The Obstetric Ultrasound Examination: Guidelines

Practice Guidelines: Overview

This chapter reviews the components of the standard obstetrical (OB) ultrasound examination, as delineated in the ACR-ACOG-AIUM-SRU Practice Parameter for the Performance of Obstetrical Ultrasound. The practice parameter was developed through the collaboration of the American College of Radiology (ACR), American College of Obstetrics and Gynecology (ACOG), American Institute of Ultrasound in Medicine (AIUM), and the Society of Radiologists in Ultrasound (SRU). The practice parameter is updated at least every 5 years. The material that follows describes the OB ultrasound guidelines based on the revision adopted in 2013.

The practice parameter describes the standard OB ultrasound examination. It is subdivided into specifications for first-trimester evaluation and second- or third-trimester evaluation. Two additional types of ultrasound studies are cited as well: a limited examination and a specialized examination. The limited examination does not incorporate all the components of the standard OB sonogram, but instead is tailored to address specific questions. The limited examination may be performed in emergencies or in nonemergent situations when there is a specific question to address (e.g., to determine fetal presentation in a patient in labor, assess cardiac activity, evaluate fetal growth, or assess the cervix). In most situations a limited examination is considered appropriate only when a prior complete ultrasound examination is on record.

A specialized examination (often termed a detailed examination) is performed when the pregnancy is at increased risk of abnormalities or when pathology is suspected based on a limited or standard examination. A specialized examination typically includes a more exhaustive assessment of the fetus than the standard examination. Other specialized exami­nations include fetal Doppler, biophysical profile, and fetal echocardiography. The content of limited and specialized examinations varies according to the particular situation and is not covered by the ACR-ACOG-AIUM-SRU Practice Param­eter for the Performance of Obstetrical Ultrasound. There is, however, a separate guideline for fetal echocardiography that was developed by the Fetal Echocardiography Task Force through the AIUM in collaboration with the ACOG, the Society for Maternal-Fetal Medicine, and the American Society of Echocardiography and endorsed by the ACR.

In addition to describing the components of the standard OB ultrasound examination, the practice parameter covers clinical indications for OB ultrasound and equipment specifications and addresses fetal safety. The ALARA (i.e., as low as reasonably achievable) concept of performing examinations in a manner that ensures ultrasound exposure is minimized should be followed. Ultrasound exposure should be monitored using the thermal index for soft tissue before 10 weeks and the thermal index for bone from 10 weeks to the end of pregnancy. Consistent with the ALARA principle, M-mode imaging should be used to document heart rate, rather than spectral Doppler, which is associated with higher levels of ultrasound exposure. The practice parameter also provides space for the collaborating organizations to insert society-specific recommendations regarding qualifications and responsibilities of personnel, written requests for the examination, documentation, quality control and improvement, safety, infection control, and patient education, as these sections vary depending on the organization.

The remainder of this chapter elaborates on the discussions in the “Imaging Parameters” sections of the practice parameter for the standard OB ultrasound examination. The “Comment” sections in the practice parameter are also included because they are an integral component of the document, covering crucial information. Specifications for the first-trimester examination are described separately from those for the second or third trimester. All “ Comment ” sections (shown in italics) and bolded text are direct quotes from the practice parameter.