Objective: To explore the positive significance of using prenatal B-ultrasound in diagnosing fetal abnormalities. Methods: A total of 200 pregnant women who visited Shaanxi Provincial People’s Hospital between January 2023 and January 2024 were recruited as the research subjects. All pregnant women received prenatal examinations. A retrospective analysis was carried out to analyze the positive significance of prenatal B-ultrasound examination in the diagnosis of fetal abnormalities. Results: Prenatal B-ultrasound examination detected 10 cases of fetal abnormalities, with a detection rate of 5.00%. When compared with the postnatal examination results of 5.50%, the difference was insignificant (P > 0.05). Moreover, comparing the fetal limb abnormalities and cardiovascular abnormalities in prenatal B-ultrasound examination and postnatal examination, one case of congenital heart disease was missed in the prenatal B-ultrasound examination, and the others were consistent with the postnatal examination results, with a coincidence rate of 90.91%, indicating a high compliance rate. Conclusion: Fetal abnormalities have a great impact on mothers, babies, and families, and it is particularly important to strengthen diagnosis during this process. Prenatal B-ultrasound examination can improve the accuracy of diagnosis of fetal abnormalities and can be promoted in clinical practice as a basis for screening fetal abnormalities.