Important: This is intended as general information only. It may not apply to your specific situation. It is not a substitute for medical advice. If you have a question or concern, please raise it with me at your next appointment or contact me sooner if it's urgent.
There are a few different times in the pregnancy that you may have an ultrasound. At different times in the pregnancy we are looking for different things. Here is a quick summary of the ultrasounds you may have. Not everyone needs all of these scans and some people need many more, this is a guide only.
First Trimester scans
Dating and Viability scan
This is usually done between 6 and 10 weeks (or at your first visit, if that happens to be later). We first look to see that the fetal heart is beating (that is, that the fetus is alive) and then have a careful look within the uterus to see how many fetuses there are (that is, is this a multiple pregnancy). The next step is to measure the fetus to see if your period dates are correct. Measurements at this early stage are very accurate and are generally considered to be more accurate than your period dates, even if you have a regular cycle.
I will always do a dating and viability scan at your first pregnancy visit. Depending on when you book and what appointments are available, this is usually between 8 and 10 weeks gestation. If you wish, you can arrange to come into the rooms earlier than this (especially if you’re not seeing me until 10 weeks) and my midwife (the wonderful Jane) can perform one of these scans for you.
Depending on your gestation and the position of your uterus we may do either an external (transabdominal – or through your abdomainal wall) scan or an internal (transvaginal – the vaginal probe in gently inserted into the vagina) scan. The earlier the pregnancy, the more likely you are to need a transvaginal scan to get a good view of the uterus and the fetus. Don’t worry, anyone who has had one before will tell you that they are nowhere near as unpleasant as they sound!
Nuchal Translucency Scan
This scan is done at approximately 12 weeks gestation and is part of the optional testing for Down Syndrome that many women chose to have done (see the Testing for Down Syndrome page for more information)
This is a very specialised scan and it is very important that it is performed by a skilled and experienced sonographer. I will give you list of ultrasound clinics where you can have this scan performed. In brief, the scan measures the thickness of the fold at the back of the fetal neck. This measurement forms part of the testing we do to see if your baby is at increased risk for Down Syndrome. You do not have to have this test performed.
A transabdominal (external scan) is usually performed but occasionally a transvaginal (internal) scan is required – it’s important to get really good views to get an accurate measurement.
Second Trimester Scan
Also referred to as your anatomy scan or morphology scan, this is your ‘big’ scan where a skilled sonographer has a very careful look at all your baby’s organs to see if they appear normal. It is usually performed between 18 and 22 weeks gestation. Earlier than this, the baby’s organs are still too undeveloped to be able to tell if they are normal or not. Later than this, it gets harder to get good views of the organs – the baby gets progressively more ‘cramped’ and the bones begin to get harder, casting shadows.
If you wish, you can (usually) find out the baby’s gender at this scan. An assessment of the baby’ growth will also be made at this scan, although we often can’t pick big or small babies at this early stage.
Sometimes the sonographer can’t get a good view of one part of the baby (for example, the face or the heart) due to the baby’s position. If this happens, you may need to come back for another scan a few days or a week later.
Like the nuchal translucency scan, it is important to have this scan done by someone very specialised in obstetric ultrasound. The more skilled and experienced the operator, the better the scan. I will give you a list of clinics where the people performing the scans are obstetricians who have done an extra qualification in obstetric scanning. These people spend most of their (professional) time scanning unborn babies and have developed great expertise in this area.
Third trimester scans
A third trimester scan can be done for a number of reasons. Depending on what was seen on the second trimester scan, we may need to do a third trimester scan to ‘follow up on’ or recheck something. If there were no issues of concern on the second trimester scan, it is very unlikely that we would find something of concern on a third trimester scan as the views we get of the baby’s organs are not as good at this stage.
The most common reason to do a third trimester scan is to assess the baby’s growth. This is known as a ‘growth scan’ and is not always necessary. It is performed if it feels like the baby may be ‘too big’ or ‘too small’ clinically or if there is another reason for concern about the baby’s growth (for example, a previous big or small baby or diabetes in the pregnancy). If, from the outside, the baby feels like it is growing appropriately, we generally don’t order one of these scans but if you are particularly concerned and wish to have a growth scan performed, please feel free to ask me about it. Like the second trimester scan and the nuchal translucency scan, the more expert the sonographer, the better the results (that is, the more accurate the estimate of the baby’s size). While I can certainly take measurements on the scanner in the rooms, if I’m worried about the growth of your baby, I will usually send you for a formal scan with an expert obstetric sonologist.
A third trimester scan may also be done to check on the health of the baby if there are any concerns. This involves looking at a number of different things on the scan to perform what is called a ‘biophysical profile’ – a general measure of your baby’s health. Essentially, when we do a biophysical profile, we are looking for any signs that the baby is not getting absolutely everything it needs from the environment in the uterus. This kind of scan might be done, for example, if you had not felt the baby move as much as usual or if you have some bleeding during the pregnancy. This kind of assessment may be done in the course of a growth scan but we can usually perform it for you in the rooms.
Ultrasounds in the rooms
At most of your visits, I will perform an ultrasound scan. This is not strictly necessary – as obstetricians, we can get most of the information we need by feeling your abdomen and listening to the baby’s heartbeat (and only do a scan if we feel it is necessary). However, I feel it offers a nice opportunity to look at the baby and most women find it reassuring and - most of all – fun. It is, of course, completely safe but if you prefer not to have a scan at every visit, please let me know.
I may also perform additional scans in the rooms if there are any concerns. For example, if you have bleeding during the pregnancy or if we have identified that your baby is a little smaller than we might expect for its age. If this is necessary, I will discuss the situation in detail with you.
You may have seen the great 3D (also called 4D) scans available now that almost look like a photo taken from inside the uterus. Many ultrasound clinics will show you a 3D image of your baby as part of one of your pregnancy scans. Although the pictures look fantastic, they don’t add much in terms of diagnosing abnormalities and finding problems – that is still best done with the (usual) 2D scans. Because there is no ‘medical’ indication to have a 3D scan, they don’t attract a rebate from Medicare or your health fund and they are usually not performed by the highly skilled, specialized sonographers you will see for your ‘formal’ scans. Many prospective parents like to have one done as they feel it helps them bond with their baby (plus it’s usually really good fun). Because this is a nondiagnostic, ‘nonMedicare’ scan, you don’t need a referral to have it done. Have a chat with me if you want to get one done and I will recommend a clinic for you.