Prenatal Ultrasound

At some time during your pregnancy, your physician or nurse practitioner may ask you to schedule an ultrasound exam. This prenatal test will be done at one of our clinics or at the outpatient radiology department at Abbott Northwestern Hospital. This screening test is offered to women who are at low risk of having a baby with a structural abnormality. Your physician will have discussed your level of risk with you.

What is an ultrasound test?

An ultrasound test (also called a sonogram) uses high-frequency sound waves that are safe for both you and your fetus. The test enables the doctor to see precise pictures of the fetus’s soft tissue. Sound waves are sent through a special computer mouse–like device called a transducer, which is rolled back and forth on the surface of your abdomen or introduced into the vagina. The sound waves are converted into photographic images or videos of the fetus, which are recorded and displayed on a monitor screen.

What are some reasons you may need a prenatal ultrasound?

An ultrasound during pregnancy tells your physician more information about the health of your fetus:

  • your estimated due date (fetal age)
  • number of fetuses
  • fetal location and position in the uterus
  • location of placenta
  • amount of amniotic fluid
  • fetal movement and rate of growth
  • breathing and heart rate of fetus
  • possible birth defects
  • sex determination (not always accurate)

What happens during a routine ultrasound? 

When a transvaginal ultrasound is ordered, you will be asked to undress from the waist down and given a gown or sheet to wear during the procedure. You will lie on the exam table as you would for a pelvic exam. The technician will cover the vaginal probe with a condom-like sheath and then apply ultrasound gel before inserting the probe into your vagina. You may feel some pressure in your vagina during this exam.

For a transabdominal ultrasound, you will lie down on an exam table with shirt raised up to expose your abdomen. The ultrasound technician will apply a special gel to your abdomen. The gel helps sharpen the images. The technician will move the transducer around on the gel to pick up the image. The gel may at first feel slightly cool and moist to the touch, and moving the transducer will put a small amount of pressure on the abdomen.

Depending on where you get your ultrasound (our clinic or at the hospital), you will be given preliminary results soon after the procedure is done. Images will also be reviewed more carefully by a doctor in our clinic or an ultrasound radiologist at the hospital later that day for a final reading.  

How do you prepare for an ultrasound test?

With very early ultrasounds, a transvaginal ultrasound is used. You will be asked to empty your bladder before this test is done.

Ultrasounds done after the first trimester are most often transabdominal. To obtain the best pictures of the fetus inside the uterus, your physician may ask that you have a full bladder. Having a full bladder pushes parts of the intestine out of the way, allowing the uterus to move upward against the abdominal wall. The ultrasound transducer then has a virtually unobstructed view of the fetus and uterus. To ensure a full bladder for the ultrasound, your doctor may instruct you to drink several glasses of water during the 2 hours before the test. Having a full bladder during an ultrasound may be slightly uncomfortable.

In some circumstances, both a transabdominal and a transvaginal ultrasound will need to be performed. The transabdominal ultrasound will be performed first, and you will need to have a full bladder. After the transabdominal ultrasound is completed, you will be asked to empty your bladder before the transvaginal ultrasound is performed.

As always, please ask your doctor about which preparation is needed.

When is a screening ultrasound generally scheduled?

Screening ultrasounds are usually scheduled between 19 and 20 weeks of pregnancy. At this time the fetus will be big enough for important structures to be seen (e.g., two kidneys, four chambers in the heart, etc.) and for the gender to be identified.

When is the earliest time to schedule a sonogram for age of fetus?

The developing fetus cannot be seen before 6 weeks gestational age (4 weeks after date of conception). If you are unsure of the date of conception, or are having abdominal pain or bleeding and know that you are pregnant, your physician will discuss the reasons and timing for doing an early ultrasound.