Ultrasound in Obstetrics

This this episode of PodMD, A/Prof Louise Kornman and Dr Deborah Nisbet from Women’s Ultrasound Melbourne (WUMe) will be discussing the topic of ultrasound in obstetrics, including what ultrasound is, how it is used in obstetrics, the limitations of ultrasound in obstetrics, the information contained within a ultrasound report and more.

  • Transcript
    Please note this is a machine generated transcription and may contain some errors.
    *As always, all in this PODMD podcast is intended for health professionals and the comments are of a general nature. Information given is not intended as specific medical advice pertaining to any given patient. If you have a clinical issue with one of your patients please seek appropriate advice from a colleague with expertise in the area.

    Today I’d like to welcome to the PodMD studio A/Prof Louise Kornman and Dr Deborah Nisbet, from Women’s Ultrasound Melbourne, or WUMe for short.
    WUMe is a specialist ultrasound clinic with four practice locations across Melbourne in East Melbourne , Parkville, Glen Iris, and Black Rock.

    Our first speaker today is A/Prof Louise Kornman. Louise completed her medical training at the University of NSW and her early training in obstetrics and gynaecology at Westmead Hospital in Sydney. She has, until recently, been Clinical Associate Professor of Obstetrics and Gynaecology at the University of Melbourne and a consultant Ultrasonologist and a member of the Fetal Medicine unit at the Royal Women’s Hospital.

    Our second speaker today is Dr Deborah Nisbet. Debbie is the Deputy Director of Obstetric and Gynaecological Ultrasound Services at the Royal Women’s Hospital. For a number of years, Debbie has been involved in ultrasound training and accreditation in a range of roles at RANZCOG, including ultrasound sub-speciality chair, examiner and contributor to the nuchal translucency online learning program. She has studied endometriosis scanning in Brazil and maintains a particular interest in this area.
    Today, we’ll be discussing the topic of ultrasound in obstetrics.

    *We do hope you enjoy this podcast but please remember that the advice here is of a general nature and is not intended as specific advice about a given patient. The views and opinions expressed in this podcast are those of the doctor, not PodMD.
    If you do have a patient on whom you require specific advice, then please seek advice from a colleague with appropriate expertise in that area.

    Louise and Deborah, thanks for talking with us on PodMD today.

    Answer: Thank you for having us.

    Question 1
    The topic of today’s discussion is Ultrasound. Can you describe for our listeners how does Ultrasound work?

    Answer: Ultrasound uses sound waves at very high frequency. It levels beyond our hearing, the ultrasound transducer sends out sound waves which pass through the gel which is applied to the probe or the skin and into the tissue of the person having the Ultrasound. The sound waves then travelled through the tissues and bounce back to the tribute transducers to form an image on the screen and and thereby we’re able to get a visual image of what’s going on beyond our actual site.

    Obviously, there are a lot of machines settings involved in obtaining the images and the person performing the scan needs to drive the machine appropriately to get the best images they can. They do this by altering the machine settings, the position and the angle of the transducer and often by applying pressure to reduce the interference of tissues between the transducer and the areas being imaged.

    The thing we always try to do with any ultrasound, and particularly in obstetrics, is to abide by the ALARA principle, which means doing apply it as low as reasonably achievable. On the basis that although we know of no harm caused by ultrasound, particularly in a developing foetus, we want to minimise any potential risk that may become evident in years to come. So far, nothing has really been shown as a problem, but this we we don’t want to take any additional risks.

    Question 2
    How is ultrasound applied in obstetrics?

    Answer: Obstetrics is particularly well suited to ultrasound imaging as the foetus is surrounded by fluid. The ultrasound beam passes readily through the fluid without it interfering with the ultrasound beam, and it’s possible to obtain very clear images of the foetus. Ultrasound allows us to count how many foetuses are presen, to assess the structure of the foetus at different stages of development, to measure the foetus ,to look at the details of the placenta and the amniotic fluid, to visualise the uterus, including the cervix, and to look at the maternal ovaries. Ultrasound is applied in different ways throughout pregnancy.

    Question 3
    What type of conditions can you identify using ultrasound in obstetrics?

