A case of twin reversed arterial perfusion (TRAP) sequence was diagnosed at
12 weeks' gestation using transvaginal color Doppler ultrasound, which dem
onstrated the presence of retrograde perfusion in the umbilical artery of t
he abnormal twin. Ultrasound imaging showed a monochorionic-diamniotic twin
pregnancy with an inappropiately grown second twin, the morphological eval
uation of which revealed an abnormal cephalic pole with acrania, diffuse su
bcutaneous edema and the presence of cardiac activity in an abnormal heart
with a single chamber.