A fetal ultrasound, or sonogram, is an imaging technique that uses high-frequency sound waves to produce images of a baby in the uterus.
Fetal ultrasound images can help your health care provider evaluate your baby's growth and development and determine how your pregnancy is progressing. A fetal ultrasound might also give you the chance to study your baby's profile months before delivery. In some cases, fetal ultrasound is used to evaluate possible problems or confirm a diagnosis.
Fetal ultrasound may be done during the first trimester to confirm and date the pregnancy. Ultrasound is typically offered during the second trimester, when anatomic details are visible. If your baby's health needs to be monitored more closely, additional ultrasounds might be recommended.
First trimester ultrasound examination may be performed to evaluate presence, size, number and location of the pregnancy or for first-trimester sonographic genetic screening.
In the second semester ultrasound is typically performed to evaluate several features of the pregnancy, including fetal anatomy. The timing of this ultrasound may be altered in some women for reasons such as obesity or prior surgical incision at the scanning site, which could limit visualization of the fetus.
During the second and third trimesters, limited ultrasound evaluation may be indicated for evaluation of fetal growth, amniotic fluid, fetal well-being, confirmation of fetal presentation and placental abnormalities.
Here are some of the reasons your health care provider might use fetal ultrasound:
- Confirm the pregnancy and its location. Some embryos develop in the fallopian tube instead of in the uterus. A fetal ultrasound can help your health care provider detect a tubal (ectopic) pregnancy.
- Determine your baby's gestational age. Knowing the baby's age can help your health care provider determine your due date and track various milestones throughout your pregnancy.
- Confirm the number of babies. If your health care provider suspects a multiple pregnancy, an ultrasound might be done to confirm the number of babies.
- Evaluate your baby's growth. Your health care provider can use ultrasound to determine whether your baby is growing at a normal rate. Ultrasound can be used to monitor your baby's movement, breathing and heart rate as well.
- Study the placenta and amniotic fluid levels. The placenta provides your baby with vital nutrients and oxygen-rich blood. Too much or too little amniotic fluid — the fluid that surrounds the baby in the uterus during pregnancy — or complications with the placenta need special attention.
- Identify birth defects. An ultrasound can help your health care provider detect various birth defects.
- Investigate signs or symptoms. If you're bleeding or having other complications, an ultrasound might help your health care provider determine the cause.
- Perform other prenatal tests. Your health care provider might use ultrasound to guide needle placement during certain prenatal tests, such as amniocentesis or chorionic villus sampling.
- Determine fetal position before delivery. A C-section might be needed if the baby is in an abnormal position.
Fetal ultrasound should be performed only for valid medical reasons. Fetal ultrasound isn't recommended simply to determine a baby's sex. Similarly, fetal ultrasound isn't recommended solely for the purpose of producing keepsake videos or pictures.
If your health care provider doesn't suggest a fetal ultrasound but you'd like the reassurance the exam can provide, share your wishes as you work together to determine what's best for you and your baby.
Diagnostic ultrasound has been used during pregnancy for many years and is generally considered safe when used appropriately. The lowest amount of ultrasound energy that provides an accurate assessment should be used. Your obstetric provider and ultrasonographer have been trained in appropriate use of ultrasound energy.
Ultrasound should be requested only by a physician or licensed health care provider for medical reasons. The use of fetal ultrasound solely to create keepsake photos or videos isn't recommended.
Fetal ultrasound also has limitations. Fetal ultrasound might not detect all birth defects — or might incorrectly suggest a birth defect is present when it's not.
You might be asked to drink a certain amount of fluid or avoid urinating before a fetal ultrasound, depending on the type of ultrasound. When scheduling your ultrasound, ask your health care provider for specific instructions.
Also be aware that fetal ultrasound can be done through the vagina (transvaginal) or over the abdomen (transabdominal), depending on why it's being done or the stage of your pregnancy. If you're having a transabdominal ultrasound, consider wearing loosefitting clothing so that you can easily expose your abdomen.
There are two main types of fetal ultrasound exams:
- Transvaginal ultrasound. With this type of fetal ultrasound, a wand-like transducer is placed in your vagina to send out sound waves and gather the reflections. Transvaginal ultrasounds are used most often during early pregnancy, when the uterus and fallopian tubes are closer to the vagina than to the abdominal surface.
- Transabdominal ultrasound. A transabdominal fetal ultrasound is done by moving a transducer — a small plastic device that sends and receives sound waves — over your abdomen. This type of fetal ultrasound helps your health care provider determine your baby's gestational age and evaluate your baby's growth and development. The exam usually takes about 20 minutes.
Various other types of transabdominal ultrasounds are available, including:
- Specialized or targeted ultrasound. This type of fetal ultrasound targets a suspected problem and uses more sophisticated equipment than does a standard fetal ultrasound. The exam might take from 30 minutes to several hours.
- 3-D ultrasound. A 3-D fetal ultrasound can provide images of a baby with photo-quality details. This type of ultrasound is sometimes used to help health care providers evaluate a baby's growth and development, as well as detect facial abnormalities or neural tube defects.
- Doppler ultrasound. A Doppler ultrasound measures slight changes in the ultrasound waves as they bounce off moving objects, such as blood cells. A Doppler ultrasound can provide details about a baby's circulation.
