What is an eccentric (marginal) umbilical cord insertion and how should it be managed in pregnancy?

Eccentric (Marginal) Umbilical Cord Insertion: Definition and Management

Eccentric umbilical cord insertion refers to cord insertion within 1 cm of the placental edge (marginal insertion), which is distinct from normal central insertion and should be documented during the second-trimester anatomy scan at 18-22 weeks using transabdominal ultrasound with color Doppler. 1

Definition and Classification

Marginal (eccentric) cord insertion occurs when the umbilical cord inserts at or near the placental edge, specifically within 1 cm of the margin. 2 This differs from:

• Normal insertion: >1 cm from placental edge 2
• Velamentous insertion: Cord inserts into membranes rather than placenta, with vessels traversing unprotected 1

The distinction matters clinically because velamentous insertion carries higher risk than marginal insertion, though both are considered abnormal. 1

Diagnostic Approach

Color Doppler ultrasound at the routine 18-22 week anatomy scan has 67% sensitivity and 100% specificity for detecting abnormal cord insertions. 3, 4

Key imaging steps include:

• Transabdominal ultrasound with color Doppler is the primary modality for identifying the placental cord insertion site 1, 4
• Transvaginal ultrasound with color Doppler should be added when abnormal insertion is identified to exclude vasa previa, as it has superior detection capability 3, 4
• The insertion site can be visualized in 99% of cases, with posterior placentas in the third trimester being most challenging 5

Clinical Significance and Associated Risks

Marginal cord insertion increases risk for several adverse outcomes, though the magnitude varies:

In singleton pregnancies:

• Fetal growth restriction and small for gestational age 1, 3
• Lower gestational age at birth 1
• Prematurity and low Apgar scores 5

In twin pregnancies (particularly monochorionic):

• Marginal or velamentous insertion occurs in up to 22% of monochorionic twins 1
• When abnormal insertion affects one or both twins, risk of twin-twin transfusion syndrome increases from 7% to 27% 1, 4
• Increased risk of selective fetal growth restriction and intrauterine fetal demise 1
• Higher frequency of concurrent vasa previa 1, 6

Surveillance Protocol

Once marginal insertion is identified, serial surveillance focusing on fetal growth, amniotic fluid, and umbilical artery Doppler should continue throughout pregnancy. 4

For singleton pregnancies:

• Serial growth assessments every 3-4 weeks 4
• Umbilical artery Doppler when growth restriction is suspected 4

For monochorionic twin pregnancies:

• More intensive surveillance with fetal biometry every 2-3 weeks starting at 16 weeks 4
• Estimated fetal weight discrepancy calculated and documented at each scan 1

Management and Delivery Planning

Vaginal delivery is generally preferred for singleton pregnancies with isolated marginal cord insertion without vasa previa, as cesarean delivery is reserved for standard obstetric indications. 3

Cesarean delivery should be strongly considered when:

• Marginal insertion is combined with fetal growth restriction AND abnormal umbilical artery Doppler findings 3, 4
• Twin gestations with marginal/velamentous insertion have additional risk factors or complications 3
• Vasa previa is identified on transvaginal ultrasound 3, 6

Critical Pitfall to Avoid

Never perform digital pelvic examination without first excluding vasa previa when abnormal cord insertion is identified, as this can trigger catastrophic vessel rupture. 6

Special Consideration: Umbilical Cord Hypocoiling

Umbilical cord hypocoiling (coiling index <0.1) is highly associated with abnormal cord insertion, occurring in 66.7% of hypocoiled cords versus only 1.3% of normally coiled cords. 7 When hypocoiling is identified sonographically, careful evaluation of the insertion site is warranted.