The placenta and umbilical cord are the lifelines between mother and baby during pregnancy. The umbilical cord attaches to the placenta and enables the delivery of maternal oxygen and nutrients to the baby. The proper functioning of this delivery system is critical to fetal development.
The umbilical cord insertion (or attachment) to the placenta is a key part of this delivery system. There are 4 different types of umbilical cord insertions to the placenta. Only two of these four types of umbilical cord insertion are considered to be abnormal: (1) marginal cord insertion and, (2) velamentous cord insertion. This page will focus on marginal cord insertion or MCI, which is the less dangerous of the 2 abnormal cord insertions.
Normally the umbilical cord is supposed to insert and attach to the center of the placenta (central cord insertion). A marginal umbilical cord insertion occurs when the cord attaches on the side of the placenta instead of in the middle at the central placental mass. Marginal cord insertion is considered abnormal and it occurs in roughly 9 out of every 100 pregnancies.
Think of it this way: In a normal pregnancy, the umbilical cord is attached to the center of the placenta, which allows for an equal distribution of nutrients and oxygen to the developing fetus. However, in cases of marginal cord insertion, the cord is attached to the edge of the placenta, which can cause complications in some pregnancies.
Marginal cord insertion is problematic because the sides of the placenta are much weaker and have less tissue compared to the central area of the placenta where the cord is supposed to insert. The weaker sidewalls of the placenta are not able to properly support the cord attachment the same way that the central placental mass can.
The exact causes of marginal cord insertion are not understood. But it is believed to be a result of abnormal development of the placenta during early pregnancy.
No causative factors have been linked to marginal umbilical cord insertion and there is no genetic, racial, or geographical predisposition associated with this condition. The one well-known risk factor for marginal cord insertion is a multiple pregnancy. Marginal cord insertions (and all abnormal cord insertions) are three to four times more likely with twin and multiple pregnancies. New research has also found that the marginal insertion of the umbilical cord is more likely when fertility treatments are used to help conceive.
Marginal cord insertion does not result in any noticeable physical symptoms early in the pregnancy. Abnormal insertion of the umbilical cord is fairly easy to diagnose with a prenatal ultrasound and physical examination. The problem is that ultrasound scanning cannot determine the type of placenta and umbilical cord abnormality.
Still, a diagnosis of marginal cord insertion can often be made during routine ultrasound examinations that are typically performed during pregnancy. Ultrasound is a non-invasive imaging technique that uses high-frequency sound waves to create images of the developing fetus and placenta. During the ultrasound, the doctor will examine the placenta and umbilical cord and look for any signs of marginal cord insertion.
If marginal cord insertion is diagnosed, there is cause for concern but there is no panic. The doctor will typically monitor the pregnancy more closely to ensure that the developing fetus is receiving enough nutrients and oxygen. This may involve more frequent ultrasounds to monitor fetal growth and development, as well as fetal heart rate monitoring to assess the baby’s wellbeing. The key is the doctor maintaining the concern throughout the pregnancy.
There are several potential risks associated with marginal cord insertion. One of the most common risks is a decreased supply of nutrients and oxygen to the developing fetus. This can result in growth restriction or even stillbirth in severe cases. Additionally, marginal cord insertion can increase the risk of other complications during pregnancy, such as preterm birth and cesarean delivery.
Any abnormal cord insertion, including marginal cord insertion, can potentially result in placental development problems which can impact fetal development and growth. Marginal cord insertion can restrict or reduce the blood flow and circulation to the fetus during pregnancy. Reduced fetal blood flow can cause intrauterine growth restriction (IUGR) and other developmental abnormalities in the fetus.
Marginal cord insertion (and the secondary conditions it can lead to such as IUGR) can potentially result in premature birth. Some studies have found that that marginal cord insertion might increase the chances of spontaneous abortion in the 1st or 2nd trimester, but the risk increase is comparatively small. Another potential risk with marginal cord insertion is excessive bleeding during vaginal childbirth.
Marginal cord insertion can also increase the chances of developing another placental complication known as placenta previa. Placenta previa occurs when the placenta is abnormally located at the bottom of the womb and is partially or completely blocking the entrance to the birth canal.
Vasa previa is a rare but potentially dangerous condition in which fetal blood vessels are present in the amniotic sac instead of being contained within the umbilical cord. Vasa previa is a complication that is mostly related to velamentous cord insertion, but marginal cord insertion can also make vasa previa more likely.
Vasa previa can be dangerous if not diagnosed before vaginal delivery is attempted. During normal childbirth, the amniotic sac ruptures to allow the baby to travel through the birth canal. When vasa previa is present this normal rupturing of the amniotic sac can be very dangerous because the fetal blood vessels in the amniotic sac will also rupture. The result is significant blood loss for the baby. When vaginal delivery is attempted in a vasa previa pregnancy there is a high risk that the baby will bleed to death before they are born.
