Ultrasound: Sonogram

An ultrasound exam is a procedure that uses high-frequency sound waves to scan a woman's abdomen and pelvic cavity, creating a picture (sonogram) of the baby and placenta. Although the terms ultrasound and sonogram are technically different, they are used interchangeably and reference the same exam.

What types of ultrasound are there?

There are basically seven different ultrasound exams but the principle process is the same. The different types of procedures include:

Transvaginal Scans: Specially designed probe transducers are used inside the vagina to generate sonogram images. Most often used during the early stages of pregnancy.
Standard Ultrasound: Traditional ultrasound exam which uses a transducer to generate 2-D images of the developing fetus.

Advanced Ultrasound: This exam is similar to the standard ultrasound, but the exam targets a suspected problem and uses more sophisticated equipment.

Doppler Ultrasound: This imaging procedure measures slight changes in the frequency of the ultrasound waves as they bounce off moving objects, such as blood cells.

3-D Ultrasound: Uses specially designed probes and software to generate 3-D images of the developing fetus.

4-D or Dynamic 3-D Ultrasound: Uses specially designed scanners to look at the face and movements of the baby prior to delivery.

Fetal Echocardiography: Uses ultrasound waves to assess the baby's heart anatomy and function. This is used to help assess suspected congenital heart defects.

How is an ultrasound performed?

The traditional ultrasound procedure involves placing gel on your abdomen to work as a conductor for the sound waves. Your health care provider uses a transducer to produce sound waves into the uterus. The sound waves bounce off bones and tissue returning back to the transducer to generate black and white images of the fetus.

When are ultrasounds performed?

Ultrasounds may be performed at any point during pregnancy, and the results are seen immediately on a monitor during the procedure. Transvaginal scans may be used early in pregnancy to diagnosis potential ectopic or molar pregnancies.

Pulsed Doppler ultrasounds may pick up a heart beat as early as six weeks, but is clearly visible at seven weeks.

A specific recommendation for the number of ultrasound procedures does not exist. Some health care providers will schedule an ultrasound exam every seven weeks whereas others will schedule an ultrasound early in the pregnancy between 6 to 10 weeks, and then again around 20 weeks. Additional ultrasounds will be ordered separately if your healthcare provider suspects an abnormality or problem related to your pregnancy.

What does the ultrasound look for?

Ultrasounds are diagnostic procedures that detect or aid in the detection of abnormalities and conditions related to pregnancy. Ultrasounds are usually combined with other tests, such as triple tests, amniocentesis, or chorionic villus sampling, to validate a diagnosis. An ultrasound exam is used throughout pregnancy for the following reasons:

  • First Trimester:
    • Confirm viable pregnancy
    • Confirm heartbeat
    • Measure the crown-rump length or gestational age
    • Confirm molar or ectopic pregnancies
    • Assess abnormal gestation
  • Second Trimester:
    • Diagnose fetal malformation
      • Weeks 13-14 for characteristics of potential Down syndrome
      • Weeks 18-20 for congenital malformations
    • Structural abnormalities
    • Confirm multiple pregnancies
    • Verify dates and growth
    • Confirm intrauterine death
    • Identify hydramnios or oligohydramnios – excessive or reduced levels of amniotic fluid
    • Determine gender of the baby
  • Third Trimester:
    • Identify placental location
    • Confirm intrauterine death
    • Observe fetal presentation
    • Observe fetal movements
    • Identify uterine and pelvic abnormalities of the mother during pregnancy

What are the risks and side effects to the mother or baby?

The ultrasound is a non-invasive exam which poses no risks to the mother or developing fetus.

Answers to common questions related to an ultrasound exam

If an ultrasound is done at 6 to 7 weeks and a heartbeat is not detected, does that mean there is a problem?
No it does not mean there is a problem. The heartbeat may not be detected for reasons that include: tipped uterus, larger abdomen, or inaccurate dating with last menstrual period. Heartbeats are best detected with transvaginal ultrasounds early in pregnancy. Concern typically develops if there is no fetal heart activity in an embryo with a crown-rump length greater than 5mm. During a six week ultrasound exam, your healthcare provider will begin to be concerned if there is no gestational sac.

How accurate are ultrasounds in calculating gestational age?
Your healthcare provider will use hormone levels in your blood, the date of your last menstrual period and results from the ultrasound to generate an estimated gestational age. However, variations in each woman's cycle and each pregnancy may hinder the accuracy of generating an accurate gestational age. Physician's use an ultrasound to get an estimated delivery date to base the timing of your prenatal care, and normally will not change the original estimated gestational age.

Why do some healthcare providers schedule ultrasounds differently?
Scheduling an ultrasound every seven weeks is an average for most physicians. If there are any questions regarding gestational age, possible complications or health risks, then more ultrasounds may be scheduled.

Some healthcare providers may only schedule two sonograms, one between 6 to 10 weeks and the second around 20 weeks, because most of the information needed for effective prenatal care may be retrieved during these exams.

How accurate are ultrasounds in determining the conception date to determine paternity?
Your healthcare provider will use hormone levels in your blood, the date of your last menstrual period and results from an ultrasound to generate an expected date of conception. However, the many differences in each woman's cycle may hinder the accuracy of generating an accurate date of conception. The viability of sperm varies as well, which means that intercourse three to five days prior to ovulation may result in conception. Ultrasound dating of conception is not reliable for determining paternity unless the encounters in question are at least two weeks apart.

When can an ultrasound determine the sex of the baby?
The gender of the baby can begin to be determined between 18 to 20 weeks. Accuracy is improved when the observation is made of male genitals because they are more distinct. However, even when these have been observed, the birth can reveal something different!

Are ultrasounds a necessary part of prenatal care?
Ultrasound procedures are part of routine prenatal care and provide your healthcare provider with valuable insights for giving you the highest level of care. As noted above, ultrasounds enable your healthcare provider to confirm normal development as well as diagnose potential problems. Because there are no risks to you or the developing baby, there are no reasons not to use ultrasound technologies.

Reprinted with permission from American Pregnancy Association