Ultrasound–Ultrasound technology uses high-frequency sound waves to form pictures of the fetus on a computer screen. The test can verify a due date, determine causes of bleeding, check the overall health, development, sex and position of the baby, measure the amniotic fluid, and check the condition of the placenta. There are no known risks from the tests, and many women have one or two ultrasounds in routine pregnancies. However, there is little scientific evidence that normal pregnancies benefit from ultrasound tests.
An ultrasound scan sends high-frequency soundwaves through your uterus (womb). These 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.
Most parents look forward to their scan because it gives them a first glimpse of their baby. Your sonographer is likely to give you a printout of the image of your baby as a keepsake, although some hospitals charge for this. Treasured though this image will be, remember that the purpose of the scan is not to provide the first photo for your baby album, or to find out your baby’s sex. It is to check that your baby is developing normally.
Who will do the scan?
Scans are usually done 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 do 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 to how your placenta is working. Seeing your baby is also a nice way to bond with him. Although the safety of ultrasounds is not in question, you should always be told 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:
- Check that your baby has a heartbeat.
- Say whether you are pregnant with one baby or more.
- 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.
- Accurately date your pregnancy by measuring your baby.
- Assess your baby’s risk of Down syndrome by measuring fluid at the back of your baby’s neck at 11 to 14 weeks (called the nuchal translucency scan).
- Find out why a blood screening test was abnormal.
- Help with diagnostic tests, such as CVS or amniocentesis by showing the position of the baby and placenta.
- 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.
Will the scan reveal the sex of my baby?
It can do, but not usually until you have an anomaly scan at around 20 weeks of pregnancy. But if your baby is lying in an awkward position it may be hard to tell. Some hospitals or private ultrasound centres have a policy of not telling women the sex of their baby, as it is often not possible to be certain. Read more about whether it’s possible to tell from a scan image whether your baby is a girl or a boy.
How is it done?
If you’re having a scan in early pregnancy, you’ll need to drink a few glasses of water beforehand so that your uterus is pushed out of your pelvis by your bladder, giving the sonographer a good view of your baby. She will put some gel on your tummy and will move a hand-held device, or transducer, over your skin to pick up images of your baby.
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. The sonographer will use a cover similar to a condom and will lubricate this with plenty of gel so it slides in easily. It is not necessary to go in very deeply, and it will not harm you or your baby in any way. Vaginal scans give a much clearer picture of your baby, especially at a very early stage of pregnancy.
Does an ultrasound hurt?
An abdominal scan is painless except for the mild discomfort of 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 women prefer a vaginal scan, as it is best done with an empty bladder. You may feel a bit embarrassed, but remember the sonographer does these scans every day. She 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.
When are scans usually carried out?
- First trimester: If you are very unsure of how many weeks pregnant you are you may be offered an early or dating scan to determine a more accurate due date. If you have had previous miscarriages or have a high risk of miscarriage you may also be offered an early scan. However, in many pregnancies, your first scan will be your nuchal translucency scan (NT scan) which happens between 11 weeks and 13 weeks and 6 days of pregnancy.Read our article about scans in the first trimester.
- Second trimester: Most hospitals and doctors offer a scan at about 20 weeks (the anomaly scan) to check that your baby is developing normally. Read more about scans in the second trimester.
- Third trimester: You may be recommended to have one or more growth scans between 28 weeks and 40 weeks if you’ve previously given birth to a small baby, if you are having twins or if you have other complications, for example, if you are diabetic. Your doctor or midwife may suggest a growth scan if your baby feels and measures smaller than expected. Read more about scans in the third trimester.
Do I have to have an ultrasound?
Although most women in Australia have at least one scan during pregnancy, you don’t have to have one. Scans can give 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 your doctor or midwife recommends a scan and you’d rather not have one, ask her to explain her reasons to you. The final decision rests with you.
What if the scan shows a problem?
You will naturally be very worried if your scan suggests that there is a problem with your baby. Sometimes a clear diagnosis can be made from the scan, such as spina bifida. In other cases, the scan may show minor changes, known as markers, which are usually nothing to worry about, but can occasionally be a sign of something more serious, such as Down syndrome.
If the sonographer finds anything unusual when doing the scan, she should refer you to a doctor. The doctor may recommend doing a further test, such as a CVS or amniocentesis, to see if the baby is developing normally.
If a scan reveals a serious problem, you should be given plenty of support to guide you through all the options. Although such serious problems are rare, some families are faced with the most difficult decision of all, whether to end the pregnancy.
Other problems may mean a baby needs surgery after birth, or even surgery while still in the uterus. Or there may be the need to prepare for a baby who needs special care. There will be a whole range of people to support you through any painful times, including midwives, obstetricians, paediatricians, physiotherapists and the hospital chaplain.
Is 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. Most experts agree that the primary use of ultrasound should be for the purpose of medical diagnosis.