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One of the main purposes of an obstetrical ultrasound is to confirm that you are in fact pregnant. They can be performed at any time during your pregnancy, but the earliest that an embryo is usually visible with a heartbeat is at about six weeks gestation.

During the first trimester of pregnancy (under 14 weeks), your doctor will often request an early obstetrical ultrasound, sometimes called a dating ultrasound. It’s best performed at, or after, seven weeks and will confirm whether you are pregnant, as well as the number of babies you’re expecting.

To estimate the gestational age of your baby and thus your due date, the sonographer will measure your baby from top to bottom, recording the crown-rump-length (CRL). At seven weeks your baby is usually about the size of a peanut and measures around 10 mm long. During your exam, your baby’s well-being will also be assessed by seeing and documenting your baby’s heartbeat. Your uterus and surrounding organs will also be examined.

In your first trimester your doctor may also request a nuchal translucency ultrasound to help determine your baby’s risk of having one of several genetic conditions. During this exam, your sonographer will take a specific measurement of the skin thickness at the back of the neck, and it’s performed between 11 weeks and 13 weeks, 6 days.

During your second trimester, at 18 to 20 weeks pregnant, your doctor will request a 40-minute detailed obstetrical ultrasound. Sometimes called an anatomic ultrasound, this exam involves your sonographer taking many measurements of your baby from head-to-toe to determine how well your baby is growing. He or she will capture images to view the development of your baby’s brain, face, heart, spine, chest, major organs, arms, legs, feet, and hands.

Your sonographer will also examine the position of your placenta, the vessels in the umbilical cord, the amount of amniotic fluid, and your cervix, uterus, ovaries, and bladder for abnormalities. It’s also during this exam when the gender of your baby may first be visible – if the baby is in a good position.

Throughout the rest of your pregnancy you may have one or more follow-up ultrasounds, called a biophysical profile and growth ultrasound. The purpose of these exams is to monitor your baby’s growth and well-being. Your baby’s heart rate, breathing, movements, muscle tone, and amniotic fluid will be assessed, as well as fetal size. Sometimes babies grow bigger or smaller than expected, so physicians may request ultrasounds to help ensure a healthy pregnancy.


Ultrasound imaging is noninvasive and doesn’t use radiation. It has been used to evaluate pregnancy for nearly four decades and there has been no evidence of harm to the patient, embryo, or fetus. However, it should only be performed when medically necessary.

Ultrasound imaging provides a clear picture of the uterus and provides much information about your pregnancy. It may be temporarily uncomfortable, but shouldn’t be painful. And while they can offer reassurance about your baby’s health, we do understand that they can also cause anxiety.


Most pregnancies have a gestation period of 40 weeks, which means you could have four or more ultrasounds during that time. These exams help your doctor monitor the health of you and your baby and inform care decisions.

Once your doctor has identified the need for an ultrasound, your doctor’s office may book an appointment for you, or provide you with a number to call to book your appointment. You will also be given a requisition form and preparation instructions for your exam.

For early, nuchal translucency, and detailed obstetrical ultrasounds, you will need to arrive for your exam with a full bladder. A full bladder helps the sonographer to see your cervix and moves the uterus up so we are better able to see your baby.

Once in the exam room you may be asked to change into a gown and then be positioned by one of our compassionate and experienced sonographers. A warm, unscented, hypo-allergenic ultrasound gel will be applied to your abdomen, and your sonographer will move the transducer around the front and side of your abdomen to gather images. You may experience mild pressure while the sonographer takes the images.

Obstetrical ultrasounds generally take between 25 and 40 minutes, but this may vary depending on how much your baby moves and its position. Your sonographer will do her or his best to ensure your comfort while also acquiring accurate measurements and the best possible images for you and your doctor.

Measuring your baby during any obstetrical ultrasound can be challenging and requires concentration, so your sonographer will usually show you images of your baby towards the end of your exam. We can also save images of your baby on a complimentary USB, to share with family and friends. You would need to speak with one of our clinic receptionists for more details.

Mayfair Diagnostics has 12 locations across Calgary which provide ultrasound services, as well as one in Regina. For more information about our clinic locations and services, please visit our clinic location pages, or you can drop by the nearest clinic.


Mayo Clinic Staff (2018) “Biophysical profile.” Accessed July 11, 2019.

Radiological Society of North America (2019) “Obstetric Ultrasound.” Accessed July 11, 2019.

Society of Obstetricians and Gynaecologists of Canada (2009) “Content of a Complete Routine Second Trimester Obstetrical Ultrasound Examination and Report.” Journal of Obstetrics and Gynaecology Canada. Mar. 31(3): 272-75.

Society of Obstetricians and Gynaecologists of Canada (2019) “Routine ultrasound.” Accessed July 11, 2019.

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