    Answer: The conditions change a little according to the stage of the pregnancy we’re doing the ultrasound. Very early in pregnancy we’re basically using it to confirm that there is a pregnancy and that it’s developing normally that it’s in the correct position within the uterus. Miscarriage can be diagnosed, ectopic pregnancies can be diagnosed if done at the appropriate time and not too early.

    Twins and other multiple pregnancies can be diagnosed after about six weeks usually and the age of the embryo or the pregnancy can be calculated, and it’s thought that if you do an ultrasound early in pregnancy that this may be slightly more accurate other than dates alone in the when looked at in the bigger populations.

    So early in pregnancy, we often find that vagina ultrasounds are required because this allows us to get our ultrasound probe closer to the area of interest, which is the developing pregnancy. Once you get to about 12 or 14 weeks and we’re in all of these, of course we’re talking about gestational age, meaning the foetus is actually only 10 to 12 weeks in development. The foetus is amazingly well developed, and it’s possible to assess the foetal anatomy in quite some detail.

    So you can see that the skull has formed. You can see the lenses of the eyes. You can see the feet. You can check the that the baby’s got 4 chambers to its heart and you can even count the fingers, so it means that many foetal abnormalities which in years gone by, used to only be detected at that mid trimester scan, can be seen at an early stage. One of the particular things we look at in the first trimester is the nuchal translucency, that fluid behind the back of the foetus neck, which can be a sign of chromosomal abnormalities, in particular, Down syndrome.

    The role of this has become perhaps a little less important now we have other modalities such as NIPT and so on, to which will better at diagnosed Down syndrome, but it’s still a very useful measurement, as other conditions can be highlighted by this, such as cardiac abnormalities or other chromosomal abnormalities not found in the NIPT.

    The foetal anatomy gets more detailed and or we’re able to see it in more detail as the pregnancy progresses, so that by about 20 weeks, 20 plus weeks, we perform our morphology scan in years gone by this was the one and only scan performed and if there is only ever one chance to do it, this is still the best. It enables us to cheque the structure of the foetus and usually results in a and what we would consider a normal scan. We are looking for foetal abnormalities so we do continue to look at all the structures that we possibly can see. So we look at the developing brain, which is the least developed of all the structures, the heart, the kidneys and so on. We checked the limbs, the spine, kidneys and all the things that we can possibly see.

    We also checked the surrounding tissues, such as the amount of fluid, the placenta, and where it’s cited, the cervix, the length, and we also have a look out at the ovaries and just as a since we’re there just checking that there’s no obvious abnormality that may impact the pregnancy or the mother such that the pregnancy might be impacted.

    After the 20 week scan, most scans are directed at detecting problems with foetal growth and placental function or with the location or the function of the placenta. While we are doing these scans, we also do a brief check of the foetus just to make sure that there are no new or previously unnoticed abnormalities that have developed in the meantime.

    Question 4
    What are the limitations of ultrasound?

    Answer: Limitations of ultrasound can be divided into technical limitations and embryological and developmental limitations. Ultrasound waves are affected by the tissues that need to pass through, which can result in a very fuzzy image in poor views for diagnostic ultrasound. For this reason, we compress maternal tissues, move the transducer about to try and get a clearer window, and try and scan through the thinnest part of the abdominal wall.

    So for example, when we think of abnormalities of foetal development, it’s generally only possible to detect abnormalities of structure at the time of the scan. The foetus needs to be developed to a stage where a structure is visible on ultrasound and it needs to be technically possible to visualise that structure. It may not be possible due to foetal size at the time of the scan or due to technical limitations in visualising a particular foetus, for example, foetal position, or the thickness of tissues affecting the passage of the ultrasound beam to the foetus, more detailed foetal anatomy, is seen at 20 weeks, then at 13 weeks of pregnancy, as there is more development of the foetus and there is also increased foetal size, but some conditions are still unlikely to be visualised at 21 weeks due to technical and developmental limitations in some cases.

    Some examples of things that may not be detected at 21 weeks would be abnormalities of foetal growth, obviously, but also our development of the skeletal system such as Achondroplasia, major bowel blockages such as Duodenal atresia and conditions which may evolve such as fluid on the brain or ventriculomegaly.

