Prenatal ultrasonography is a common procedure. In the United States, the Centers for Disease Control and Prevention reported that a prenatal ultrasound examination was performed in 67 percent of live births in 2002 . The percent was higher in white women than in black women. Whether all obstetrical patients should undergo ultrasound screening and whether such screening improves pregnancy outcome is controversial. Currently, the American College of Obstetricians and Gynecologists (ACOG), the American Institute for Ultrasound in Medicine (AIUM), and the American College of Radiology (ACR) support the use of ultrasound when there is a specific medical indication and advises against casual use of ultrasonography during pregnancy [2-5]. ACOG also stated that the benefits and limitations of ultrasonography should be discussed with all patients, and performance of the procedure is reasonable in patients who request it.
Many other countries have developed local guidelines for the practice of prenatal ultrasonography and most offer at least one mid-trimester ultrasound examination as part of standard prenatal care, although worldwide obstetric practice varies.
An evidence-based discussion of the application of ultrasound to an unselected obstetric population as a screening tool will be presented here. The use of prenatal ultrasonography for specific obstetrical indications is reviewed separately. (See "Ultrasound examination in obstetrics and gynecology".)
OBJECTIVES OF PRENATAL SCREENING ULTRASOUND
The primary objective of routine fetal ultrasound examination is to obtain information that will enable delivery of optimal antenatal care and thus the best possible outcomes for mother and fetus . The following information is obtained: (See "Ultrasound examination in obstetrics and gynecology".)
- Fetal viability
- Gestational age and expected date of delivery
- Number of fetuses. Chorionicity should be determined in multiple gestations.
- Fetal biometry
- Fetal survey to detect congenital anomalies, including signs suggestive of aneuploidy
- Assessment of amniotic fluid volume
- Placental location (2nd trimester)