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Vasa praevia (vasa previa AE) is an obstetric complication in which fetal blood vessels cross or run near the external orifice of the uterus. These vessels are at risk of rupture when the supporting membranes rupture, as they are unsupported by the umbilical cord or placental tissue.^[1]

Etiology/Pathophysiology

Vasa previa is present when fetal vessels traverse the fetal membranes over the internal cervical os. These vessels may be from either a velamentous insertion of the umbilical cord or may be joining an accessory (succenturiate) placental lobe to the main disk of the placenta. If these fetal vessels rupture the bleeding is from the fetoplacental circulation, and fetal exsanguination will rapidly occur, leading to fetal death.

Risk Factors

Vasa previa is seen more commonly with velamentous insertion of the umbilical cord, accessory placental lobes (succenturiate or bilobate placenta), multiple gestation, IVF pregnancy. In IVF pregnancies incidences as high as one in 300 have been reported.The reasons for this association are not clear, but disturbed orientation of the blastocyst at implantation, vanishing embryos and the increased frequency of placental morphological variations in in vitro fertilisation pregnancies have all been postulated ^[2]

Diagnosis

The classic triad of the vasa praevia is: membrane rupture, painless vaginal bleeding and fetal bradycardia.
This is rarely confirmed before delivery but may be suspected when antenatal sono-gram with color-flow Doppler reveals a vessel crossing the membranes over the internal cervical os.^[3]^[4]
The diagnosis is usually confirmed after delivery on examination of the placenta and fetal membranes^{[citation needed]}.
Alkali denaturation test detects the presence of fetal hemoglobin in vaginal blood, as fetal hemoglobin is resistant to denaturation in presence of 1% NaOH.
Also detection of fetal hemoglobin in vaginal bleeding is diagnostic.

Treatment

Immediate treatment with an emergency caesarean delivery is usually indicated.^[5]^[6]

References

^ Yasmine Derbala, MD; Frantisek Grochal, MD; Philippe Jeanty, MD, PhD (2007). "Vasa previa". Journal of Prenatal Medicine 2007 1 (1): 2–13. Full text
^ http://www.rcog.org.uk/files/rcog-corp/GTG27PlacentaPraeviaJanuary2011.pdf
^ Lijoi A, Brady J (2003). "Vasa previa diagnosis and management.". J Am Board Fam Pract 16 (6): 543–8. doi:10.3122/jabfm.16.6.543. PMID 14963081. Full text
^ Lee W, Lee V, Kirk J, Sloan C, Smith R, Comstock C (2000). "Vasa previa: prenatal diagnosis, natural evolution, and clinical outcome.". Obstet Gynecol 95 (4): 572–6. doi:10.1016/S0029-7844(99)00600-6. PMID 10725492.
^ Bhide A, Thilaganathan B (2004). "Recent advances in the management of placenta previa.". Curr Opin Obstet Gynecol 16 (6): 447–51. doi:10.1097/00001703-200412000-00002. PMID 15534438.
^ Oyelese Y, Smulian J (2006). "Placenta previa, placenta accreta, and vasa previa.". Obstet Gynecol 107 (4): 927–41. doi:10.1097/01.AOG.0000207559.15715.98. PMID 16582134.

7. Textbook of Obstetrics by D.C. Dutta 7th edition, page 259

External links

International Vasa Previa Foundation

UpToDate Contents

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1. 臍帯卵膜付着と前置血管 velamentous umbilical cord insertion and vasa previa
2. 前置胎盤の臨床的特徴、診断、および経過 clinical features diagnosis and course of placenta previa
3. 前置胎盤のマネージメント management of placenta previa
4. 胎盤の肉眼的評価 gross examination of the placenta
5. 妊婦における腟出血の病因および評価の概要 overview of the etiology and evaluation of vaginal bleeding in pregnant women

English Journal

Ultrasound in placental disorders.

