The 18-20 week Prenatal Ultrasound
Prenatal ultrasound has become an important part of prenatal care. Before making a choice about prenatal testing, it is helpful to have information about the purpose, benefits, limitations, risks and consequences of testing. This information provides you with answers to common questions asked about the 18-20 week ultrasound.
What is prenatal ultrasound?
Prenatal ultrasound (also called a sonogram) is a test that creates pictures of your baby’s body and internal organs using ultrasound waves. These pictures provide information about the health and development of your baby and pregnancy.
Why is prenatal ultrasound done?
Prenatal ultrasound is performed for a number of reasons, including to:
- make sure your baby is alive and growing
- determine if there is more than one baby
- date the pregnancy accurately and determine if your baby is too small or too large for your dates
- assess the risk of Down syndrome and other chromosome conditions
- evaluate your baby's heart rate, movement, and the amount of amniotic fluid (called a biophysical profile)
- check for serious birth defects
Should every pregnant woman have an ultrasound?
The Society of Obstetricians and Gynecologists of Canada and the College of Physicians and Surgeons of Alberta recommend that all pregnant women be offered the option of an ultrasound in their 18th to 20th week of pregnancy.
How is an ultrasound done?
You will be asked to drink one or two glasses of water an hour before your ultrasound. A fuller bladder pushes the uterus closer to the surface of your abdomen which allows for clearer pictures. The ultrasound is done in a small, dimly lit room that has a small bed for you to lie on and a large ultrasound machine. Because of this, we asked that you limit the number of people with you. If you bring your children, please bring a caregiver who will be able to take care of them in the waiting room if they become restless.
Your ultrasound will be performed by a trained specialist. Some gel will be spread over your abdomen and a small hand-held device called a transducer is gently rolled over your abdomen. Sound waves travel through your abdomen and uterus and bounce off different internal surfaces. Echoes from the sound waves are then converted into an image and onto a television monitor to produce the pictures.
It usually takes 20-45 minutes to complete the ultrasound.
How do I get my ultrasound results?
Check with your prenatal care provider when the ultrasound is booked or with the facility that you are attending as to how you will receive your results.
Is prenatal ultrasound safe?
Ultrasound is considered a safe procedure for both the woman and her baby. No radiation is used with ultrasound. Although there is no evidence of harmful effects, an ultrasound should only be done when there is a medical reason for the test.
What are the benefits of an 18-20 week ultrasound?
Most women would say that having an ultrasound reassures them and gives them peace of mind. The ultrasound can be an exciting and positive experience for you and your partner.
What else do I need to know before proceeding with an 18-20 week ultrasound?
Although prenatal ultrasound is simple and painless, some women and their partners find the experience stressful.
Does an ultrasound finding mean that my baby will have problems once delivered?
No. Ultrasound has improved so much over the years that minor differences in organ development may be detected. Some of these differences are called “markers”. While markers are often seen in normal babies, they are more commonly seen in babies with chromosome conditions such as Down syndrome. Examples of markers linked with Down syndrome include:
- Nuchal fold (thickness at the back of the baby’s neck
- Echogenic bowel (brightness of the baby’s intestine)
- Echogenic foci (bright spot in the baby’s heart)
What do 18-20 week ultrasound markers mean?
Markers do not harm the baby.
A marker may increase the risk , but does not mean that the baby definitely has a condition such as Down syndrome. Most markers are identified in healthy babies. If a marker is found, you will be given the option for more counselling or testing. This may include a referral for genetic counselling or to a specialist in fetal ultrasound.
Can all birth defects be detected by an 18-20 week ultrasound?
No. All women, regardless of their age, health or family history are at a 2-3 percent risk for having a baby born with a birth defect. While a prenatal ultrasound detects many serious birth defects, it does not detect all birth defects. In very rare cases, ultrasound may suggest a problem when one does not exist.
What if a problem is detected by ultrasound?
Sadly, for a few women, the ultrasound will detect a serious birth defect with their baby. Genetic counselling is available to provide information and support and, depending on the identified problem, discuss further pregnancy management options available.