A comparison of transvaginal and abdominal ultrasound in visualizing the first trimester conceptus.

Ultrasound visualization of the first trimester embryo was compared using abdominal and transvaginal sonography. The parameters evaluated included the ability to obtain biometry, the ability to visualize detailed internal anatomy, and a subjective assessment of the overall image clarity. In 120 patients studied, transvaginal sonography was superior to abdominal sonography in obtaining biometric measurements in 51 cases (43%) and for visualizing internal anatomy in 45 cases (38%); also the image clarity of transvaginal sonography was subjectively better in 75 cases (63%). Vaginal sonography was superior to abdominal sonography in gestations less than or equal to 10 weeks, in obese patients, and in patients with retroverted uteri. The major difficulty encountered with transvaginal sonography was the limited maneuverability of the probe to generate specific views. Vaginal sonography can be a valuable tool in imaging the first trimester fetus, complementing, not replacing, abdominal sonography.