Main associations for vasa previa:
(1) abnormal placentation
(2) abnormal insertion of the umbilical cord
(3) abnormal fertility
(3) abnormalities felt on physical examination
Abnormal placentation:
(1) bilobed placenta (2 separate disks of approximately equal size)
(2) succenturiate placenta (accessory disk)
(3) 3 or more plates (rare)
(4) low lying placenta (near the cervical canal)
Abnormal insertion of the umbilical cord:
(1) velamentous insertion
(2) marginal insertion
Abnormal fertility:
(1) multiple pregnancies (twins, triplets, etc.)
(2) pregnancy secondary to in vitro fertilization
Abnormal physical examination:
(1) palpable umbilical cord
(2) palpable structure thought to represent an amniotic band
The presence of one or more of these findings should prompt transvaginal Doppler ultrasonography.
