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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Pregnancy ultrasound

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

Last reviewed: February 21, 2010.

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.

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:

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

  1. 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.
  2. 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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What works?

  • Routine ultrasound in late pregnancy (after 24 weeks' gestation)Routine ultrasound in late pregnancy (after 24 weeks' gestation)
    Ultrasound can be used in late pregnancy to assess the baby's condition when there are complications, but carrying out scans on all women is controversial. Scans can be used in late pregnancy to detect problems which may not otherwise be apparent, such as abnormalities in the placenta, in the fluid surrounding the baby, or in the baby's growth. If such problems are identified this may lead to changes in care and improved outcome for babies. At the same time, screening all women may mean that interventions are increased without benefit to mothers or babies. Scans are popular, but women may not fully understand the purpose of their scan and may be either falsely reassured or unprepared for adverse findings. Based on existing evidence, routine ultrasound, after 24 weeks gestation, in low‐risk or unselected women does not provide any benefit for mother or baby. Eight studies that randomised 27,024 women to screening or a control group (no or selective ultrasound, or ultrasound with concealed results) contributed to the review. The quality of trials was satisfactory. There were no differences between groups in the rates of women having additional scans, antenatal admissions, preterm delivery, induction of labour, or instrumental deliveries although the rate of caesarean section increased slightly with screening. For babies, birthweight, condition at birth, interventions such as resuscitation, and admission to special care were similar between groups. Infant survival, with or without congenital abnormalities, was no different with and without routine screening, and childhood development at eight to nine years was similar in the three trials that measured it. None of the trials reported on psychological effects for mothers of routine ultrasound in late pregnancy.
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Figures

  • Ultrasound in pregnancy.
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    Ultrasound, normal fetus - foot.
    Ultrasound, normal fetus - head measurements.
    Ultrasound, normal fetus - heartbeat.
    Ultrasound, ventricular septal defect - heartbeat.
    Ultrasound, normal fetus - arms and legs.
    Ultrasound, normal relaxed placenta.
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    Ultrasound, normal fetus - spine and ribs.
    Ultrasound, color - normal umbilical cord.
    Ultrasound, normal fetus - ventricles of brain.

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