Sirenomelia sequence: first-trimester diagnosis with both two- and three-dimensional sonography.

Objective: To describe the sonographic findings of sirenomelia during the first trimester on both two-dimensional sonography with color Doppler imaging and three-dimensional sonography.
Methods: Two cases of sirenomelia in primiparous patients with histories of infertility are described. The diagnosis was made on the basis of two-dimensional sonography, and three-dimensional sonography was used to further characterize the findings.
Results: Both fetuses had size-date discrepancies, increased nuchal translucency, large intra-abdominal vessels, and 2-vessel umbilical cords. Both pregnancies were terminated by dilation and curettage after the patients viewed the three-dimensional pictures of the fetuses.
Conclusions: During the first trimester of pregnancy, rare and lethal anomalies can be diagnosed with a high degree of confidence if a thorough, age-dependent anatomic survey of the fetus is performed.