    The structure of the heart and brain are seen in increasing details at the foetus grows and in some cases you may still not be able to see things as well as you’d like to, so further information may be required through genetic testing on the amniotic fluid or an MRI may be suggested to get further information.

    Question 5
    Are there optimum times for patients to have their scans?

    Answer: Yes, there are better times to have scans, depending on which of course you’re trying to achieve. If people want to confirm that they are pregnant and in the right place, then we would ideally like to do this after six weeks gestation, i.e., four weeks embryonic age. By that time we should in fact, just over six weeks we should be able to see an embryo and possibly a heart activity at this time, which confirms it’s in the right spot, the dating and that at that point anyway, the foetus is alive.

    If there’s an increased risk of an ectopic pregnancy and a woman, we are happier to do it be a little before that round five weeks just to see if we can see any sign of a gestational sac within the uterus. We may have to say it’s a pregnancy of unknown location if we can’t see a gestational SAC anywhere and then we will rely on the beta HCG levels to get to a certain level before being able ,being more confident that our ultrasound is telling us what we would, that it it is or isn’t an ectopic pregnancy.

    Beyond that, six week scan or six to 7-8 weeks if you want to cheque on position and viability, we would then jump prob most likely to about over 12 weeks ’cause the next scan is usually for this nuchal translucency, or what used to be known as the nuchal translucency scan and that’s done from 12 weeks to about 13 weeks and six days if you want the nuchal translucency assessed and at that stage we will also cheque the foetal anatomy for those people who aren’t interested in assessing the risk for down syndrome, we still consider it a very worthwhile test because we can detect problems in early foetal growth, which may be a harbinger of potential foetal demise. We can cheque for some structural abnormalities and things like, for instance, sounding carefully which might otherwise not even be shown up till the 20 week scan, so it seems a shame to miss out on basic structural knowledge just because people don’t want to know about their risk Down syndrome.

    So about 70% of structural abnormalities that would develop at the mid trimester scan. Sorry that we detected the mid trimester scan can be seen at the nuchal translucency scan. Yeah, and for many couples it’s easier to make a decision about what to do with the pregnancy earlier rather than waiting till 20 weeks plus to make that decision.

    The next usual time for doing scans, unless there’s a problem found, so you will often find that if we think we see a problem such as a cardiac problem or a thickened nuchal translucency that doesn’t turn out to be Down syndrome, we may suggest a 15 to 16 weeks can just to confirm or refute our what we thought we could see at 12 weeks, but otherwise most scans we do then again around the 20 to 21 week mark, at which stage that’s a we can get a better view of the foetal anomalies and we pick up hopefully that other 30% that weren’t noticed at the first time.And that’s the most thorough foetal scan, although we do acknowledge that from then on, it’s possible that things can develop and develop poorly from them.

    You can do a full morphology scan earlier than that, but the earlier you do it number one, the less developed the foetus potentially is, the less chance there’s been a problem developing and also the more difficult it is to see often that the foetus is smaller and hence images aren’t as clear. Earlier scans are often done transvaginally, particularly in the first trimester, second trimester some foetuses are better visualised with the transvaginal scan, if ever we want to cheque cervical length thoroughly, we do that transvaginally as well.
    Most 20 week scans need to be done transabdominally again, if we need to cheque the cervix or a placental site, we may do that vaginally, but the vast majority can be better seen at Transabdominally. Later on we will do the the pregnancy scan at any stage but as required for assessment of foetal well being.

    So yeah, it’s important that people don’t feel that they want to have all of their scans done as early as possible within each of those ranges of gestation, so if someone presents at just over 12 weeks gestation, they’re more likely to get suboptimal images than if they have the scan done at over 13 weeks, and they’re also more likely to end up having a transvaginal scan and it’s likewise it is important not to book for the mid trimester scan too early and rushed to have it at 19 to 20 weeks. You’ll get much better pictures at around 21 weeks gestation and if you acknowledge that you have a thicker abdominal wall than having the scan done at around 22 weeks, it’s a good idea if you’re wanting to get optimal pictures.

    And sometimes we have to tell women that we haven’t been able to, despite our best attempts, and looking on several occasions on the same day, we are unable to get the sort of views we would like to be able to get and we may ask them to come back in three or four weeks time to optimise the views we can get.

    Question 6
    What other tests and examinations are available for obstetric patients?

