Fetal ultrasound

Definition

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 may also give you the chance to study your baby's profile and watch his or her tiny heart beat months before delivery. In some cases, fetal ultrasound is used to evaluate possible problems or confirm a diagnosis.

Fetal ultrasound is often done during the first trimester to confirm and date the pregnancy and the second trimester — between 18 and 20 weeks — when anatomic details are visible. If your baby's health needs to be monitored more closely, ultrasounds may be repeated throughout the pregnancy.

Why it's done

A fetal ultrasound can be done at any point during pregnancy. Your health care provider may use a fetal ultrasound to:

• 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 and treat 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 may be done to resolve the question.
• 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. The placenta provides your baby with vital nutrients and oxygen-rich blood. Any problems with the placenta need special attention.
• Identify fetal abnormalities. An ultrasound can help your health care provider detect various congenital abnormalities. An early diagnosis may lead to early interventions that help save or improve a baby's life.
• Investigate signs or symptoms. If you're bleeding or having other complications, an ultrasound may help your health care provider determine the cause.
• Perform other prenatal tests. Your health care provider may use ultrasound to guide needle placement during certain prenatal tests, such as checking a sample of amniotic fluid for specific genetic problems (amniocentesis) or testing a sample of the placenta for genetic abnormalities (chorionic villus sampling).
• Determine fetal position before delivery. A C-section may be needed if the baby is in an abnormal position.

Fetal ultrasound isn't recommended simply to determine a baby's sex — but it may be a bonus for curious parents when an ultrasound is done for medical reasons. 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.

Risks

Routine fetal ultrasounds are considered safe for both mother and baby. Improper use of fetal ultrasound, however, can't be considered entirely risk-free. Although researchers haven't noted any adverse effects of fetal ultrasound on children followed for several years after birth, caution remains important.

Fetal ultrasound also has limitations. Fetal ultrasound may not detect all birth defects — or may incorrectly suggest a birth defect is present when it's not.

How you prepare

You may be asked to drink a certain amount of fluid before the ultrasound or refrain from urinating before the exam, depending on the specific type of fetal ultrasound. When scheduling your ultrasound, ask your health care provider for specific instructions.

What you can expect

Various types of fetal ultrasound exams are available, including:

• Standard ultrasound. A standard fetal ultrasound is done by moving a transducer — a small plastic device that sends and receives sound waves — over your abdomen. A standard fetal ultrasound helps your health care provider determine your baby's gestational age and evaluate your baby's growth and development. A standard fetal ultrasound usually takes about 20 minutes.
• Transvaginal ultrasound. With this type of fetal ultrasound, a slender 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.
• 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 may take from 30 minutes to several hours.
• Three-dimensional (3-D) ultrasound. A 3-D fetal ultrasound can provide images of a baby with photo-quality details. This type of ultrasound is used in select medical centers 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 may be used to confirm or rule out a congenital heart defect.

During the exam
During a standard fetal ultrasound, your health care provider or technician will apply a special gel to your abdomen as you recline on an exam table. The gel improves conduction of sound waves and eliminates 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 may 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 may 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 are 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, the transducer will be placed in your vagina rather than moved across your abdomen.

After the exam
If you had a full bladder during the ultrasound, you'll be able to urinate after the exam.

Results

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 may recommend additional tests.