The Role of Contrast-to-noise Ratio in Assessing the Quality of Obstetric Ultrasound: Subjective Approach and the Influence of Maternal and Obstetric Factors.

Background: This study aimed to compare sonographer assessment of scan quality using contrast-to-noise ratio (CNR) for obstetric ultrasound images to identify the maternal and obstetric factors that could affect scan quality. Methods: This retrospective study included 187 consecutive ultrasound scans at 18 weeks of gestation, 205 fetuses, and 565 ultrasound images. Ultrasound scans were performed by a single operator using a General Electric ultrasound machine and a 2-7-MHz RM6C convex probe with the same ultrasound settings. Two independent, blinded sonographers rated the contrast and noise of the abdominal perimeter, four-chamber, and sagittal spine views on a scale of 1-3. The sonographer scores were categorized as poor, fair, good, or excellent, respectively. Patient scans were considered unsatisfactory if they had at least one poor CNR; good if they had more than three CNRs classified as good or excellent; and acceptable otherwise. Results: Interobserver agreement for CNR was moderate to good with 0.53< intraclass correlation coefficient 0.68; Conclusion: We demonstrated good interoperator reproducibility of CNR. Maternal obesity was the main factor affecting fetal ultrasound quality.