Objective: To evaluate the safety of transvaginal ultrasonography in the diagnosis of placenta previa by determining whether the angle between the cervix and the vaginal probe is sufficient for alignment of the probe with the cervix.
Methods: The angle between the axis of the cervix and that of the vaginal probe (the axis of the vagina) was measured from copies of the transvaginal ultrasound examinations of 18 patients with documented placenta previa past 20 weeks' gestation. The measurements were compared with those of gestationally matched controls without placenta previa.
Results: The mean angles were 63.8 degrees and 67.5 degrees, with minimum angles of 44 degrees and 48 degrees for the placenta previa and control groups, respectively. The values were not statistically different.
Conclusion: These findings strengthen the previously undocumented presumption that the angle between the cervix and vaginal probe is sufficient to prevent the probe from inadvertently slipping into the cervix. Therefore, this study supports the safety of transvaginal sonography in diagnosing and monitoring patients with known placenta previa.