The umbilical cord connects the developing fetus to the placenta, which exchanges oxygen and nutrients necessary for growth. Marginal cord insertion (MCI) is a common variation where the umbilical cord attaches at an unusual location on the placenta. This anatomical difference is often identified during routine prenatal imaging.
Defining Marginal Cord Insertion
Marginal cord insertion, sometimes called a “battledore placenta,” describes a condition where the umbilical cord connects to the edge of the placenta rather than the center. Typically, the cord inserts near the middle, providing the most secure and direct access to the placental blood supply.
For a diagnosis of marginal cord insertion, the umbilical cord must enter the placenta less than two centimeters from the placental margin. If the cord inserts more than two centimeters from the edge but is still not central, it is usually categorized as an eccentric insertion.
This variation is not rare, occurring in approximately 6.15% to 7.5% of single-fetus pregnancies. The incidence is significantly higher in pregnancies involving multiples, such as twins. Marginal cord insertion is typically diagnosed during a routine second-trimester ultrasound.
Potential Fetal and Maternal Implications
The primary concern with a marginal insertion stems from the structural difference between the center and the edge of the placenta. The peripheral area where the cord attaches has a lower density of blood vessels compared to the central portion. This off-center attachment can lead to less efficient delivery of nutrients and oxygen to the fetus.
Research indicates that pregnancies with marginal cord insertion have a higher likelihood of resulting in a fetus that is small for gestational age or experiences Fetal Growth Restriction (FGR) compared to those with central insertions. The proximity to the edge means the blood vessels are less protected by the surrounding tissue, making them more vulnerable to compression or kinking.
The degree of marginality influences the magnitude of the risk; insertions closer to the absolute edge are associated with a greater chance of adverse outcomes. This suboptimal nutrient exchange can also increase the risk of preterm birth (delivery before 37 weeks). The impact on fetal development can lead to a lower mean birth weight at delivery.
Maternal implications include a slightly increased risk of developing preeclampsia, characterized by high blood pressure during pregnancy. There is also an elevated risk of placental abruption, the premature separation of the placenta from the uterine wall. The fragile nature of the cord’s insertion point may also contribute to excessive bleeding or hemorrhage if the placenta is manually removed after delivery.
Monitoring and Delivery Planning
Once marginal cord insertion is identified, clinical management shifts toward increased surveillance to mitigate potential risks. Since there is no intervention to physically correct the cord’s position, the focus is on closely monitoring the fetus for signs of growth or blood flow issues. This typically involves more frequent third-trimester prenatal visits and specialized testing.
Serial ultrasound examinations are often scheduled to track the fetus’s growth trajectory and estimate its weight. These scans help confirm that the fetus is receiving adequate nutrition and is developing appropriately. Doppler studies measure the blood flow through the umbilical cord and other fetal vessels, providing detailed information about placental function.
In addition to growth checks, non-stress tests and biophysical profiles may be used to assess fetal well-being, monitoring the fetal heart rate and movement patterns. These tests help the medical team identify any signs of distress that might warrant earlier intervention. The goal of intensified monitoring is to allow the pregnancy to continue as long as it is safe for the fetus.
For delivery, marginal cord insertion does not automatically necessitate a Cesarean section, and most women can still have a normal vaginal delivery. Continuous fetal heart rate monitoring is usually recommended throughout labor to quickly detect any compromise in blood flow as contractions progress. In rare instances, a marginal insertion can progress to velamentous cord insertion, where the blood vessels travel unprotected across the membranes, which may require a planned Cesarean delivery due to the risk of vessel rupture.