- Fetal echocardiography. This type of fetal ultrasound provides a detailed picture of a baby's heart. It might be used to confirm or rule out a congenital heart defect.
During the exam
During a transabdominal fetal ultrasound, you'll recline on an exam table and expose your abdomen. Your health care provider or technician will apply a special gel to your abdomen. This will improve the conduction of sound waves and eliminate air between your skin and the transducer — the small plastic device that sends out sound waves and receives those that bounce back.
Your health care provider or technician will move the transducer back and forth over your abdomen. The sound waves reflected off your bones and other tissues will be converted into black-and-white or gray images on a monitor.
Your health care provider or technician will measure your baby's head, abdomen, thighbone and other structures. He or she might print or store certain images to document important structures. You'll likely be given copies of some of the images.
Depending on your baby's position and stage of development, you might be able to make out a face, hands and fingers, or arms and legs. Don't worry if you can't "see" your baby. Ultrasound images can be hard for an untrained observer to decipher. Ask your health care provider or technician to explain what's on the screen.
The procedure for other types of fetal ultrasound exams is similar. If you're having a transvaginal ultrasound, however, you'll be asked to change into a hospital gown or undress from the waist down. You'll recline on an exam table and place your feet in stirrups. Your health care provider or technician will place a lubricated transducer in your vagina rather than moving it across your abdomen.
After the exam
You can wipe off any residual gel or lubricant. If you had a full bladder during the ultrasound, you'll be able to urinate after the exam.
Typically, a fetal ultrasound offers reassurance that a baby is growing and developing normally. If your health care provider wants more details about your baby's health, he or she might recommend additional tests.
April 29, 2015
- Frequently asked questions. Special procedures FAQ025. Ultrasound. American College of Obstetrics and Gynecology. http://www.acog.org/~/media/For%20Patients/faq025.pdf?dmc=1&ts=20120731T1633444415. Accessed July 31, 2012.
- Shipp TD. Ultrasound examination in obstetrics and gynecology. http://www.uptodate.com/home/index.html. Accessed Aug. 1, 2012.
- Shipp TD. Basic principles and safety of diagnostic ultrasound in obstetrics and gynecology. http://www.uptodate.com/home/index.html. Accessed Aug. 1, 2012.
- Sfakianaki AK, et al. Routine prenatal ultrasonography as a screening tool. http://www.uptodate.com/home/index.html. Accessed Aug. 1, 2012.
- American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletins — Obstetrics. ACOG Practice Bulletin No. 101: Ultrasonography in pregnancy. Obstetrics & Gynecology. 2009;113:451. Reaffirmed 2014.
- AIUM practice guideline for ultrasonography in reproductive medicine. American Institute of Ultrasound in Medicine. http://www.aium.org/resources/guidelines/reproductiveMed.pdf. Accessed Aug. 1, 2012.
- Avoid fetal "keepsake" images, heartbeat monitors. U.S. Food and Drug Administration. http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095508.htm. Accessed Aug. 1, 2012.
- Frequently asked questions. Pregnancy FAQ155. Ectopic pregnancy. American College of Obstetrics and Gynecology. http://www.acog.org/~/media/For%20Patients/faq155.pdf?dmc=1&ts=20120801T1519144261. Accessed Aug. 1, 2012.
- Frequently asked questions. Pregnancy FAQ098. Special tests for monitoring fetal health. American College of Obstetrics and Gynecology. http://www.acog.org/~/media/For%20Patients/faq098.pdf?dmc=1&ts=20120801T1521295745. Accessed Aug. 1, 2012.
- Cope J. Prenatal sonographic diagnosis of fetal cardiac anomalies. http://www.uptodate/index. Accessed Aug. 1, 2012.
- Ghidini A. Chorionic villus sampling: Risks, complications, and techniques. www.uptodate.com/index. Accessed Aug. 1, 2012.
- Ghidini A. Diagnostic amniocentesis. http://www.uptodate.com/index. Accessed Aug. 3, 2012.
- Gibbs RS, et al. Danforth's Obstetrics and Gynecology. 10th ed. Philadelphia, Pa.: Wolters Kluwer Health Lippincott Williams & Wilkins; 2008. http://www.danforthsobgyn.com. Accessed Aug. 8, 2012.
- Harms RW (expert opinion). Mayo Clinic, Rochester, Minn. Aug. 14, 2012.
- ACR–ACOG–AIUM–SRU practice parameter for the performance of obstetrical ultrasound. Amended 2014. American College of Radiology. http://www.acr.org/~/media/ACR/Documents/PGTS/guidelines/US_Obstetrical.pdf. Accessed April 22, 2015.
- Fetal imaging: Executive Summary of a Joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Institute of Ultrasound in Medicine, American College of Obstetricians and Gynecologists, American College of Radiology, Society for Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging Workshop. Obstetrics and Gynecology. 2014;124:836.
- Ultrasound for fetal assessment in early pregnancy. Cochrane Database Systematic Review. 2010;(4):CD007058. Accessed April 22, 2015.
- Safety of ultrasonography in pregnancy: WHO systematic review of the literature and meta-analysis. Ultrasound Obstet Gynecol. 2009 May;33:599.