Vasa previa

Last revised by Maulik S Patel on 6 Aug 2023

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.

Vasa previa occurs in 0.6 per 1000 pregnancies 11.

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.

Vasa previa can be of two types:

These vessels are unsupported by Wharton jelly or placental tissue and are at risk of rupture during labor.

Sonographic features are considered generally specific (~90%) 2.

The diagnosis is often made with transabdominal color Doppler sonography demonstrating flow within vessels that are seen overlying the internal cervical os. 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 12.

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.

On antenatal ultrasound consider:

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