Velamentous cord insertion

Last revised by Dr Jeremy Jones on 20 Sep 2021

Velamentous cord insertion is a type of abnormal umbilical cord insertion into the placenta.

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.

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.

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.

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Cases and figures

  • Figure 1: diagram
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  • Figure 2: bilobate placenta with velamentous cord insertion
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  • Case 1
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  • Case 2
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