Diagnostic Techniques and Criteria for First-Trimester Conjoined Twin Documentation: A Review of the Literature Illustrated by Three Recent Cases

Objectives Conjoined twins are rare. High-quality imaging techniques are essential for proper first-trimester diagnosis. Technological development leads to new imaging techniques such as 3-dimensional virtual embryoscopy. The aim of this review was to explore imaging techniques used in the first-trimester diagnosis of conjoined twins and provide a systematic diagnostic table for making this diagnosis. Design A PubMed literature search was performed using the terms ultrasound, Doppler, MRI, and CT combined with first-trimester and conjoined twins. Three recent cases at our department are reviewed and examined additionally using 3-dimensional virtual embryoscopy. Results The different types of conjoined twins are summarized in a table for practical use during ultrasound examination. In evaluating conjoined twins, 2-dimensional ultrasound is the criterion standard. Three-dimensional and Doppler ultrasounds add anatomical and prognostic information. Virtual embryoscopy imaging reveals additional findings in our 3 cases not seen with routine 2-dimensionalultrasound examination. Conclusions Each case of conjoined twins is unique and should be evaluated with the best possible imaging techniques. Three-dimensional and Doppler ultrasound should be added to the systematic diagnostic evaluation of conjoined twins. Virtual embryoscopy imaging may contribute to earlier, more appropriate counseling and management of these pregnancies. Target Audience: Obstetricians and gynecologists, family physicians Learning Objectives: After completing this CME activity, physicians should be better able to differentiate between the different types of conjoined twins and their prognosis, compare the different imaging techniques used for the evaluation of conjoined twins to decide whether additional diagnostic imaging techniques are useful in an individual case, and evaluate complex cases, such as conjoined twins, using new imaging techniques.