vasa praevia
Vasa previa refers to a situation where there are aberrant fetal vessels crossing over or in close proximity to the internal cervical os, ahead of the fetal presenting part. These vessels are within the amniotic membranes, without the support of the placenta. Vasa previa is a rare but potentially catastrophic cause of antepartum hemorrhage.
Pathology
Vasa previa can be of two types:
- type I (present in ~ 90% of cases with vasa previa ): abnormal fetal vessels connect a velamentous cord insertion with the main body of the placenta
- type II
- abnormal vessels connect portions of a bilobed placenta
- placenta with a succenturiate lobe: due to this association, vasa previa needs to be excluded in patients with variant placental morphology
These vessels are unsupported by Wharton jelly or placental tissue and are at risk of rupture during labor.
Epidemiology
Vasa previa occurs in 0.6 per 1000 pregnancies
Risk factors include:
- multiple gestations
- low lying placenta
- succenturiate lobe or bilobed placenta
- IVF pregnancy
Clinical presentation
Prior to rupture of the amniotic membrane during labor, compression of the vulnerable fetal blood vessels by the presenting part may lead to fetal heart decelerations and bradycardia.
However once ruptured, vasa previa will result in brisk vaginal bleeding with rapid fetal exsanguination.
Radiographic features
Antenatal ultrasound
Sonographic features are considered generally specific (~90%) .
The diagnosis is often made with transabdominal color Doppler sonography demonstrating flow within vessels which are seen overlying the internal cervical os. Non-Doppler (greyscale) images may suggest the diagnosis if there are echogenic parallel or circular lines within the placenta near the cervix.
Occasionally a transvaginal scan is required to better visualize aberrant vessels. Transvaginal ultrasound has a reported sensitivity of 100% and specificity of 99-99.8% when performed with color Doppler .
Treatment and prognosis
If recognized antenatally, vasa previa usually requires an elective cesarean section to avoid the risk of complications during vaginal delivery.
If recognized intrapartum, an emergency cesarean section is usually performed
Differential diagnosis
On antenatal ultrasound consider
- marginal sinus previa: where prominent maternal vessels are appreciated at the edge of the placenta
- funic presentation
Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu vasa praevia: