Velamentous cord insertion
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Velamentous cord insertion is a type of abnormal umbilical cord insertion into the placenta.
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The estimated incidence is ~1% in singleton and 9-15% in twin pregnancies, respectively 11. It is also more common in placenta previa than in normally located placentas. The prevalence may be slightly higher in stillbirths, particularly from multifetal pregnancies.
In a velamentous cord insertion, the umbilical cord inserts into the fetal (chorio-amniotic) membranes outside the placental margin and then travels within the membranes to the placenta (between the amnion and the chorion). It is thought to result from remodeling of the placenta as a response to factors that affect the distribution of uterine blood flow (a process known as trophotropism 5). A marginal cord insertion may evolve into a velamentous cord insertion as the pregnancy progresses 6. Some also support an abnormal primary implantation due to the obliquity of the embryo during implantation as a cause.
- bilobed placenta
- increased incidence in twin pregnancy
- uterine anomalies 10
- presence of an intrauterine contraceptive device (IUCD) 10
- single umbilical artery 6
- placenta previa
Ultrasound allows direct visualization of the cord implantation to a site outside the placenta.
A velamentous cord insertion may be detected as early as the first-trimester scan 4. Antenatal ultrasound is considered to have a variable sensitivity (69-100%) but high specificity (99-100%) for revealing abnormal placental cord insertion sites, including velamentous insertions 5,8.
Color Doppler greatly aids in identification.
- type I vasa previa
- increased risk of intrauterine growth restriction (IUGR)
- increased risk of growth discordance if in a twin pregnancy
- increased risk of twin to twin transfusion syndrome
Treatment and prognosis
Treatment somewhat depends on the location of velamentous vessels and if in the lower segment, a cesarean section to avoid the risks of a vasa previa is often considered.
- Battledore placenta (marginal cord insertion)
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- 8. Nomiyama M, Toyota Y, Kawano H. Antenatal diagnosis of velamentous umbilical cord insertion and vasa previa with color Doppler imaging. Ultrasound Obstet Gynecol. 1998;12 (6): 426-9. doi:10.1046/j.1469-0705.1998.12060426.x - Pubmed citation
- 9. Benirschke K, Kaufmann P. Pathology of the human placenta. Springer Verlag. (2000) ISBN:0387988947. Read it at Google Books - Find it at Amazon
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- 11. Fadl S, Moshiri M, Fligner CL, Katz DS, Dighe M. Placental Imaging: Normal Appearance with Review of Pathologic Findings. Radiographics : a review publication of the Radiological Society of North America, Inc. 37 (3): 979-998. doi:10.1148/rg.2017160155 - Pubmed