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What is an Ultrasound
Ultrasound is a scan that uses high frequency sound waves to study internal body structures. The sound waves are emitted from a vibrating crystal in a handheld scanner. The reflected sound waves or ‘echoes’ are then translated into a grainy, two-dimensional (or sometimes three-dimensional) image on a monitor.
Ultrasound is used during pregnancy to check the baby’s development and to help pick up any abnormalities such as Down syndrome. Since the procedure can’t produce high quality images, any suspected abnormalities need to be confirmed with other tests. The ultrasound scan isn’t 100 per cent accurate, but the advantages of the test are that it’s non-invasive, painless and safe for both mother and unborn baby.
Uses of the ultrasound
Ultrasound may be used at various points during pregnancy, including:
First trimester - ultrasound performed within the first three months of pregnancy is used to check that the embryo is developing inside the womb (rather than inside a fallopian tube, for example), confirm the number of embryos, and calculate the gestational age and the baby’s due date.
Second trimester - ultrasound performed between weeks 18 and 20 is used to check the development of fetal structures such as the spine, limbs, brain and internal organs. The size and location of the placenta is also checked. The baby’s sex can be established, if the parents wish to know.
Third trimester - ultrasound performed after 30 weeks is used to check that the baby is continuing to grow at a normal rate. The location of the placenta is checked to make sure it isn’t blocking the cervix.
Different Types of Ultrasounds
There are differences in the types of ultrasounds done during pregnancy. All ultrasounds use sound waves to create a picture. The old standard is a 2D or two-dimensional image. In recent years, 3D or three-dimensional images, and now four-dimensional images or 4D, have become popular. However, 3D and 4D ultrasounds are not considered standard prenatal tests and insurance may not cover the cost of these types of ultrasounds unless your doctor deems them medically necessary.
2D ultrasound gives you outlines and flat looking images, but it can be used to see the internal organs of the baby. This is helpful in diagnosing heart defects, issues with the kidneys, and other potential internal issues.
3D images are used to show you three-dimensional external images that may be helpful in diagnosing issues such as a cleft lip. What 4D ultrasound brings to the table is that as the image is continuously updated, it becomes a moving image, like watching a movie.
Advantages and Disadvantages
Each of these types of ultrasound has advantages and disadvantages. Many families prefer the 3D images because they look more like what they perceive a baby to look like in real life than the flatter 2D images. You should talk to your doctor or midwife about the type of ultrasound he or she uses and why. If your doctor or midwife doesn't offer you a 3D or 4D ultrasound and you'd like one, ask him or her about it.
Reasons for Ultrasounds
Ultrasounds can be used to check a number of variables when you're pregnant, including:
How your baby is developing
Your baby's age
Any problems in your uterus, ovaries, cervix, or the placenta
How many babies you're carrying
Any problems you and/or your baby may be having
Your baby's heart rate
Your baby's growth and position in your uterus
The level of your amniotic fluid
Signs of Down syndrome
Medical issues to consider
Ultrasound is a safe, painless and non-invasive procedure. Many parents consider the ultrasound as an opportunity to see their unborn child, and perhaps discover its sex. However, you should remember that the ultrasound is a diagnostic procedure and, in some cases, it may suggest that a fetus has an abnormality. Further tests are usually needed to confirm the diagnosis.
The procedure depends on the type of ultrasound used, but may include:
Transabdominal ultrasound - sound waves pass very well through water. The sonographer uses your full bladder as a ‘porthole’ to your uterus, so you will have to drink plenty of water before the test. You lie down on an examination table or bed. Gel is applied to your abdomen (to provide better contact between your skin and the scanner) and the sonographer moves the scanner in various positions. Pictures are sent instantly to a nearby monitor. The sonographer may have to push quite firmly at times in order to see the deeper structures. The scan usually takes about 30 minutes.
Vaginal ultrasound - in some cases, a transabdominal ultrasound can’t produce clear enough pictures. There may be too much air in your bowel, for instance, and air is a poor conductor of sound waves. In these cases, a slender scanner is inserted into your vagina. The scan usually takes about 30 minutes.
Immediately after the ultrasound
Once the ultrasound is finished, you are given tissues to wipe away the gel, and you can go to the toilet. The report is sent to your doctor, so you will have to make an appointment to get the result.
There are no known risks, complications or side effects for either the mother or her unborn baby.
Taking care of yourself at home
An ultrasound scan is safe, painless and non-invasive, so there is no need to take any special precautions afterward. You are free to go about your normal business.
Long term outlook
What happens next depends on the results of your ultrasound. Note that a normal result doesn’t guarantee that your baby is normal, because some abnormalities cannot be found using this test. If fetal abnormalities were detected, you may need further tests to confirm the diagnosis. These tests, including amniocentesis and chorionic villus sampling, are optional. Discuss the benefits, risks and complications of these tests with your doctor before deciding whether or not to go ahead.
Other types of pregnancy tests
Other types of pregnancy tests you may be offered could include:
Amniocentesis - a small amount of amniotic fluid is taken using a slender needle inserted through the abdomen. The needle is guided with the help of ultrasound. The fluid sample contains cells, which are then examined in a laboratory for chromosomal abnormalities. The risk of miscarriage following amniocentesis is around one in 250.
Chorionic villus sampling - a slender needle is inserted through the abdomen or cervix to take a small sample of placenta. The needle is guided with the help of ultrasound. The chorionic villi are then tested in the laboratory for chromosomal abnormalities. The risk of miscarriage following chorionic villus sampling is one in 100.
This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.