle of intonation should be as close to zero as possible. You should always remember to avoid unnecessary pressure on the head. And whenever you are taking it for the anemia, you have to take the highest point of waveform for the PSV. Sometimes in these 3-4 tracings, one may be a little shorter than the other, so you should take only the highest PSV. Continuous low velocity forward flow is seen in a normal MCA spectrum. In a brain-sparing phenomenon, there is vasodilatation and that is why there is low PI, which will be less than 5th percentile. And of course, PSV in anemia is taken in terms of MOMs, which is more than 1.5. Again at the perinatology website, you will find the correct MOMs, the percentile of the MOMs. So, this is how you should take a tracing. This is the color Doppler picture and this is where you do the intonation, as you can see the angle is very low as much as 15 to 20 degrees and this is your normal tracing. If you give unnecessary pressure, in fact, this is how you start seeing a pulsatile pattern. You tend to lose out on this forward diastolic flow, so you should not give unnecessary pressure on the head to get a good spectrum. So, this is what a normal waveform looks. There is a forward diastolic flow, but the percentage of that forward diastolic flow is not as high as the umbilical artery. So, whenever there is vasodilatation, there is a more forward diastolic flow, brain tries to get in more blood and that is why you in fact start seeing it as the umbilicalization of the MCA. This spectrum almost looks like the umbilical artery. And of course, this PSV is about 122 and which is this was at the gestational age of 25 to 26 weeks, which was very high. So, this was a case of fetal anemia. Now, another important parameter is the cerebral placental ratio. It is the ratio of MCA-PI upon umbilical artery PI and it is now considered as the most sensitive marker for the redistribution of the blood in fetal hypoxia. The CPR may be abnormal even when individual PI in MCA and umbilical artery are within normal limits and that is why this is the single most parameter, which is important. The CPR less than 5th percentile again is considered as abnormal. With that, we come to a uterine artery Doppler. You have to place the probe longitudinally in the lower lateral quadrant. The color flow mapping is useful to identify the uterine artery which crosses over the iliac artery and the sample volume is placed in 1 centimeter downstream from this crossover point. So, this is the iliac vessels artery and vein and this is the uterine artery which crosses over. So, your spectrum has to be within 1 centimeter of this crossing over. This is the spectrum which we get in till second trimester, but this is how we see it usually in the third trimester. There is a very high forward diastolic flow. Again, here the PI is important and PI more than 95th percentile is abnormal. The ductus venosus is an optional finding, is an optional dressing, but one should know it because it is there in the Barcelona stage based management protocol. So, how do you take it? It is in the mid sagittal longitudinal plane or in an oblique transverse plane. So, in the third trimester, the oblique transverse plane becomes much easier to insulate. On color Doppler there is a high velocity turbulent flow at the narrow entrance of the ductus venosus and it confirms its identification and you have to put the pulse Doppler on. As you can see here, it is showing you that pulsatile, this is the high velocity jet. Outlined by the bright, ecogenic line is the ductus venosus. The S, D and A valve are the normal pattern and this is the pulsatile pattern and this is a reverse A valve pattern which is an abnormal thing. So, usually there is a biophysics spectrum, continuous flow throughout the atrial contraction. There is high PIMO than 95 percentile is abnormal. Absent forward flow during atrial contraction and reverse A valve are the abnormal findings and this is the strongest single Doppler parameter to predict the short term risk of the fetal death, especially in early onset FGR. Aortic isthmus again is important because the reversal of flow in the aortic isthmus precedes ductus venosus abnormalities by one week and that is why it is very important. It always has forward flow during diastole and reversal, it is a marker of poor neurological outcome in an FGR fetus. Again, a sagittal section is difficult to obtain because of the shadowing of the surrounding structures. So, in a three vessel trachea view, this is the SUVC aorta and pulmonary and this particular area where I put the spectral pulse Doppler on is the aortic isthmus. Normally, you see this forward diastolic flow and there is a reversal of flow in an abnormal fetus. But again, there is lot of surrounding overlap of the spectrum and it is a difficult or not very easy vessel to insulate. So, decision about waiting versus delivering when it is important, the aortic isthmus becomes an important parameter. So, we will see how once you go to this site, you go to these Doppler pressings and then you will get this, you can press on the umbilical artery or middle cerebral artery, you have to put in your gestational age in weeks and in days and your pulsatility index and it gives you whether what is the percentile and whether it is normal or not. Same is true for the CPR, you have to put the PI of the middle cerebral artery, PI of the umbilical artery and then it gives you the ratio, its percentile and whether it is normal or pathological. So, in the end, we will come to the reporting format. You have to always talk about biometry, AFI, the fetal behavior that is biophysical profile. You have to give in a tabulated format the umbilical artery to a three readings, the MCA, bilateral uterine arteries and the CPR. The ductus venousis is optional, aortic isthmus is optional whenever indicated. PI is the only reading which is important, giving percentile is a good practice point useful for the fallout scans. The cord around the neck of course it is a big query but then gynecologist expects you to write that during the report. So, this is how in the tabulated format you can give the different readings and its percentile and the report should talk about the umbilical arteries, uterine, middle cerebral arteries with normal color, flows, normal spectral pattern and PI values, no fetroplacental or a neutroplacental insufficiency, the cerebroplacental ratio is normal and no nuclear cord surrounding the fetal neck at present. If the report is normal, then depending on the indication that is PIH, a small size baby or depending on the gestational age of a fetus, a follow-up should be advised. Usually when the Doppler is normal, a two weeks follow-up is good enough. When the Doppler parameters are abnormal, the Barcelona protocol for stage base management is to be followed. We will not be discussing about it in this video but we will talk about it in our next video. Thanks for watching.