Diagnosing amnionicity at 6 weeks of pregnancy with transvaginal three-dimensional ultrasonography: case report

Objective: To report a case of monochorionic, diamniotic twin pregnancy dia gnosed at 6 weeks of pregnancy with three-dimensional (3D) transvaginal son ography and to discuss the use of this diagnostic method in the evaluation of multifetal pregnancy in the first trimester. Design: Case report. Setting: University-based IVF program. Patient(s): A 30-year-old ovum recipient underwent ultrasonographic evaluat ion of a first-trimester twin pregnancy. Intervention(s): Two-dimensional (2D) and 3D transvaginal sonography. Main Outcome Measure(s): Accurate diagnosis of chorionicity and amnionicity . Result(s): Monoamniotic pregnancy and conjoined twinning could not be ruled out by using 2D transvaginal sonography at 6 weeks, because only one yolk sac (YS) and no membranes could be visualized, and the two embryos were clo sely positioned within one gestational sac. Applying 3D technique, two YSs and two separate embryos could clearly be observed, establishing the correc t diagnosis of a monochorionic, diamniotic pregnancy. Conclusion(s): The 3D transvaginal ultrasonography provides a quick and acc urate diagnostic modality for the evaluation of a first-trimester multiple gestation. (Fertil Steril(R) 1999;71:1161-4. (C) 1999 by American Society f or Reproductive Medicine.).