D'Antonio F1, Bhide A2.Author information 1Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London SW17 0RE, UK.2Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London SW17 0RE, UK. Electronic address: abhide@sgul.ac.uk.AbstractThe definition of placenta previa based on ultrasound findings is more practical, and the traditional definition (implantation of the placenta in the lower uterine segment) needs to be revised. The term 'placenta previa' should only be used when the placental edge overlaps or is within 2 cm of the internal cervical orifice in late pregnancy. If the placental edge is located further than 2 cm but within 3.5 cm from the internal cervical orifice, the placenta should be termed 'low-lying'. Unless the placental edge at least reaches the internal orifice at mid-trimester, symptomatic placenta previa in the third trimester will not be encountered. Caesarean section is the recommended mode of delivery for placenta previa at term. Attempt at vaginal delivery is appropriate for low-lying placenta, but the possibility of post-partum haemorrhage should be kept in mind. The incidence of invasive placentation, such as placenta accrete, has progressively risen in the past 3 decades, possibly as a consequence of increasing caesarean section rates. Ultrasound has a sensitivity of 91% and a specificity of 97% for the identification of all forms of invasive placentation. Chorioangiomas are benign non-trophoblastic placental tumours with excessive vascular proliferation within the stroma of chronic villi. They are usually asymptomatic, although occasionally can be associated with adverse fetal outcomes. Chorioangiomas usually appear as well-circumscribed, rounded, hypo-echoic lesions next to the chorionic surface. Iatrogenic delivery or prenatal intervention are two options, if fetal compromise is present. Prenatal detection leads to a dramatic increase in survival compared with those cases unsuspected antenatally.
Best practice & research. Clinical obstetrics & gynaecology.Best Pract Res Clin Obstet Gynaecol.2014 Jan 14. pii: S1521-6934(14)00002-9. doi: 10.1016/j.bpobgyn.2014.01.001. [Epub ahead of print]
The definition of placenta previa based on ultrasound findings is more practical, and the traditional definition (implantation of the placenta in the lower uterine segment) needs to be revised. The term 'placenta previa' should only be used when the placental edge overlaps or is within 2 cm of the
PMID 24461676

Natural history of vasa previa across gestation using a screening protocol.

Rebarber A, Dolin C, Fox NS, Klauser CK, Saltzman DH, Roman AS.Author information Maternal-Fetal Medicine Associates, PLLC, 70 East 90th St, New York, NY 10128 USA. arebarber@mfmnyc.com.AbstractObjectives- The purpose of this study was to estimate the prevalence and persistence rate of vasa previa in at-risk pregnancies using a standardized screening protocol. Methods- We conducted a descriptive study of patients with a diagnosis of vasa previa from a single ultrasound unit between June 2005 and June 2012. Vasa previa was defined as a fetal vessel within 2 cm of the internal cervical os on transvaginal sonography. Screening for vasa previa using transvaginal sonography with color flow mapping was performed routinely in the following situations: resolved placenta previa, prior pregnancy with vasa previa, velamentous insertion of the cord in the lower uterine segment, placenta succenturiata in the lower uterine segment, and twin gestations. Results- A total of 27,573 patients were referred to our unit for fetal anatomic surveys over the study period. Thirty-one cases of vasa previa were identified, for an incidence of 1.1 per 1000 pregnancies. Twenty-nine cases had full records available for analysis. Five patients (17.2%) had migration and resolution of the vasa previa. When the diagnosis was made during the second trimester (<26 weeks), there was a 23.8% resolution rate (5 of 21); when the diagnosis was made in the third trimester, none resolved (0 of 8 cases). Of the 24 pregnancies (5 twin gestations and 19 singleton gestations) with persistent vasa previa, there was 100% perinatal survival and a median length of gestation of 35 weeks (range, 27 weeks 5 days-36 weeks 5 days). No known missed cases were identified over the study period. Conclusions- The use of standardized screening for vasa previa based on focused criteria was found to be effective in diagnosing vasa previa, with a 100% survival rate. Vasa previa diagnosed during the second trimester resolves in approximately 25% of cases.
Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine.J Ultrasound Med.2014 Jan;33(1):141-7. doi: 10.7863/ultra.33.1.141.
Objectives- The purpose of this study was to estimate the prevalence and persistence rate of vasa previa in at-risk pregnancies using a standardized screening protocol. Methods- We conducted a descriptive study of patients with a diagnosis of vasa previa from a single ultrasound unit between June 20
PMID 24371109

Japanese Journal

出生前診断した前置血管5例の解析

三浦裕美子,久保隆彦,本村健一郎,堀谷まどか,林聡,塚原優己,左合治彦,北川道弘
日本周産期・新生児医学会雑誌 = Journal of Japan Society of Perinatal and Neonatal Medicine 47(3), 589-594, 2011-08-30
NAID 10029551882