From the moment of conception, when the egg meet the sperm, a very complex process of cell division and specification happens. Each new cell will be in charge of a very specific part of the baby, the umbilical cord or the placenta and fetal membranes.
This will happen in all pregnancies: singleton and twin pregnancies.
This specification happens at a very early stage. The placenta and umbilical cord at this moment are just a handful of identical cells that start playing their part very precisely as the cord attaches to the placenta. It’s only as the pregnancy advances and the placenta and umbilical cord grow that it’s possible to notice the abnormal placental cord insertion.
What is an abnormal umbilical cord?
The word ‘abnormal’ tends to be quite scary but this is because of the misconception we tend to have about what ‘normal’ means. Abnormal simply means ‘not normal’ and normal is just a statistical term that indicates where the majority is.
Taking this into account, the term ‘abnormal cord insertions’ refers to those umbilical cords whose placental insertion site differs from the majority of umbilical cord sites.
What is cord insertion in pregnancy?
During the first few weeks of pregnancy, as the cells specialize remarkably. The majority of these cells will specialize in the baby. Some cells will develop the placenta, some the cord, and some will specialize in the placental cord insert site.
The way the umbilical cord inserts into the placenta is one of the most common abnormalities during pregnancy. This doesn’t necessarily mean there will be pregnancy complications. Often, it just means a rare insertion of the umbilical cord, which carries the pregnancy to full term without any adverse pregnancy outcomes.
Cord insertion types
The umbilical cord is the channel between the placenta and the baby. The cord connection in the placenta can happen at different sites.
#1: Central cord insertion
A central cord connection is the most common type of umbilical cord insertion; it is the ‘normal’ cord connection. The cord meets the placenta at its center. Research shows that this happens in 88-91% of pregnancies.
#2: Eccentric cord insertion
An eccentric cord insertion is a non-central cord connection.
#3: Marginal cord insertion
A placental cord insertion at the very edge of the placenta, where it meets the membrane.
Is marginal cord insertion dangerous?
A marginal cord insertion isn’t dangerous per se. Where there is a marginal cord connection, most pregnancies carry on to full term without any complications. Many instances of this are actually missed during prenatal ultrasonography and are only diagnosed after birth when live placental cord insertion visualization occurs.
Does marginal cord insertion require c-section?
There are very few physiological (naturally caused) conditions that require a cesarean section. The vast majority of cesarean sections are performed because of increased medicalization of birth.
You can read more about this in New Research Uncovers Two Main Causes Of C-Sections.
A marginal cord insertion is not an excuse to perform a c-section. A c-section has many other risk factors. The risks are far greater than a vaginal birth with a placenta that has been working perfectly throughout the whole pregnancy.
Read more about the risks of cesarean sections in US Women Have Too Many C-Sections, With Too Much Risk.
#4: Velamentous cord insertion
A velamentous cord insertion occurs when the umbilical cord inserts into the membranes. These membranous umbilical vessels then travel to reach the placenta.
Can you have a healthy baby with velamentous cord insertion?
Absolutely. The vast majority of pregnancies with a velamentous umbilical cord carry on to full term without any complications.
Research shows that these cords are usually quite rare in singleton pregnancies. A velamentous cord insertion affects around 1% of singleton pregnancies. However, the rate of velamentous cord insertion rises to 15% in twin pregnancies.
Some velamentous cords are found via a prenatal ultrasound diagnosis. Some are just discovered postnatally when the placenta is examined.
In most cases, in singleton pregnancies with a velamentous umbilical cord abnormality, fetal development is rarely affected. The flow through the umbilical cord remains normal and there isn’t a fetal growth restriction.
Cord insertion and vasa previa
Many discoveries and interventions in the obstetrics and gynecology field can save lives. However, some of these interventions can put lives at risk, too. An isolated velamentous cord insertion is a good example of how overmedicalization of birth can be very dangerous.
Any pregnancy with a velamentous cord insertion can carry on to full term and it usually does, without any complications.
The biggest threat a velamentous cord insertion carries is a rupture of one of the umbilical cord vessels that run through the membranes.
Vasa previa is when the part of the membranes where these umbilical cord vessels are, are present just behind the cervix.
When the bag of waters ruptures spontaneously, the chances of breaking one of these fetal blood vessels that run through the membranes are very slim. This is because the membranes break through at the weakest point. If the tear in the bag approaches a blood vessel, it will very likely run alongside the vessel and not through it.
The biggest threat to a velamentous cord insertion is an artificial rupture of the membranes. When there’s an undiagnosed velamentous cord insertion and a fetal blood vessel is punctured, adverse perinatal outcomes might follow. A ruptured vasa previa is one of the most serious complications in childbirth; it carries the highest risk of adverse outcomes for both mother and baby.
There should always be a genuinely good reason for any medical intervention. And no intervention should ever happen without the woman’s consent.
You can get more information in 8 Reasons To Say No To Labour Induction.
When a velamentous insertion is diagnosed prenatally, the most important measure the obstetric team will take is to make sure an artificial rupture of membranes isn’t performed. When the ultrasound diagnoses velamentous cord insertion, there’s not much that can be done, apart from monitoring it closely and avoiding unnecessary intervention.
What causes abnormal cord insertion?
Here are some of the most common risk factors for abnormal cord insertions and placental implantation abnormalities:
- Any condition that affects the mother’s health, such as diabetes or drug abuse, can cause umbilical cord abnormalities
- The use of artificial hormones, such as the use of an intrauterine device (IUD) before pregnancy or the use of artificial reproductive technology (ART)
- Marginal cords are also more common in first pregnancies and if the mother is over 40 years of age
- When the umbilical cord has just one artery instead of two, velamentous and marginal cord insertions are more likely to happen.
Read more about this in Single Artery Umbilical Cord – What Does It Mean?
- Marginal and velamentous cords are much more common in multiple pregnancies. The rate is 15%, compared with the 1% likelihood when there’s just one baby.
Risks of eccentric cord insertion
Although the vast majority of pregnancies carry on to full term without any complications, an abnormal umbilical cord can place the baby, and sometimes the mother, at a higher risk of:
- Abnormal fetal growth. If the blood flow is compromised due to an abnormal cord insertion, the baby might suffer from intrauterine growth restriction. Your health care provider will make sure you and your baby are well taken care of and your baby’s intrauterine growth will be closely monitored. Make sure you understand well what’s happening and how your pregnancy develops
- Premature birth. Your baby might be born prematurely if there has been some kind of growth restriction
- Placental complications. The way the placenta is inserted in the uterine wall might also be compromised, so the risk of placental complications is higher. These complications include placenta previa, placental abruption, and postpartum hemorrhage, due to difficult detachment of the placenta after birth.
Can cord insertion change?
Sometimes a marginal cord corrects itself as the pregnancy develops and the placenta grows. When the placenta becomes bigger, the cord insertion might go a little further into the placental tissue.
This might happen in a marginal cord. In a velamentous cord, however, it is more difficult for this to happen, as the cord insertion is quite far away from the placental tissue.
What is the normal length of the umbilical cord?
The umbilical cord is usually around 55cm long.
However, it tends to grow longer, as required. When the cord gets tangled around the baby’s body or neck (nuchal cord), it tends to grow larger, allowing the baby to keep moving while it serves its purpose. When a baby has several loops around the neck, it’s not because the cord was very long and therefore became tangled. In fact, because the cord was wrapped around the baby, it has grown longer.