Antepartum Management of Vasa Previa
Vasa previa occurs when fetal blood vessels, that are unprotected by the umbilical cord or placenta, run through the amniotic membranes and traverse the cervix. Two types of vasa previa occur: type 1 is associated with a velamentous cord insertion, and type II with succenturiate or multilobed placentae. The exact frequency of vasa previa is difficult to determine, but it probably occurs in 1 in 1,500 to 5,000 pregnancies. Fetal hemorrhage, exsanguination, or even death may result with rupture of vasa previa vessels whether spontaneous or during artificial rupture of membranes. Vasa previa can be successfully managed through appropriate diagnosis, preparation and readiness for surgery.
Diagnosis has been improved with grayscale ultrasonography and color Doppler. Screening for and establishing the diagnosis is important as antenatal, compared to intrapartum, diagnosis is associated with improved maternal and fetal/neonatal outcomes. Debate exists regarding whether screening should be performed routinely in all pregnancies. Certain conditions associated with vasa previa such as low-lying placenta, multi-fetal gestation, IVF or presence of an accessory lobe of the placenta should raise suspicion and warrant further investigation. Routine ultrasound evaluation of the placenta and lower uterine segment permits detection in the majority of cases. The following algorithm can facilitate diagnosis in asymptomatic women:
- At mid-trimester ultrasound, routinely determine placental location and relationship of placenta to internal cervical os, and document placental cord insertion site.
- If placenta previa or low-lying placenta diagnosed at mid-trimester ultrasound, perform a follow-up ultrasound at 32 weeks gestation (or sooner as needed). Perform transvaginal ultrasonography with color and pulsed doppler to rule out vasa previa even if previa/low-lying placenta resolved as risk for vasa previa is increased.
- Diagnosis is confirmed when an arterial vessel is visualized over the cervix (either directly over or in close proximity). The course of the vessel should be evaluated and with color Doppler will demonstrate a rate consistent with the fetal heart rate.
When vasa previa is suspected on antenatal ultrasound, it has a specificity of 99%.
Once the diagnosis is established, successful management includes pelvic rest, hospitalization, and preterm delivery. While hospitalization does not guarantee a good outcome, it does improve the chance of intact fetal survival compared to vasa previa rupturing outside of a hospital. For this reason, experts recommend corticosteroid administration between 28-32 weeks if clinical indications do not merit it earlier, consideration of preterm hospitalization between 30-34 weeks until delivery, and scheduled delivery at 34-37 weeks. Delivery timing needs to balance fetal well-being and pulmonary maturity against risks of spontaneous labor, spontaneous membrane rupture, and fetal exsanguination. In addition to these risks, there is also concern for cord compression and fetal compromise. Elective cesarean delivery around 35 weeks may be optimal.
The addition of amniocentesis for fetal lung maturity poses its own risks and does not appear to add value. Some cases of vasa previa due to a succenturiate lobe (type II) may be treated antenatally with laser ablation of the vessels, but this procedure may not be available in many locations.
Swank ML, Garita TJ, Maurel K, et al, Obstetrix Collaborative Research Network. Vasa previa: diagnosis and management. Am J Obstet Gynecol. 2016 Aug;215(2):223.e1-6. doi: 10.1016/j.ajog.2016.02.044. Epub 2016 Mar 2.
Gagnon R. No. 231-Guidelines for the Management of Vasa Previa. J Obstet Gynaecol Can. 2017 Oct;39(10):e415-e421. doi: 10.1016/j.jogc.2017.08.016.
Sinkey RG, Odibo AO, Dashe JS. Diagnosis and management of vasa previa. Society for Maternal–Fetal Medicine Consult Series #37. Am J Obstet Gynecol. 2015 Nov;213(5):615-9. doi: 10.1016/j.ajog.2015.08.031. Epub 2015 Aug 18.
Initial Approval: October 2011, Revised: May 2018. Reaffirmed November 2019
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