Health Encyclopedia - Test
A pregnancy ultrasound is an imaging test that uses sound waves to create a picture of how a baby is developing in the womb. It is also used to check the female pelvic organs during pregnancy.
Pregnancy sonogram; Obstetric ultrasonography; Obstetric sonogram; Ultrasound - pregnancy
How the Test is Performed
To have the procedure:
- You will lie on your back on an exam table.
- The person performing the test will spread a clear, water-based gel on your belly and pelvis area. A hand-held probe will then be moved the area. The gel helps the probe transmit sound waves.
- These waves bounce off the body structures, including the developing baby, to create a picture on the ultrasound machine.
In some cases, a pregnancy ultrasound may be done by placing the probe into the vagina.
How to Prepare for the Test
You will need to have a full bladder to get the best ultrasound image. You may be asked to drink 2 to 3 glasses of liquid an hour before the test. Do not urinate before the procedure.
How the Test will Feel
There may be some discomfort from pressure on the full bladder. The conducting gel may feel slightly cold and wet. You will not feel the ultrasound waves.
Why the Test is Performed
An ultrasound may be done to determine if there is a problem with the pregnancy, how far along the pregnancy is, or to take measurements and screen for potential problems.
Talk to your health care provider to determine the most appropriate scanning schedule for you.
A pregnancy ultrasound may be done during the first 12 weeks of pregnancy to:
- Confirm a normal pregnancy
- Determine the baby's age
- Look for problems, such as ectopic pregnancies or the chances for a miscarriage
- Determine the baby's heart rate
- Look for multiple pregnancies (twins, triplets, etc.)
- Identify problems of the placenta, uterus, cervix, and ovaries
- Look for findings that might indicate an increased risk for Down syndrome
A pregnancy ultrasound may also be done in the second and third trimesters to:
- Determine the baby's age, growth, position, and sometimes gender
- Identify any problems with how the fetus is developing
- Look for twins, triplets, etc.
- Look at the placenta, amniotic fluid, and pelvis
Some centers are now performing a pregnancy ultrasound around 9 - 13 weeks of pregnancy to look for signs of Down syndrome or other problems in the developing baby. This test is often combined with blood tests to improve the accuracy of results.
How many ultrasounds you will need depends on whether a previous scan or blood test has detected problems that require follow-up testing.
The developing baby, placenta, amniotic fluid, and surrounding structures appear normal for the gestational age.
Note: Normal results may vary slightly. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal ultrasound results may be due to some of the following conditions:
- Birth defects
- Ectopic pregnancy
- Poor growth of a baby while in the mother's womb
- Multiple pregnancies
- Problems with the baby's position in the womb
- Problems with the placenta, including placenta previa and placental abruption
- Too little amniotic fluid
- Too much amniotic fluid (polyhydramnios)
- Tumors of pregnancy, including gestational trophoblastic disease
- Other problems with the ovaries, uterus, and remaining pelvic structures
Current ultrasound techniques appear to be safe. Ultrasound does not involve radiation.
Richards DS. Obstetrical ultrasound: Imaging, dating, and growth. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Saunders Elsevier; 2012:chap 9.
Taval VS. Emergency ultrasound. In Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Mosby Elsevier; 2013:chap 196.
Reviewed By: Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, WA; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.