Like most sites this site uses cookies : By continuing to use our site you are agreeing to our cookie policy.close & accept [x]
Resources Centre / Twins Tips Introduction / Twins Tips / Monochorionic Monoamniotic Twins - High Risk Pregnancy
Monochorionic Monoamniotic Twins - High Risk Pregnancy
A twin pregnancy can mean twice the excitement and twice the fun for a mum-to-be. After all. what can be better than welcoming two bundles of joy?

Unfortunately. twin pregnancies can also be quite challenging at times. causing twice the morning sickness and twice the fatigue. It can also be particularly stressful if your twins happen to be monoamniotic.

Monoamniotic twins are quite rare. but require special care and monitoring. Monoamniotic triplets can also develop. but this is extremely rare.Here is some essential information if you are expecting monoamniotic twins.
What are Monoamniotic Twins?
Mono-amniotic twins are identical twins that develop inside the same amniotic sac. Also known as Mo-Mo twins (Monoamniotic-Monochorionic). monoamniotic twins are always identical. These share a placenta within their mother"s uterus. but have two separate umbilical cords for nourishment. Mono-amniotic twins are rare. occurring in approximately 1 in 35.000 to 1 in 60.000 pregnancies. Unfortunately. monoamniotic twins are at great risk for health complications due to the close proximity of the two umbilical cords in the amniotic sac. This makes it particularly easy for the twins to become entangled in each other"s cords. or to compress one another"s cords. endangering their oxygen and food supply. The survival rate for mono-amniotic twins is approximately 50%.
Why Do Monoamniotic Twins Form?
No one is really sure why monoamniotic twins develop. Identical twins (also known as monozygotic twins) develop from a single fertilized egg that splits at some point after fertilization resulting in two or more identical zygotes.The timing of the division determines the separateness of the placentas and amniotic sacs. Typically this split occurs a few days after fertilization. just after the placenta forms but before the development of the amniotic sacs. These twins share a placenta but have individual amniotic sacs.

However. sometimes the fertilized embryo does not split until after the formation of the amniotic sac. When division occurs after eight days following fertilization. fetuses share a single placenta and a single amniotic sac (monoamniotic). About 5 percent of monozygotic twins are monoamniotic but this represents only 1% of all twins.
Recent research has shown a correlation between the number of yolk sacs present in pregnancy and the number of amniotic sacs twins will have. The yolk sac forms just after conception occurs and is thought to play a role in nourishing the developing embryo. With twins. there can be one yolk sac or two yolk sacs.

It has been found that twins with two yolk sacs are much more likely to have two separate amniotic sacs. On the other hand. twins with just one yolk sac seem to be more likely to have only one amniotic sac. Unfortunately. it is very difficult to detect the number of yolk sacs present during pregnancy. because the yolk sac disappears in the initial weeks of the first trimester.
Complications Associated with Monoamniotic Twins
Unfortunately. monoamniotic twins face a lot of potential health hazards throughout pregnancy. Many of these can be life threatening. so it is important to make sure that you receive specialised care if you are experiencing this type of twin pregnancy.

Nancy Bowers. B.S.N.. a registered nurse and author of The Multiple Pregnancy Sourcebook: Pregnancy and the First Days with Twins. Triplets. and More. says that while monoamniotic twins are quite rare. there are a lot of risks involved.
"Because the fetuses share an amniotic sac. they are at high risk for many problems." says Bowers. "The most common and dangerous complication is cord entanglement. Monoamniotic twins are also at increased risk for birth defects. The mortality rate for such pregnancies is usually quoted as about 50 percent. but because of better monitoring. there have been better outcomes in recent years."

Possible complications include:
  • Cord Entanglement: Cord entanglement is one of the main complications associated with monoamniotic twins. Because the twins have no amniotic membrane separating them. their umbilical cords can easily become entangled. This can hinder fetal movement and development. Additionally. if the twins become tied together in the uterus. one twin may become stuck in the birth canal during labour and delivery. which can be life threatening. Cord entanglement happens to some degree in almost all monoamniotic pregnancies.
  • Cord Compression: Cord compression is another life threatening condition common in monoamniotic twins. As the twins move around in the amniotic sac. it is possible that one will compress the other"s umbilical cord. This can prevent vital nutrients and blood from traveling to the other baby. resulting in fetal death.
  • Twin-to-Twin Transfusion Syndrome (TTTS): Twin-to-twin transfusion syndrome can occur in monoamniotic twins. This syndrome happens when one twin receives the majority of the nourishment in the womb. causing the other twin to become undernourished and sickly. Typically. TTTS is diagnosed by examining fluid levels in the two amniotic sacs. But because monoamniotic twins only have one amniotic sac. diagnosis of TTTS is much more difficult. Diagnosis rests on comparing the physical development of both of the twins.
  • Premature Birth: All monoamniotic twins are born prematurely. This is because full-term pregnancy is deemed unsafe by most medical professionals. The risk for cord entanglement and compression simply becomes too great and they may be delivered by caesearean after 34 weeks. However. many monoamniotic twins experience life-threatening complications as early as 26 weeks. and need to be delivered immediately. Preterm delivery is often associated with a number of life-threatening conditions.
Treatment for Monoamniotic Twins
Unfortunately. there is no treatment that can reverse this pregnancy condition. There are also few medical treatments available to improve the situation. An experimental drug. Sulindac. has been used to in some monoamniotic twins. This drug lowers the amount of fluid in the amniotic sac thereby reducing the amount of fetal movement. This is thought to lower the chances of cord entanglement or compression. However. this drug has not been studied in a large number of pregnancies and its potential side effects are unknown.
The best treatment for monoamniotic twins is to have regular and aggressive fetal monitoring. You should be sure to see a perinatologist (also called a maternal-fetal medicine specialist but basically this is a specialist in high risk pregnancies) regularly throughout your pregnancy. You should have twice-weekly monitoring of fetal heart rate and movement. particularly after the 26th week. After the 28th week. many women enter the hospital. so that they can be constantly monitored. Aggressive monitoring can help to lower the risk of fetal death considerably.

Tips for Parents who are expecting Monoamniotic Twins:
  • Don't stress too much if you have been diagnosed by your consultant on a regular resolution ultrasound machine. especially if the diagnosis comes before 12 weeks. Don't consider your diagnosis confirmed until you have been to see a high-risk specialist for a high-resolution ultrasound.
  • Map out an aggressive management plan with your specialist. Don't assume that the plan they give you is all that you can get. Don't be afraid to seek another opinion about the management of your pregnancy.
  • Most experts and parents recommend daily non-stress tests toward the end of the pregnancy.
  • Women with a monoamniotic multiple pregnancy should be cared for by a maternal-fetal specialist (perinatologist).
Support Organisations :
Monoamniotic Monochorionic Support Site
This group was formed by experienced and expectant parents reaching out to each other to help support each other through the difficult times and has members from all over the world.

Looking for more information on Twin Pregnancy & Multiple Births


< Back

Back to Resources Centre


Search Twins Tips

Back to Resources Centre
Twins ! Pregnancy. Birth and the First Year of Life
.Twins & Multiples Birth Book Essential Guide

Copyright 2008 Twins International Ltd.