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Obstetric Ultrasound






Ultrasound (US) imaging, also called ultrasound scanning or sonography, is a method of obtaining images of internal organs by sending high-frequency sound waves into the body. The soundwave echoes are recorded and displayed as a real-time visual image. No ionizing radiation (x-ray) is involved in ultrasound imaging. Obstetric ultrasound refers to the specialized use of sound waves to visualize and thus determine the condition of a pregnant woman and her embryo or fetus.

General Electric Medical System’s new ultrasound technology that displays clinical images of the human body, allowing physicians and patients to see revolutionary “4D images,” is now available at all FMH Imaging locations. The fourth-dimension is real-time motion added to three-dimensional images. This technology dramatically expands diagnostic capabilities, therapy planning and ultrasound-guided minimally invasive diagnostic procedures such as biopsies.

Widely recognized for its clinical use in obstetrics and gynecology, 4D ultrasound with real-time motion is a new, powerful tool that can aid physicians studying the baby’s motion, behavior, the baby’s surface anatomy, and problems related to a woman’s uterus and ovaries.

What are some common uses of the procedure?

Obstetric ultrasound should be performed only when clinically indicated. Some indications may be:

  • To establish the presence of a living embryo/fetus.
  • To estimate fetal age.   
  • To diagnose congenital abnormalities.
  • To evaluate the position of the fetus.
  • To evaluate the position of the placenta.
  • To determine if there are multiple pregnancies.

How should I prepare for the procedure?

You should wear a loose fitting two-piece outfit for the examination. Only the lower abdominal area needs to be exposed during this procedure; consequently, a two-piece outfit will prevent you from having to readjust or remove all of your clothing.

If an ultrasound is required early in your pregnancy, you may be required to have a full bladder for the procedure. Air interferes with soundwaves, so if your bladder is distended, the air-filled bowel is pushed out of the way and an image of the uterus and embryo or fetus is obtained. About an hour and a half before the procedure, you should empty your bladder. You may be instructed to drink up to six glasses of water and avoid urinating until the procedure is completed. A full bladder is usually not necessary in the later stages of pregnancy.



What does the equipment look like?

The equipment consists of a transducer and a monitoring system. The transducer is a small hand-held device that resembles a microphone. The radiologist or sonographer spreads a lubricating gel on the area being examined and then presses this device firmly against the skin.

The ultrasound image is immediately visible on a nearby screen that looks much like a computer or television monitor. The radiologist or sonographer watches this screen during an examination and captures representative images for storage. Often, the patient is able to see it as well.




How does the procedure work?

Ultrasound imaging is based on the same principles involved in the sonar used by bats, ships at sea, and anglers with fish detectors. As a controlled sound bounces against objects, its echoing waves can be used to identify how far away the object is, how large it is, its shape and its internal consistency (fluid, solid or mixed).
The ultrasound transducer functions as both a loudspeaker (to create the sounds) and a microphone (to record them). For obstetric ultrasound, when the transducer is pressed against the skin, it directs a stream of inaudible, high-frequency sound waves into the lower abdomen. As the sound waves echo from the embryo or fetus and surrounding structures in the uterus, the sensitive microphone in the transducer records tiny changes in the sound's pitch and direction. These signature waves are instantly measured and displayed by a computer, which  in turn creates a real-time picture on the monitor.

The live images of the examination can be recorded on videotape. In addition, still frames of the moving picture are usually "frozen" to capture a series of images.
Doppler ultrasonography is the application of diagnostic ultrasound used to detect moving blood cells or other moving structures and measure their direction and speed of movement. The Doppler effect is used to evaluate movement by measuring changes in frequency of the echoes reflected from moving structures.
The movement of the embryo or fetus and fetal heart can be seen as an ongoing ultrasound "movie." Most ultrasound devices also have an audio component that processes the echoes produced by blood flowing through the fetal heart, blood vessels and umbilical cord. This sound can be made audible to human ears and has been described by patients as a "whooshing noise."

How is the procedure performed?

You will be asked to lie on your back or side. You will also be asked to expose your lower abdominal area. The sonographer or radiologist then spreads a warm water-soluble gel over your lower abdomen. This gel allows better transmission of the sound waves by making it easier to move the transducer over your abdomen and by sending the sound beam directly into the body without the interference from even a tiny amount of air on the skin. The transducer emits high-frequency sound waves as the sonographer or radiologist moves it over your abdomen. The transducer also detects the echoes that bounce off anatomic structures as reflections.

 Sometimes the radiologist determines that a transvaginal scan will need to be performed. Instead of a transducer being moved over your abdomen, the high-frequency waves will be emitted by a probe (transvaginal transducer) placed in the vagina. This technique often provides improved, more detailed images of the uterus and ovaries. It is especially useful in early pregnancy. With this approach the urinary bladder needs to be empty. Below is an example of an endovaginal transducer. Only two to three inches of the transducer are inserted into the vagina. The rest of the probe is a handle for use by the operator.

What will I experience during the procedure?

This is a painless procedure. There may be varying degrees of discomfort from pressure as the sonographer or radiologist guides the transducer over your abdomen, especially if you are required to have a full bladder. At times the sonographer may have to press more firmly to get closer to the embryo or fetus to better visualize the structure. This discomfort is temporary. Also, you may dislike the feeling of the water-soluble gel applied to your abdomen. With transvaginal scanning, there may be minimal discomfort as the probe is moved in the vagina.

Who interprets the results and how do I get them?

A radiologist, who is a physician experienced in obstetric ultrasound and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The patient receives ultrasound results from the referring physician who ordered the test. New technology also allows for distribution of diagnostic reports and referral images over the Internet at many facilities.



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