While vasa previa and marginal cord insertion are not the same condition, they can be related in some cases. Both conditions involve abnormalities in the umbilical cord and its attachment to the placenta, which can impact fetal health and the delivery process.
In some cases, vasa previa can be caused by marginal cord insertion. When the cord inserts at the edge of the placenta, it can lead to abnormal branching of the blood vessels, which can cross the cervix and result in vasa previa. This is because the blood vessels are not protected by the jelly-like substance called Wharton’s jelly that is found in the central portion of the umbilical cord. Without this protection, the velamentous vessels can easily rupture during labor, leading to significant bleeding and other complications.
It is important to note that not all cases of marginal cord insertion will result in vasa previa, and not all cases of vasa previa are caused by marginal cord insertion. Other factors, such as a low-lying placenta or multiple pregnancies, can also increase the risk of vasa previa.
Both vasa previa and marginal cord insertion can be diagnosed through prenatal screening, which may include ultrasound imaging or other diagnostic tests. Early diagnosis and management of these conditions are critical for ensuring the health and safety of the fetus during delivery.
In some cases, vasa previa can be managed through careful monitoring and planned delivery via cesarean section, using a slightly different way of performing the procedure. Marginal cord insertion, on the other hand, typically does not require specific management or intervention unless it is associated with other complications, such as fetal growth restriction.
There is no effective treatment to correct marginal umbilical cord insertion. Once the umbilical cord attaches abnormally there is nothing doctors can do to correct the attachment. Marginal cord insertion can be very effectively managed to a good outcome, however, as long as the condition is timely diagnosed and carefully monitored. A C-section delivery may be advised for women with MCI.
Ecker, J. Velamentous umbilical cord insertion and vasa previa. UpToDate (2022). The article discusses the risk factors, diagnosis, and management of both conditions. For velamentous cord insertion, careful monitoring and management during pregnancy and delivery can help reduce the risk of complications. In cases of vasa previa, early diagnosis and planned delivery by cesarean section can be lifesaving for the fetus.
Cui, X., et. al (2021). Marginal cord insertion and perinatal outcomes: A systematic review and meta-analysis. PloS one, 16(1), e0245646 (2021).
Allaf, M.B., et al. “Second trimester marginal cord insertion is associated with adverse perinatal outcomes.” The Journal of Maternal-Fetal & Neonatal Medicine 32.18 (2019): 2979-2984. (This study examined the feasibility of evaluating placental cord insertions to determine marginal cord insertions’ associations with low birth weight and preterm delivery. The researchers concluded that it was feasible to evaluate placental cord insertions. They also concluded that marginal cord insertions increased the risk of preterm delivery, low birth weight, and other adverse outcomes.)
Aragie, H., & Oumer, M. “Marginal cord insertion among singleton births at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia.” BMC Pregnancy and Childbirth 21.1 (2021): 1-10. (This study looked at the association between marginal cord insertions and adverse outcomes in singleton births. The researchers concluded that marginal cord insertions increased the risk for preterm deliveries, low birth weights, and emergency C-sections. They recommended that healthcare providers screen for marginal cord insertions in pregnancies involving advanced age, nulliparity, hypertension, a C-section history, and prior IUD use.)
Lutz, A.B., et al. “Measurement of Marginal Placental Cord Insertion by Prenatal Ultrasound Was Found Not to Be Predictive of Adverse Perinatal Outcomes.” Journal of Ultrasound in Medicine (2020). (This study examined marginal cord insertions’ association with perinatal outcomes. It also examined a prenatal ultrasound’s ability to predict adverse perinatal outcomes. Their data suggested that marginal cord insertion pregnancies may not increase the adverse perinatal outcome risk.)
Nkwabong, E., Njikam, F., & Kalla, G. “Outcome of pregnancies with marginal umbilical cord insertion.” The Journal of Maternal-Fetal & Neonatal Medicine 34.7 (2021): 1133-1137. (This study looked at labor outcomes associated with marginal cord insertions. The researchers found significant associations with pre-eclampsia, nuchal cord entanglements, placenta abruptions, low birth weights, and NICU transfers. They concluded that deliveries involving marginal cord insertions should occur in NICU hospitals.)
Tian, Y., Luo, H., & He, M. “Effects of marginal umbilical cord insertion on the prognosis of fetus.” Clinical and Experimental Obstetrics & Gynecology 47.2 (2020): 234-237. (This study looked at marginal cord insertion’s effect on fetal prognosis. Researchers found that that low birth weights were more prevalent in the marginal cord insertions than in normal umbilical cord insertions. They also found that lower marginal insertions had lower placental and fetal weights compared to upper marginal insertions. The researchers concluded that healthcare providers should frequently monitor lower marginal cord insertions for abnormal fetal growth.)