Marginal cord insertion (MCI), sometimes referred to as battledore placenta, is a variation where the umbilical cord connects near the edge rather than the center of the placental disc. The umbilical cord transports oxygenated blood and nutrients from the placenta to the developing fetus. MCI is one of the more common anatomical deviations, occurring in approximately 5% to 9% of singleton pregnancies. While this variation is generally considered a benign finding, its presence warrants closer attention. The diagnosis of MCI allows healthcare providers to implement appropriate surveillance.
Understanding the Anatomy of Marginal Cord Insertion
A normal or central cord insertion means the umbilical cord inserts directly into the middle of the placental disc, which is typically the thickest area. When the insertion point is slightly off-center but still well within the main placental body, it is termed an eccentric cord insertion.
Marginal cord insertion is defined when the umbilical cord enters the placenta within two centimeters of the placental edge. This peripheral location means the cord is attached to a thinner area of placental tissue. The vessels may have less protective cushioning from Wharton’s jelly, the gelatinous substance surrounding the vessels.
This anatomical arrangement can potentially affect the efficiency of nutrient and oxygen transfer compared to a central attachment. The proximity to the edge may lead to a reduced number of large, branching blood vessels near the insertion site. This structural difference necessitates careful observation during the pregnancy, although the majority of pregnancies with MCI progress without complications.
How Marginal Cord Insertion is Diagnosed and Distinguished
The primary method for identifying marginal cord insertion is through routine prenatal ultrasound imaging. This finding is most often detected during the second-trimester anatomy scan, typically occurring between 18 and 22 weeks of gestation. Sonographers use grayscale and color Doppler imaging to visualize the exact point where the umbilical cord connects to the placental tissue.
Diagnosis is established by measuring the distance from the cord insertion site to the nearest edge of the placenta. An insertion measurement of two centimeters or less is the accepted threshold for classifying the attachment as marginal. Color Doppler is particularly helpful, as it highlights the blood flow, allowing clinicians to trace the vessels directly into the placental tissue.
It is important to distinguish marginal cord insertion from velamentous cord insertion (VCI), a more serious condition. With marginal insertion, the vessels are protected because they insert into the edge of the placental tissue. In contrast, VCI occurs when the umbilical vessels separate and run unprotected within the amniotic membranes before reaching the placenta.
The vessels in a VCI are exposed and unsupported by Wharton’s jelly or placental tissue, making them highly vulnerable to compression or rupture. Since MCI vessels remain attached to the placental mass, they retain some protection. This distinction is paramount for management, as VCI requires a significantly higher level of intensive surveillance.
Specialized Monitoring and Delivery Planning
Once a diagnosis of marginal cord insertion is confirmed, the management plan shifts to increased surveillance focused on mitigating potential secondary effects. The primary concern is monitoring for adequate fetal growth, as the suboptimal insertion may, in a small number of cases, reduce the efficiency of nutrient delivery.
The most common specialized monitoring tool is the serial growth ultrasound, used to screen for Fetal Growth Restriction (FGR). These scans are often scheduled more frequently, typically every four to six weeks in the third trimester, to track the baby’s size and weight trajectory. Doppler flow studies may also be incorporated to assess the blood flow dynamics within the umbilical cord vessels, providing an early indication of placental function.
If fetal growth remains on track, the pregnancy can proceed normally to term. Most pregnancies with MCI result in successful outcomes, and a vaginal delivery is typically appropriate. During labor, healthcare providers often recommend continuous fetal heart rate monitoring. This practice allows for the immediate detection of potential cord compression or changes in the baby’s well-being.