    Answer: As we mentioned with the nuchal translucency can be measured at 12 to 13 + 6 weeks gestation, and this can be used to calculate a chance of the foetus having Down syndrome. But the detection rate is increased by combining the ultrasound with the maternal serum screening blood test and it’s higher still if you have NIPT witch Louise mentioned earlier on.

    Other ultrasound features, in particular the nasal bone, can also be included in the risk assessment for Down syndrome and the nasal bones also, an important structure to see in any foetus, thinking of all sorts of other problems that can be associated with an absent nasal bone. At 12 to 13 weeks + 6 days, ultrasound of the pregnant women’s blood vessels supplying the uterus or the iterate artery dopplers, can also be used as part of the calculation of risk of preeclampsia occurring later in pregnancy and if the risk is found to be increased, aspirin can be used to help to reduce this chance.

    Either foetal abnormality or growth disturbances detected at any stage of pregnancy and at pregnancies at risk of other complications, such as foetal anaemia, this can be monitored with ultrasound as well. Ultrasound can be used to measure the foetus and plot those measurements on graphs to compare with the expected foetal size and ultrasounds also used to estimate the quantity of fluid around the foetal and to perform detailed blood assessment and observe foetal movements.

    Ultrasound can be used to guide diagnostic procedures such as Chorionic villus sampling and amniocentesis. The needle used for the procedure is clearly visible in the ultrasound image and less commonly interventional procedures such as blood transfusion, foetal blood transfusion are required, with ultrasound used to guide the procedure.

    Question 7
    What type of information is contained within a report?

    Answer: Within a report we usually start with the reason for performing the scan, which will be that that’s provided by the doctor, but also any additional relevant information we feel is worthwhile included at the top, such as other problems they have had to put it into context. We then in a pregnancy will write the due date based and usually on the 1st available scan, but there may be comments made about some discrepancy between the two, we’ll comment on the current age of the pregnancy and the number of foetuses.

    There’s information about the foetal movements, the placenta, well more the placental site, the central structure has not been shown to be particularly useful in telling us about its function, the amniotic fluid amount and the foetal measurements and information about the foetal structure and anatomy. Later in pregnancy there’s also information information about the position of the foetus, such as whether it’s headfirst breach, what type of breach it is, with a view to the imminent labour.

    And information about the pregnant women’s soft pelvis, including the cervix, ovaries and fibroids may be included if relevant. A conclusion is included and we will often make recommendations if they’re relevant we feel to the pregnancy and the person managing that pregnancy.

    The doctor performing the scam will keep the patient informed during the scan and discuss any unexpected results with them and if required, they’ll get in contact with their referring Dr and discuss and arrange further management and follow up.

    Concluding Question
    Thank you for your time here today in the PodMD studio. To sum up for us, could you please identify the three key take home messages from today’s podcast on Ultrasound in Obstetrics?

    Answer: I think it’s important that people understand how ultrasound works, so they can better understand why we apply pressure., look through slipper parts of their abdominal wall and offered transvaginal scans for example. And it’s important for referring doctors to understand how ultrasound works as well, and the limitations of what we can offer on ultrasound and making sure that patients are referred at the correct time of pregnancy to get the best possible images.

    Pregnancy ultrasounds are generally a joyous occasion, but there are serious aspects to the scan and the doctor performing the scan will be aiming to obtain the best possible diagnostic images and provide a meaningful and comprehensive report about the pregnancy to both the patient and to the referring Doctor.

    Yeah, and as was just stated, we really, we’re not doing people any favours by seeing them too early unless they’re about to jet off somewhere. But on the whole, sticking to the times we suggest so later rather than earlier for the 20 week scan and a good 12 1/2 to 13 weeks for the first trimester scan is worthwhile because it means hopefully with only one investigation at those times, the patient will get the information they and we are requiring.

    Thanks for your time and the insights you’ve provided.

    Answer: Thanks very much for having us. Yes, thanks for listening to our thoughts on ultrasound.

*As always, all in this PODMD podcast is intended for health professionals and the comments are of a general nature. Information given is not intended as specific medical advice pertaining to any given patient. If you have a clinical issue with one of your patients please seek appropriate advice from a colleague with expertise in the area.