- 1 in 3,000 pregnancies.
- Umbilical vessels, unsupported by either the umbilical cord or placental tissue, traverse the fetal membranes of the lower segment above the cervix.
- Use of transvaginal ultrasound and color Doppler are necessary to make the diagnosis.
- Vasa previa usually occurs in association with velamentous cord insertion, bipartite placenta, or succenturiate lobe, where vessels run through the membranes to join the separate lobes.
- Risk factors are multiple pregnancies, IVF conceptions (1 in 300) and low lying placenta in the second trimester.
- Detailed ultrasound examination, including transvaginal sonography with color Doppler.
- Serial scans every 2 weeks after 26 weeks to monitor cervical length. If there is cervical shortening (<25 mm) hospitalization should be considered.
- Delivery by cesarean section at 34 to 36 weeks, depending on cervical length.
- Fetal death: >60% if not diagnosed prenatally and <3% if diagnosed prenatally.
- No increased risk of recurrence.