Obstetrical (Pregnancy) Ultrasound

Obstetrical Ultrasound Preparation - click for PDFObstetrical Ultrasound Thumbnail Image

For patient safety, patients exceeding the posted weight restrictions will not be done at London X-Ray Associates. The weight limit for all Ultrasound exams is 350 lbs.


Ultrasound uses sound, not x-rays, to produce images. A probe placed on the surface of the body sends a thin, high-frequency sound beam (above the range that humans can hear) into the body. The sound bounces off of structures within the body and back to the probe. A computer is able to construct images based on the time required for these echoes to return. An obstetrical ultrasound examines both the mother and baby to ensure that the baby is developing normally and there are no complications. The time to perform an obstetrical ultrasound varies with the stage of pregnancy as well as the baby's position and amount of movement. Exam time could be 10 to 45 minutes.

Common reasons for an Obstetrical (Pregnancy) Ultrasound

Some of the more common reasons why your doctor would order an obstetrical ultrasound would include:

      • Confirming pregnancy
      • Confirming that the baby is alive
      • Making sure the pregnancy is normally located within the uterus
      • Determining the number of babies
      • Confirming the age of the baby and its due date
      • Assessing the baby - checking for abnormalities
      • Monitoring growth and estimated weight
      • Investigating abnormal bleeding or fluid loss
      • Assessing placenta location and fetal position
      • Integrated Prenatal Screening (IPS / Nuchal Sonolucency)
        For more information contact the Medical Genetics Program of Southwestern Ontario at L.H.S.C.
        (Medical Genetics Program of Southwestern Ontario - click for website)

Who should not have an Ultrasound of Pregnancy?

Ultrasound is an extremely safe procedure and there are very few conditions that would prevent it from being performed. Since a probe must be placed in contact with the skin, ultrasound may not be possible in those with open sores or large open wounds over the area of interest.

Only one ultrasound is necessary during a normal, uncomplicated pregnancy.

How do I prepare for the test?

Obstetrical ultrasound uses the full bladder as a "window" to see into the pelvis. You must finish 4 glasses of water (32 ounces/~ 1 litre) at least one hour prior to the procedure. Your bladder must be full. Do not empty your bladder prior to the examination.

Who performs the examination?

An ultrasound technologist (a person trained to take ultrasound images) performs the examination. At London X-ray Associates, all of our technologists have met and maintain registration standards with the international governing body called the American Registry of Diagnostic Medical Sonographers.

What happens during the examination?

After registering with a receptionist, you may be asked to change into a gown and remove your top and pants or skirt. Initially only the patient will be taken into the examination room. Family members and friends will be asked to wait a short time in the waiting room. This allows the technologist to focus on the exam and the required pictures with minimal distraction. Family members and friends are welcome to be present at the end of the obstetrical scan.

You will be taken to the examination room which contains an ultrasound machine and an examination table. You will be asked to lie on the table on your back. Your lower abdomen will need to be exposed. The technologist will apply a gel to your skin to improve contact with the probe. The technologist will move the probe to various positions over your lower abdomen, taking several ultrasound pictures. The number of pictures and length of exam varies with the stage of pregnancy. The technologist may ask you to change position and empty your bladder during the examination.

At the end of the examination the technologist will print some images on paper - "baby pictures" which you may take home with you.

What can I expect after the examination?
Ultrasound of pregnancy has no after-effects and you should be able to return to activities of daily living.

What are the risks of the procedure?
Ultrasound is an extremely safe procedure that does not expose the body to x-rays. Ultrasound transmits very small quantities of sound energy into the body but this produces no known harmful effects when standard techniques are used.

Who interprets the results and how do I get them?
The images are interpreted by one of our radiologists (a doctor who is trained to interpret x-rays and other medical images) and the results are sent to the doctor who ordered the ultrasound by courier or fax.

Arrangements to discuss the results of the ultrasound can be made with the doctor who ordered the test.

Is it a boy or girl?
Sometimes, but not always, it is possible to get a good enough look to determine the gender of the baby. If well seen, the reporting radiologist will include the sex in the report going to the doctor. You may ask your doctor if gender is included in the report. The technologist is not able to give this information directly to the patient.

Are childcare (baby sitting) services available while I have my exam?
No childcare services are available. Please prearrange the following:
Adult supervision in the waiting room must be provided at all times for children while you, the caregiver, are having your exam completed. London X-Ray Associates staff will not be able to provide any childcare needs. We ask that all children be supervised by an adult, other than the patient, while at London X-Ray Associates.
Thank you.