Ultrasounds: What You Should Know

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Ultrasounds are often used during pregnancy for everything from accurately predicting your due date to looking for birth defects to just checking in on the size and development of your growing baby. Here's a look at what types of ultrasounds are available, how they work, and what they mean for you and your baby.

Ultrasounds Defined

Ultrasound tests use sound waves above the range of human hearing to create an image of organs within the body. The sound waves are reflected off of your internal body structures and back to the ultrasound machine. These "bounce back" sound waves are then analyzed by computer and turned into pictures.

This method of imaging results in less clear pictures than X-rays, CAT scans, or MRIs; however, there is no radiation risk with ultrasound and no confirmed adverse effects on the fetus or mother from diagnostic ultrasound examinations in pregnancy.

Different Types of Ultrasounds

These are the different types of ultrasound exams:

• Limited exams are focused studies used to answer specific questions about the fetus, mother, or both. This exam is often used when you go to your doctor or the hospital with an urgent problem related to your pregnancy.
• Basic exams are performed to survey for obvious malformations of the fetus and to estimate fetal age, the amount of amniotic fluid present, location of the placenta, and other concerns. These are the kind of exams you would likely receive in your doctor's office or in the hospital as part of a routine evaluation. They are typically performed at 18 to 20 weeks of pregnancy.
• Comprehensive exams provide a more in-depth look at the fetus when there is reason to suspect something is wrong with the fetus or mother. They include a detailed examination that is often done as a response to an abnormal screening test such as the alpha-fetoprotein screen. This is sometimes called a Level II or Level III ultrasound. Technical difficulties and the need to image many different areas of the fetus may extend the length of this exam to 30 or more minutes.