Fetal Ultrasound

HealthLinkBC File Number: 
Last Updated: 
September 2016

Your health care provider may request that you have one or more fetal ultrasound scans during your pregnancy. These ultrasound scans provide important medical information that will help you and your health care provider create the best care plan for you and your baby.

What is a fetal ultrasound?

A fetal ultrasound scan is a painless medical procedure which is ordered by your physician, midwife, or nurse practitioner. It uses sound waves to make a live picture of your baby in the womb that can be seen on a monitor. Ultrasounds are done with a hand held instrument called a transducer. The transducer gives off sound waves which cannot be heard by the human ear. The sound waves bounce off the baby and then the ultrasound machine detects the sound waves and turns them into an image.

These images are used to determine the health and well-being of your baby. A doctor, with expertise in interpreting ultrasound, reviews the images and sends a written report to your health care provider who requested the ultrasound.

How is the fetal ultrasound done?

There are 2 ways a fetal ultrasound can be done:

  1. A transabdominal ultrasound is done by moving a transducer over your belly.
  2. An endovaginal (EV), or transvaginal, ultrasound is done by gently placing a narrow transducer in your vagina.

The endovaginal scan provides a better view of the lower part of your uterus. However, you may choose not to have this type of ultrasound scan even if it is recommended by your health care provider.

Most often, medical ultrasounds are 2 dimensional (2D), which means a flat image rather than a 3 dimensional (3D) image.

Are fetal ultrasounds safe?

Medical 2D ultrasound has been used in pregnancy for over 40 years. Many studies have been done to determine if a medical ultrasound is safe and there is no clear evidence to suggest it is dangerous for either you or your baby. Ultrasound is not an X-ray and does not use ionizing radiation.

All ultrasound scans are ordered by a doctor, midwife, or nurse practitioner, and must be done by properly trained people who have special knowledge and skill in fetal ultrasound.

What can I do to prepare for my appointment?

When you book your ultrasound, you will be given instructions on how to prepare for your appointment. For example, you may be asked to come to your ultrasound appointment with a full bladder.

At what stage of my pregnancy should I have a fetal ultrasound?

An ultrasound scan may be ordered by your physician midwife, or nurse practitioner at any time during your pregnancy, based on your medical needs. Most often it will be recommended that you have an ultrasound during your first and second trimesters. The scan will show different information depending on when the ultrasound is performed during your pregnancy, and the reason your health care provider has requested it.

What information will a fetal ultrasound provide?

In general a fetal ultrasound scan may:

  • look at the size and growth of your baby;
  • look to see if your baby is developing normally or if there are any major physical concerns;
  • check on the amount of amniotic fluid around your baby;
  • show what position your baby is in; and
  • help investigate any concerns your health care provider might have about your uterus, ovaries, placenta or cervix.

First Trimester (up to 14 weeks)

An ultrasound done during the first trimester is the best time to:

  • determine how far along you are in your pregnancy;
  • estimate your due date; and
  • help determine if there is more than one baby and if they share a placenta and/or the amniotic sac (the bag of fluid inside the womb where a baby develops).

Some women are eligible for an ultrasound to perform a nuchal translucency (NT) measurement as part of prenatal genetic screening. This type of ultrasound may be done along with blood tests to determine your baby's chance of having Down syndrome (DS), Trisomy 18 or an open neural tube defect. Please talk to your health care provider to learn more about your prenatal genetic screening options.

Second Trimester (15 to 27 weeks)

An ultrasound between 18 and 20 weeks into your pregnancy is often called the detailed or level 2 ultrasound. It is the best time to look at the anatomy of your baby and try to see if there are any birth defects. The shape and size of your baby’s structures are examined, but the ultrasound cannot always tell how well those structures are working.

The best time to look for ultrasound “markers” is 18 to 20 weeks into your pregnancy. Markers are not birth defects. They are most often normal variations in growth and development and when they are seen, might suggest a more serious problem such as Down syndrome or Trisomy 18. When a “marker” is seen, you may be offered further testing and information by your health care provider. Most babies that have an ultrasound “marker” are completely healthy and well.

Having a completely normal ultrasound does not guarantee a completely healthy baby.

Third Trimester (after 27 weeks)

You may be asked to have one or more third trimester ultrasounds if your health care provider is concerned about:

  • your baby's size, growth or position;
  • the amount of amniotic fluid around your baby;
  • the location of your placenta; or
  • the length of your cervix.

Can I find out the sex of my baby?

During the 18 to 20 week second trimester scan, the genitals (sex organs) of your baby are usually examined as part of the detailed look at your baby’s anatomy. If the position of your baby allows for the genitalia to be clearly seen, the sex (male or female) will be listed on the final report and the health care provider who ordered the test can tell you, if you wish to know.

The sonographer performing the ultrasound is not able to give you detailed information about what they see on the ultrasound, including the sex of your baby. The results of the scan can only be obtained from your physician, midwife or nurse practitioner. If you do not want to know the sex of your baby, let your health care provider and the sonographer know.

Be aware that the ultrasound is not always correct in determining the sex of your baby.

An ultrasound exam will not be booked, or a routine exam extended, for the sole purpose of identifying the sex of the baby.

What factors might limit the information that I get from an ultrasound?

There are certain factors that may limit what information you get from your ultrasound. They include:

  • if the pregnant woman is overweight or obese;
  • a very small or big baby;
  • a low amount of fluid around the baby; and
  • what position the baby is in.

Can I get pictures from the ultrasound?

Some clinics that perform medically indicated 2D ultrasound scans do provide photos. When you check in for your ultrasound, ask about this possibility, and the cost.

Some clinics offer and perform 3D ultrasounds for keepsake or entertainment purposes only. Providing medical information is not the main purpose of these ultrasounds.

Ultrasound scans, including fetal ultrasounds, are medical procedures and should only be used when there is a medical reason to do so. Health Canada, the Society of Obstetricians of Canada, the Canadian Association of Radiologists, the College of Physicians and Surgeons of BC, and the International Society of Ultrasound and Gynecology recommend ultrasounds for medical purposes only and not for non-medical (keepsake) purposes.

For More Information

For more information on fetal ultrasounds, visit:

For information on prenatal genetic screening, visit Perinatal Services BC - Prenatal Genetic Screening Program www.perinatalservicesbc.ca/our-services/screening-programs/prenatal-genetic-screening-program.

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