By the numbers

Vasa Previa Risks

How often vasa previa occurs, which findings are most often present when it does, and how much prenatal diagnosis changes the outcome for the baby. Every figure comes from a published systematic review, listed at the bottom of the page.

Share this page
1 · How common

About 1 in 1,700 to 2,200 pregnancies

Two systematic reviews give similar estimates.

0.46 per 1,000 deliveries

428 pregnancies with vasa previa among 1,027,918 deliveries in 21 studies.

Pavalagantharajah et al., Am J Obstet Gynecol MFM 2020 [1]
0.60 per 1,000 pregnancies

Mean incidence from 10 cohort studies in a review of 569,410 patients with 325 cases.

Ruiter et al., BJOG 2016 [2]
2 · Risk factors

Risk factors ranked by how often they are present

Share of pregnancies with vasa previa that had each finding. The dark bar is the pooled estimate; the bracket shows the 95% confidence interval. A pregnancy can have more than one.

  1. 1
    Low-lying placentaIncludes placenta previa in the second trimester
    61.5%
  2. 2
    Velamentous cord insertion
    52.2%
  3. 3
    Bilobed or succenturiate lobed placenta
    33.3%
  4. 4
    In vitro fertilization
    26.4%
  5. 5
    Multiple gestation
    8.9%
Pooled prevalence, Pavalagantharajah et al. 2020 [1]
~83%of vasa previa cases had one or more risk indicators [2]
OR 10.96for vasa previa after assisted reproduction (95% CI 2.94 to 40.89), from a single study [3]
5risk indicators identified across 13 studies, including low cord insertion on first-trimester ultrasound [2]

These percentages describe pregnancies that already have vasa previa. They show which findings to look for, not the chance that a pregnancy with one of these findings has vasa previa.

3 · Outcomes

Prenatal diagnosis changes the outcome

Seven studies included vasa previa both with and without a diagnosis before birth.

Perinatal survival

Diagnosed before birth
98.6%
Not diagnosed
72.1%

Survival without hypoxic injury

Diagnosed before birth
96.7%
Not diagnosed
28.1%
Zhang et al., Ultrasound Obstet Gynecol 2021 [4]
25×higher odds of perinatal death without a prenatal diagnosis (OR 25.39, 95% CI 7.93 to 81.31) [4]
50×higher odds of hypoxic morbidity without a prenatal diagnosis (OR 50.09, 95% CI 17.33 to 144.79) [4]
81.9%of pregnancies with vasa previa delivered preterm, in descriptive studies [5]

Compared with controls, vasa previa carried a higher risk of preterm delivery (RR 3.36, 95% CI 2.76 to 4.09) and of perinatal death (RR 4.52, 95% CI 2.77 to 7.39) [5]. Use the Pathway tool to see which ultrasound a pregnancy needs.

Share this page

Send these numbers to a colleague or patient

Shares only the link to this page.

Email Text message WhatsApp Facebook LinkedIn X Threads Bluesky Reddit

Sources

  1. Pavalagantharajah S, Villani LA, D'Souza R. Vasa previa and associated risk factors: a systematic review and meta-analysis. Am J Obstet Gynecol MFM. 2020;2(3):100117. doi:10.1016/j.ajogmf.2020.100117
  2. Ruiter L, Kok N, Limpens J, et al. Incidence of and risk indicators for vasa praevia: a systematic review. BJOG. 2016;123(8):1278-1287. doi:10.1111/1471-0528.13829
  3. Matsuzaki S, Ueda Y, Matsuzaki S, et al. Assisted reproductive technique and abnormal cord insertion: a systematic review and meta-analysis. Biomedicines. 2022;10(7):1722. doi:10.3390/biomedicines10071722
  4. Zhang W, Geris S, Al-Emara N, et al. Perinatal outcome of pregnancies with prenatal diagnosis of vasa previa: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2021;57(5):710-719. doi:10.1002/uog.22166
  5. Vahanian SA, Lavery JA, Ananth CV, Vintzileos A. Placental implantation abnormalities and risk of preterm delivery: a systematic review and metaanalysis. Am J Obstet Gynecol. 2015;213(4 Suppl):S78-S90. doi:10.1016/j.ajog.2015.05.058