Ultrasound in Pregnancy
Ultrasound is high frequency, low-intensity sound waves that are directed into the body. Echoes from the
different surfaces of the baby and the pregnant person’s organs are reflected back to produce a picture.
Ultrasound is different from x-rays because it does not use radiation.
Why Is An Ultrasound Done?
An ultrasound can help to check on many aspects of a healthy pregnancy. This includes:
● Your estimated due date
● The number of babies
● The placement of the placenta
● Whether the baby ’s size is right for their age
● Whether there are concerns with your uterus, fallopian tubes or ovaries
It is your decision whether you have an ultrasound. All midwifery clients are offered at least one
ultrasound in pregnancy.
First Trimester “Dating” Ultrasound (7 - 13 weeks)
The Society of Obstetricians and Gynecologists of Canada (SOGC) recommends that all pregnant people
have an ultrasound in pregnancy. Every pregnant person should be offered a first trimester ultrasound to
provide accurate dating. A dating ultrasound may be done as early as 7 weeks, but is most accurate if done
between 9 and 11 weeks.
If you choose to have First Trimester Screening done, you will be offered another ultrasound, between 11 weeks
2 days to 13 weeks 3 days gestation, as part of the screening process. For more information, ask your midwife or visit:
https://prenatalscreeningontario.ca/en/pso/about-prenatal-screening/enhanced-first-trimester-screening-efts.aspx
“Routine” Second Trimester Ultrasound (18 – 22 weeks)
This ultrasound is called the “routine” second trimester screening ultrasound and is recommended for all
pregnant people. This examination:
● Can determine location of the placenta
● Can detect some serious abnormalities
● Can detect multiple pregnancies if not already done
● May confirm your due date, but is less accurate than first trimester ultrasound.
● May find treatable conditions, allowing for appropriate delivery planning
Ultrasound For Specific Reasons
Your midwife may recommend an ultrasound based on situations or circumstances that arise during your
pregnancy. Reasons an ultrasound may be recommended include:
● To confirm a pregnancy
● To confirm due date
● Suspicion of a multiple pregnancy
● Undetermined reasons for bleeding in pregnancy
● Concerns about the growth of the baby
● Confirming position of baby
● Confirming the continued wellbeing of a baby when pregnancy continues past the expected due date
What Will Happen During The Ultrasound?
Before you go for an ultrasound, you will get information on how to prepare and where to go. Sometimes, women
are told to arrive with a full bladder, but not so full it causes pain. This helps the sound waves travel better through
the skin and tissues. You may be asked to change from your own clothing into a medical gown.
The person who does the ultrasound is called an ultrasonographer. Once you are lying down on the examining table,
clear gel will be put on your skin. The gel allows the transducer to move easily on your skin and helps the sound waves
to transmit into your body. You may feel light pressure. An ultrasound exam takes about 30 minutes. If more tests are
needed, it could take longer.
Sometimes, the ultrasound must be done through the vagina (birth passage). A special kind of transducer is placed into
your vagina. Most women feel no pain during this type of ultrasound.
What Can An Ultrasound Find?
You should make sure you are fully informed about why you are having an ultrasound. It is an important way to learn
about problems. The results of an ultrasound may mean you will need to have more tests. Talk to your midwife before
you have an ultrasound to make an informed decision.
For most pregnant people, ultrasound assures them that their baby is healthy, and all is well. Sadly, for a few, the
ultrasound will find signs that not all is normal. Remember that this screen only indicates an increased chance for
concern and cannot tell you for sure if the baby does have a specific condition.
Your midwife will be told if the ultrasound shows any signs of abnormality. They will discuss this with you. You may be
referred to a centre that has expert doctors with experience in the field of fetal abnormalities.
Does A Normal Ultrasound Mean I Will Have A Healthy Baby?
Ultrasound can detect many, but not all, abnormalities. Finding an abnormality depends on many factors, including
the age and position of the baby, as well as the size and type of abnormality.
The clarity of the pictures depends on the ultrasound equipment and how well the ultrasound can pass through the
pregnant person’s abdomen. For example, ultrasound will be less clear when the person’s abdomen is thick or scarred.
Is An Ultrasound Safe?
Ultrasound has been used on pregnant people for many years. Studies continue to make sure ultrasound is safe.
So far, there is no reason to think that it harms pregnant people or their babies. As with all medical tests, the benefits
must always be greater than the risks. Health Canada regulates ultrasounds in Canada through two laws:
the Medical Devices Regulations of the Food and Drugs Act and the Radiation Emitting Devices Act.
This helps to ensure that ultrasounds are safe when used for medical reasons.
The Society of Obstetricians and Gynaecologists of Canada and Health Canada have produced guidelines on
diagnostic ultrasound. They state that an ultrasound. should not be used for any of these reasons:
● To have a picture of the baby, solely for non-medical reasons
● To learn the sex of the baby, solely for non-medical reasons
● For commercial use, such as trade shows or making videos of a baby
What About 3D/4D Ultrasound?
The Society of Obstetricians and Gynecologists of Canada (SOGC) and the Canadian Association of Radiologists
do not recommend 3D/4D ultrasound. When non-medical fetal ultrasound is performed, the maintenance of
technical safeguards, operator training, qualifications, expertise, and standards for infection control are no longer
ensured.
For more information on non-medical (3D/4D) ultrasound, visit:
https://www.pregnancyinfo.ca/?s=ultrasound
What Are the Benefits of Ultrasound?
Ultrasound can provide you with important medical information. Ultrasound must be used carefully to ensure that
you and your baby benefit from what it offers.
If your health-care provider recommends that you have an ultrasound,
make sure you know:
● Why it is recommended
● The risks that may be involved
● How it will be done
Disadvantages of Screening Ultrasound
Ultrasounds are not 100% accurate, some conditions may be missed. Even repeated scans cannot guarantee
there aren't any concerns.
There may be occurrences where the baby is suspected to have an abnormality or condition that they don’t
actually have.
News of even a minor abnormality may change parents’ experience of the pregnancy as they may focus on the
abnormality rather than the growing baby.
There may be findings on an ultrasound that are small or insignificant abnormalities. These often disappear later
in the pregnancy. Such findings can lead to unnecessary worry for parent(s) and more ultrasounds for a healthy baby.
To learn more about ultrasound, visit these websites:
Health Canada www.hc-sc.gc.ca
Canadian Society of Diagnostic Medical Sonographers www.sonographycanada.ca
