Note: This guideline has been updated. The National Guideline Clearinghouse (NGC) is working to update this summary. The recommendations that follow are based on the previous version of the guideline.
The grades of evidence (I-III) and levels of recommendation (A-C) are defined at the end of the "Major Recommendations" field.
Conclusions
- Ultrasound examination is an accurate method of determining gestational age, fetal number, viability, and placental location. Gestational age is most accurately determined in the first half of pregnancy.
- The ability of ultrasonography to diagnose major fetal anomalies is well established.
- The diagnosis of fetal growth abnormalities with ultrasonography is not precise.
- Ultrasonography is safe for the fetus when used appropriately.
- Specific indications are the best basis for the use of ultrasonography in pregnancy.
- The optimal timing for a single ultrasound examination in the absence of specific indications for a first-trimester examination is at 16-20 weeks of gestation.
Summary of Recommendations
The following recommendation is based on limited or inconsistent scientific evidence (Level B):
- Serial ultrasonograms to determine the rate of growth should be obtained approximately every 2 to 4 weeks.
The following recommendations are based primarily on consensus and expert opinion (Level C):
- Casual use of ultrasonography, especially during pregnancy, should be avoided.
- Before an ultrasound examination is performed, patients should be counseled about the limitations of ultrasonography for diagnosis.
Definitions:
Grades of Evidence
I: Evidence obtained from at least one properly designed randomized controlled trial.
II-1: Evidence obtained from well-designed controlled trials without randomization.
II-2: Evidence obtained from well-designed cohort or case–control analytic studies, preferably from more than one center or research group.
II-3: Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled experiments also could be regarded as this type of evidence.
III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.
Levels of Recommendations
Level A — Recommendations are based on good and consistent scientific evidence.
Level B — Recommendations are based on limited or inconsistent scientific evidence.
Level C — Recommendations are based primarily on consensus and expert opinion.