Ultrasound as a watchdog for pregnancy: Q&A: Dr. Niranjan Chavan & Dr. Narendra Malhotra
M3 India Newsdesk May 20, 2020
From keeping a close eye on an expectant mother’s intrauterine health to foetal health throughout pregnancy, an ultrasound indeed serves as a watchdog of sorts! Eminent OBGYNs- Dr. Narendra Malhotra and Dr. Niranjan Chavan conducted a webinar on M3 India about ultrasound as a surveillance tool for pregnancy. Here we list the Q&A session that followed.
Before the Q&A, here are the take-aways from Dr. Malhotra’s presentation:
- Ultrasonography should be performed using proper guidelines for obstetric USG
- Even a routine USG in pregnancy can help detect many risk factors for foetal and maternal health
- Obstetrical ultrasound facilitates:
- Ruling out ectopic pregnancy
- Foetal cardiac activity/viability
- Chorionicity in multiple gestation
- 20 weeks anomaly
- Knowledge of third trimester growth and liquor
With an audience of more than 1500 users, the Question and Answer session with Dr. Malhotra was highly engaging. Here we have the first set of Q&As which address obstetrics-related questions and the use of ultrasound in pregnancy.
Question 1: How many scans at the maximum can be done in pregnancy; is it safe to do ultrasound each month of pregnancy? Are too many scans harmful?
Dr. Malhotra: Minimum scans are ideally four. After the third trimester, one can do as many scans as are needed, but remember that this means one will also have to fill as many PCPNDT forms. Ultrasound is sound waves, and any energy if focused on one point for hours, will cause heating and cavitation. But, this is a dispersed ultrasound and this whole scan takes about 15 minutes. So, even if one were to focus for say two hours, it raises the temperature by 1 degree. So ultrasound is absolutely safe and so is doppler. Even then, we use a disclaimer on doppler stating- ‘do not use pulse Doppler on the foetal heart’.
Question 2: Can you please comment on the safety of colour doppler in the first trimester of pregnancy?
Dr. Malhotra: There is no problem in the first trimester. Some of us try to take that on the foetal heart and try to hear the foetal heart, and if it is done for a few seconds, it is fine. However so, focused Doppler beam on the foetus’s skull or on the foetal heart in the first trimester is best avoided. Though there is no risk, it is best avoided.
Question 3: Please elaborate on uterine artery doppler.
Dr. Malhotra: There are two uterine arteries coming from both sides. Every artery is muscular- it has an outer core, a muscle and an intima. When a woman’s heart pumps blood, it goes with force to the aorta and the uterine artery. When the uterine artery opens and lets the blood go, you get a systole and a diastole wave. In between the systole wave and the diastole wave is the 'rule of 30'; the diastolic height is 30% of the systole. It applies to any, normal muscular artery.
In pregnancy, the spiral arteries, which are the end branches of uterine, get riffed off by the trophoblast so the resistance is less; plus the hormones are at play. The uterine artery dilates, so after 15 weeks, in the uterine artery wave, the notch is lost and diastole becomes 50%. That is how doppler waves look. Even though the values will be given by the radiologist, sometimes we obstetricians can be poor at interpreting values; so it is best to look at the waves as well.
Question 4: How should one manage Oligohydramnios in the second and third trimester?
Dr. Malhotra: It is first, important to know the cause of oligohydramnios. If it is a placental cause- like if the placenta has not functioned properly, one will have to somehow try and increase the placental blood flow. Some vasodilators like Viagra tablet vaginally, high amino acids, aspirin, and low molecular weight heparin, arginine, nitric oxide donors which will dilate the spiral arteries and improve the blood flow to placenta, can be tried.
Foetal urine can also be one of the main causes of oligohydramnios. If foetal urine is not being formed because of faulty kidneys, nothing can be done. It may not be formed because the foetal kidneys may be receiving less blood. Again, foetal kidneys may receive less blood if the placenta is supplying less blood to the foetus and brain sparing has occurred. Brain sparing causes all the oxygen, which the foetus has received, to go to the brain. This causes the kidney vessels and the coeliac artery of the foetus to undergo constriction so oligohydramnios occurs and the foetal intestine stops functioning. At this point necrotising entercolitis occurs.
Oligohydramnios can only be treated by trying vasodilators but if its maturity and amniotic fluid index (AFI) is less than 5 and the foetus is mature, it is better to deliver rather than taking a risk. Early oligohydramnios is very bad and very dangerous for the foetus.
Question 5: What is normal AFI? What is severe oligohydramnios and when do we call it polyhydramnios?
Dr. Malhotra: Amniotic Fluid Index is done after 28 weeks. The abdomen is divided at the umbilicus into four quadrants, with the patient lying down, so the pregnant uterus is (curved). The probe used has to be perpendicular to the floor. It has to be kept (upright) and the vertical distance has to be measured for all the four quadrants. and added. If it is less than 5, it is oligohydramnios and if it is less than 3, it is very severe oligohydramnios. Five to seven is borderline, 7 to 14 is normal, 14 to 20 is borderline polyhydramnios, and more than 20 is polyhydramnios.
Question 6: Is it fine if only the middle cerebral artery shows abnormal flow and the rest are normal?
Dr. Malhotra: It is not possible that the middle cerebral artery will dilate and the umbilical and uterine will remain normal. But as the first sign, yes, it occurs very early in foetal compromise. The middle cerebral artery will show more diastolic blood flow but at the same time, the umbilical artery will start showing less. So the umbilical cerebral ratio or the placental cerebral ratio, as we call it, will start changing. The uterine artery will also start changing.
