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Pregnancy ultrasound

Definition

A pregnancy ultrasound is an imaging test that uses sound waves to see how a baby is developing in the womb. It is also used to check the female pelvic organs during pregnancy.

Ultrasound

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Ultrasound

Alternative Names

Pregnancy sonogram; Obstetric ultrasonography; Obstetric sonogram; Ultrasound - pregnancy

How the test is performed

You will lie down for the procedure. The person performing the test places a clear, water-based gel on your belly and pelvis area and then moves a hand-held probe over 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. For information on this procedure, see transvaginal ultrasound.

How to prepare for the test

A full bladder is necessary to get a good picture. Therefore, you may be asked to drink 2 to 3 glasses of liquid an hour before the test. You should 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

Some doctors order an ultrasound when they think there may be a problem with the pregnancy or if there is a question about how far along the pregnancy is. Others advocate screening ultrasounds. You should consult your health care provider to determine the most appropriate scanning schedule for you.

A pregnancy ultrasound may be done in the first trimester 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

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 developmental problems
  • Look for multiple pregnancies (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 developmental problems in the developing baby. This test is often combined with blood tests to improve the accuracy of results.

The total number of scans will depend on whether a previous scan or blood test has detected problems that require follow-up testing.

Normal Values

The developing baby, placenta, amniotic fluid, and surrounding structures are normal in appearance and appropriate 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
  • Intrauterine growth restriction
  • Multiple pregnancies
  • Miscarriage
  • 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

What the risks are

Current ultrasound techniques appear to be safe, and there is no documented risk to women or their developing babies. Ultrasound does not involve radiation, such as that used when taking an x-ray.

References

Richards DS. Ultrasound for pregnancy dating, growth, and the diagnosis of fetal malformations. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 9.

Taval VS, Glass CM. Emergency ultrasound. In: Marx JA, ed. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 197.


Review Date: 2/21/2010
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Redmond, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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