The grades of evidence (I-III) and levels of recommendation (A-C) are defined at the end of the "Major Recommendations" field.
The following conclusions are based on good and consistent evidence (Level A):
- 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.
- Ultrasonography can be used in the diagnosis of many major fetal anomalies.
- Ultrasonography is safe for the fetus when used appropriately.
The following conclusions are based on limited or inconsistent evidence (Level B):
- Ultrasonography is helpful in detecting fetal growth disturbances.
- Ultrasonography can detect abnormalities in amniotic fluid volume.
The following conclusion and recommendation are based primarily on consensus and expert opinion (Level C):
- The optimal timing for a single ultrasound examination in the absence of specific indications for a first trimester examination is at 18–20 weeks of gestation.
- The benefits and limitations of ultrasonography should be discussed with all patients.
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.