Question 7: When do Choroid Plexus Cysts require further investigation? What can we do about them?
Dr. Malhotra: If there is choroid plexus cysts or CPC, it serves as a soft tissue marker. But, if there are no other soft tissue markers like echogenic foci, short femur, or short humerous, then a single CPC has no problem and can be left alone. It can be followed up with ultrasound, and it will mostly disappear. If there is a bilateral CPC, again follow up is needed, and if it does not disappear, the patient can be adviced genetic screening, biochemically or by NIPS to rule out chromosomal anomalies.
Question 8: Can you please explain the ductus venosus flow in the atrial systolic and diastolic?
Dr. Malhotra: Pure blood from the mother comes via the umbilical vein from the placenta. The umbilical vein enters into the liver at an angle, up towards the inferior vena cava because that is nearest. Pure blood goes to the inferior vena cava of the foetus and this opens into the right atrium at an angle, so the pure blood from the umbilical vein through the ductus venosus (the right atrium and the foramen ovale is open) goes to the left atrium, left ventricle, aorta and then the brain.
The blood should go forward in ductus venosus, towards the right. If the blood does not go forward, and diastole is less, it means that the pure blood is not reaching the foetal heart and is collecting back. If it is reversed instead of going forward, it is because the heart is abnormal, because of genetic defects or there is resistance. In that case, the pure blood will not even go into the foetal heart. So, if there is no pure blood in the left side of the heart, only impure blood will circulate in the foetus and the foetus will die.
Ductus venosus flow should always be forward flowing. Even though it is a vein, it is an M-shaped flow because the atrium contracts and gives a wave, a systolic wave and the diastolic wave which is an A wave. The M pattern signifies proper flow. If the M pattern and the A wave become less, it means high resistance. If it becomes reversed, it means that pure blood is coming back and the baby could die within 72 hours.
Question 9: Could you please enlighten us on hydronephrosis in anomaly scan?
Dr. Malhotra: Hydronephrosis is also known as Renal Pyelectasis. The pelvis of the kidney should be less than 3 or 4 mm. If urine is filling in the pelvis of the kidney, it is known as Pyelectasis and this if dilated more than 6 mm is a soft marker for chromosomal anomaly. Or it could be that the ureter could be blocked and the urine does not flow down. This could be blocked in male foetuses because there is a posterior urethral valve so the urine in the bladder could fill up and the back flow could end up causing hydroureter Hydronephrosis or Pyelectasis. Congenital anomaly requires further investigation.
Question 10: If there is a reversal of flow in the uterine artery, should we do ductus venosus doppler or deliver?
Dr. Malhotra: Uterine artery will never show reversal. It will always show diastolic blood flow because it is the mother’s heart so and her heart has the power of both systole and diastole. Moreover, the uterine artery is not a decision-making artery. The decision-making arteries are the middle cerebral, the umbilical and the ductus venosus. Cerebral increasing, umblical decreasing, and reversal of cerebroplacental ratio are considered as risk. If ductus venosus reversal occurs and the baby is mature (more than 28 weeks), deliver immediately. Uterine artery is not used for delivery.
Question 11: In the present scenario of lockdown, what is your advice on first trimester screening?
Dr. Malhotra: Now in some places, first trimester biochemical screening is being done. In areas where courier services have resumed, a person can be sent for sample collection. Big hospitals have been given permission to perform ultrasound too. Patients have to be told to exercise precautions and social distancing. However, if none of these services have resumed, screening can be shifted to 18 weeks. It is mandatory to screen before 20 weeks, also because it helps detect defects as abortion is not allowed after 20 weeks of pregnancy.
Question 12: What is the significance of a single umbilical artery?
Dr. Malhotra: If only a single umbilical artery marker is there, it is not significant. If it is present along with choroid plexus cysts, echogenic foci, short femur, short humerous, or if there are multiple soft markers, a full genetic scan is needed. But if only a single umbilical artery marker is present, and there is specific reason for concern, one may go ahead and do an LIPS, LIPT or an amniocentesis.
Question 13: Can you guide on heterotrophic pregnancy as there are many cases coming in with ectopic or missed ectopic in the first scan?
Dr. Malhotra: The incidence of heterotrophic pregnancies have increased now, with the occurrence being 1 in 10,000 as compared to 1 in 30,000 before. This is because of ART pregnancies. When the embryos are pushed, one of them slips and causes ectopic pregnancy, while the other embryo is in the uterus. Sometimes both of them grow, sometimes either the intrauterine one grows or the other one grows. In such cases, diagnosis comes first.
For all ART pregnancies, scan at 6 weeks and look for heterotrophic pregnancies. If the test is negative, but there is still doubt, call the pregnant woman after a week for another scan. If the ectopic embryo is unruptured and dead, we can let it be. However, if it is live and heterotrophic, a transvaginal needle can be inserted and the material can be aspirated as far as possible (similar to MTP). KCl should be used and not methotrexate as the latter may get absorbed and kill the inrauterine pregnancy. If there is rupture, a laparoscopy can be done to remove the ectopic embryo.
To watch the recorded webinar, click here.
Disclaimer- The views and opinions expressed in this article are those of the speaker's and do not necessarily reflect the official policy or position of M3 India.
Prof. Dr. Narendra Malhotra, a renowned practicing Obstetrician Gynecologist at Agra has special interest in High Risk Obs., Ultrasound, Laparoscopy, ART & Genetics
Prof. Dr. Niranjan Chavan is the Unit Chief in the Dept. of Obstetrics & Gynaecology, at a prominent Mumbai hospital.
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