Obstetrical US

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

• To establish the presence of a living embryo/fetus.
• To estimate the age of the pregnancy.
• 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.
• To determine the amount of amniotic fluid around the fetus.
• To check for opening or shortening of the cervix or mouth of the womb.

What to expect with your 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 ordered by your clinician early in your pregnancy, you may be instructed to have a full bladder for the procedure. Air interferes with sound waves, 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 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 not necessary in most cases, especially after the first two to three months of pregnancy. The radiologist or sonographer may elect to examine an early pregnancy by means of transvaginal ultrasound. This requires an empty urinary bladder. You should ask for instructions when you make your appointment.

Preparing for your procedure

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 and detects the echoes that bounce off anatomic structures.

Sometimes the radiologist determines that an endovaginal scan will need to be performed. Instead of a transducer being moved over your abdomen, the high-frequency waves will be emitted by a transducer placed in the vagina. Only two to three inches of the transducer are inserted into the vagina. The rest of the transducer is a handle for use by the operator. 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.

The obstetric ultrasound examination takes about 20 minutes.