Velamentous cord insertion

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

Epidemiology

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.

Pathology

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.

Associations

• bilobed placenta
• increased incidence in twin pregnancy
• uterine anomalies ¹⁰
• presence of an intrauterine contraceptive device (IUCD) ¹⁰
• single umbilical artery ⁶
• placenta previa

Radiographic features

Antenatal ultrasound

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.

Complications

• 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.

See also

• Battledore placenta (marginal cord insertion)