Ultrasound : Overview
Updated: Feb 5
What is an ultrasound scan?
An ultrasound scan sends high-frequency sound waves through your uterus (womb). These sound waves bounce off your baby and the echoes are turned into an image on a screen that shows your baby's position and movements.
Hard tissues, such as bone, reflect the biggest echoes and are white in the image, and soft tissues are grey. Fluids, such as the amniotic fluid that your baby lies in, appear black because the echoes go through them. Your sonographer (the person performing the scan) will look at these shades to interpret the images.
Who performs the scan?
Scans are usually conducted by radiographers or midwives who are trained in ultrasound, and are known as sonographers. Most have a post-graduate certificate, diploma or master's degree in medical ultrasound.
Special scans may be needed in some pregnancies and these will be carried out by a doctor trained in ultrasound, known as a maternal fetal medicine specialist.
If you are seeing a private obstetrician or an obstetrician in a public hospital, she may also conduct a short scan at some of your antenatal appointments. These scans can be used to check the general health and growth of your baby and the how your placenta is working. Although the safety of ultrasounds is not in question, you should always be advised about what the purpose of a scan is and have the right to refuse, especially if there is no medical reason for its use.
What is an ultrasound scan used for?
Depending on which stage of pregnancy they are done at, scans can:
Accurately date your pregnancy by measuring your baby.
Determine whether you are pregnant with one baby or more.
Check that your baby has a heartbeat.
Examine your baby to see if all their organs are normal.
Detect an ectopic pregnancy, where the embryo implants outside the uterus, usually in the fallopian tube.
Find out the cause of any bleeding you may be having.
Assess your baby's risk of Down syndrome (nuchal translucency scan).
Determine why a blood screening test was abnormal.
Diagnose certain abnormalities, such as spina bifida.
Assess the amount of amniotic fluid you have and find out where the placenta lies.
Measure your baby's rate of growth over several scans.
How is an ultrasound performed?
If you're having a scan in early pregnancy, you will be required to drink a few glasses of water prior so that your uterus is pushed out of your pelvis by your bladder. This will give your sonographer a good view of your baby. Your sonographer will apply some gel on your tummy and move a hand-held device, or transducer, over your skin to pick up images of your baby. This is known as an abdominal scan.
If your baby is still too deep in your pelvis, or if you are overweight, the images will not be very clear, so a vaginal scan may be necessary. The vaginal transducer is long and narrow to fit comfortably inside your vagina. It is not necessary to go in very deeply, and it will not harm you or your baby in any way. Vaginal scans provide a much clearer picture of your baby, particularly during the very early stages of pregnancy.
Does an ultrasound hurt?
An abdominal scan is painless except for a mild discomfort from the transducer pressing on your tummy if you have a very full bladder. You won't usually be asked to fill your bladder for scans in later pregnancy, but check with your midwife or doctor first.
Some pregnant women prefer a vaginal scan, as it is best performed with an empty bladder. Your sonographer will cover you with a sheet, and, if you relax your muscles so that the transducer can slide in easily, it should not be uncomfortable.
Will the scan reveal the sex of my baby?
If you have elected to find out the sex of your baby, an anomaly scan can typically be performed around 20 weeks of pregnancy, however is not 100% accurate. The accuracy of the scan can be influenced by a number of factors including the age of your baby, the equipment used, the technician, and the cooperation of the baby.
When are scans usually completed?
All women are offered ultrasound scans in pregnancy, but the number and the timing will vary depending on your healthcare provider, whether you are a public or private patient, your own pregnancy health and any previous medical or pregnancy problems you may have had.
As a general guide they may include:
6 – 10 weeks: early scan.
10 – 14 weeks: dating scan.
11 – 14 weeks: nuchal translucency scan.
18 – 20 weeks: anomaly scan.
Your doctor may also offer you additional ultrasound scans at your antenatal appointments in order to check the health of your baby and rule out any problems.
What if my scan shows a problem?
Scans, particularly in the first trimester of pregnancy, can be an amazing and exciting experience, it's wonderful to see a little blob with a heartbeat that will become your baby. However scans can also be quite worrying, particularly if your scan suggests that there is a problem with your baby. Sometimes a clear diagnosis can be made from the scan, however in other cases the scan may show minor changes, known as ultrasound markers.
Markers are slight deviations from the normal anatomy seen on a scan. It's important to remember that most babies found to have markers are actually normal babies. Some of these are transient findings which may disappear within weeks. The presence of markers slightly increases the chance of there being certain chromosomal abnormalities, however these can only be accurately diagnosed by CVS or amniocentesis.
Problems may mean a baby will require surgery after birth, or even while still in the uterus. Or there may be the need to prepare for a baby who needs special care. If any problems are revealed you will be provided with plenty of support and guidance through your options and the painful times, including midwives, obstetricians, pediatricians, physiotherapists and the hospital chaplain. Although such serious problems are rare, some families are faced with the most difficult decision of all, whether to end the pregnancy.
Is an ultrasound safe?
Ultrasound has been used in pregnancy for nearly 30 years and there are no known side-effects. No link has been found between scans and a baby's birthweight, childhood cancer, sight and hearing problems, or dyslexia.
Do I have to have an ultrasound?
Although most women in Australia have at least one scan during pregnancy, you do not have to have one. No obstetric scan is obligatory in pregnancy, it is always your choice. Scans can provide useful information about your pregnancy, and most women find them reassuring. However, many abnormalities cannot be seen on scan, and sometimes the scan findings can cause worry.
If you have reason to be worried about your pregnancy in the early weeks, then an early scan may be a good idea. If you are not sure of your due date you may need to have a dating scan.
You may choose to have a nuchal translucency ultrasound between 11 weeks and 13 weeks and 6 days of pregnancy. If you choose to have a combined ultrasound with blood test you can have the blood test between 9 weeks and 13 weeks and six days of pregnancy.
It may be that the only scan you need or want during your pregnancy is the anomaly scan at 20 weeks.
Of course, you may not wish to have a scan at all and this can be discussed with your doctor or midwife. Or, you may want all of them, in which case you may like to ask the following questions:
What do I need for my health and my baby’s health?
What is available locally?
What can I get elsewhere?
What is available on Medicare?
What is available privately?
Speak to your doctor or midwife about the reasons you might wish to have the scan done. If your doctor or midwife recommends a scan and you'd rather not have one, ask them to explain their reasons for doing so, but the final decision rests with you.
Pregnancy ultrasound scan: an overview - Approved by the BabyCenter Australia Medical Advisory Board