Transvaginal sonographic fetal axis determination in early second trimester

Objective: Correct prenatal determination of the fetal right/left axis is essential for the diagnosis of fetal malformations, in particular congenital heart anomalies. A reliable method of transabdominal echocardiographic assessment of the fetal situs in the late second trimester was established. We aimed to determine the validity of the transvaginal approach to assess fetal axis. Method: The study group consisted of 108 consecutive women in the second trimester of a singleton pregnancy, undergoing elective transvaginal anatomy scans. All had undergone previous transabdominal echocardiography to establish fetal axis. The same technique was used to assess the fetal axis during the transvaginal study, and the findings were compared. Results: There was total agreement in fetal axis determination between transabdominal and transvaginal scans in all cases. The accuracy of the transvaginal study was not affected by maternal obesity, fetal position or the presence of cardiac malformation (in one case). Conclusion: Transvaginal ultrasonography is the reliable and accurate means of determining the fetal axis.