Vasa previa occurs in pregnancy when one of the membrane vessels extends down to the level of the internal cervical os, ahead of the fetal presenting part and unsupported by the placenta tissue or umbilical cord. The rupture of the vessels might happen spontaneously or artificially and frequently results in fetal exsanguination and demise. Ultrasound prenatal diagnosis is highly important as it allows the identification of patients at risk, thus an elective cesarean can be performed before rupture the membranes. We report a case of vasa previa diagnosed through color Doppler mode in the 30th week of gestation, emphasizing the contribution of three-dimensional power Doppler to the adequate mapping of aberrant vessels, which greatly contributed to the success of the perinatal result.