Monochorionic / Identical Twins

Monochorionic/Identical Twins 

Patient Information

Obstetrics & Gynaecology Department

• Author ID: FK
• Leaflet ref: Obs 032
• Version: 8
• Leaflet title: Monochorionic/Identical Twins
• Last review: December 2022
• Expiry Date: December 2024

Introduction

Your ultrasound scan has shown that you are expecting twins that are monochorionic (shared placenta) or identical twins.  This leaflet is designed to explain what this means to you.

Twins can be: 

• Dichorionic Diamniotic (DCDA) – This means each baby has its own placenta and its own sac. This is the most common type of twin pregnancy. 
• Monochorionic Diamniotic (MCDA) – This means the babies share a placenta but they are each in their own sacs. 
• Monochorionic Monoamniotic (MCMA) – This means that both babies share a placenta and are within the same sac. This is a much rarer type of twin pregnancy.

What are monochorionic twins?

These are twins that come from the same egg, which splits into two babies as the cells divide.  This means that they share the same placenta (afterbirth) and that they are identical.

What does this mean to me?

In the majority of women, these pregnancies progress normally, but there is a higher risk of problems than with a single pregnancy, or with a twin pregnancy where each baby has their own placenta (dichorionic pregnancies).

You need to be aware of the following factors:

• You might experience more sickness and tiredness in a twin pregnancy.
• You will need regular check-ups with your obstetrician, GP or midwife, as there is an increased risk of developing pre-eclampsia (a pregnancy condition with high blood pressure and protein in the urine), so careful monitoring of your blood pressure and urine will help to identify preeclampsia earlier and manage it appropriately..
• You will be offered regular scans during the pregnancy, starting at 16 weeks and then every 2 weeks, to check on the size of the babies and to measure the fluid around them.
• You need to be observed for signs of excessive fluid developing around the babies (a condition called polyhydraminos).  This may mean a problem may be developing with your babies that requires further assessment.  If you experience a sudden growth in your abdominal measurement, or an uncomfortable, tense and rigid abdomen, then you need to attend your local hospital as soon as possible, as this can bring on early labour.

Where will my twins be born?

• It is recommended that you plan to have your babies at a unit that has appropriate monitoring equipment and medical staff on hand, should there be a need for a Caesarean Section. This includes Wigan Maternity Unit for twins over 28 complete weeks gestation, 800gm (1pound and 12.2 ounces) estimated weight and in absence of complex birth defects (eg. complex heart problems, genetic or nervous system problems).
• Occasionally, during pregnancy, you may need to be transferred to a tertiary baby care unit, i.e. one that has special facilities for more advanced care and treatment for babies, if it is deemed safe to do so. This transfer will be arranged, if delivery is likely to occur at <28 weeks of pregnancy, estimated foetal weight <800gm (1pound and 12.2 ounces), or any foetal complications for which a high level Neonatal Intensive Care input may be required for the babies at birth.
• Heart trace monitoring of the babies is advised to help midwives and medical staff manage your labour and delivery safely.
• If the first baby is head down and there have been no problems, then we would usually aim for a vaginal delivery.  If the first baby is not head down, caesarean section is usually recommended, but you will get the opportunity to discuss this further with the medical staff.
• We would aim to deliver your babies at about 36 to 37 weeks, as occasionally identical twins can develop problems after this time.  However, if complications occur or you go into early labour this may mean they need to be delivered sooner.
• Planned delivery at 36 to 37 weeks does not appear to cause an increased risk of serious problems for your  babies

Will there be any problems associated with having monochorionic twins?

• The babies share the same placenta and there are connections between the babies’ blood circulation systems.  In about15% of cases this can cause problems, if blood flows from one twin to the other.  This means that one twin (recipient twin) may have more blood flow, causing it to grow bigger than the other twin (donor twin), who has less blood flow, and can be smaller.  This also causes the larger twin to have a large bladder and produce more urine, which in turn causes an imbalance in the amount of amniotic fluid(which is baby’s urine), surrounding the twins.  If this continues, then the smaller twin produces less urine and has less fluid within its sac, (large cavity of fluid surrounding the embryo) causing it to become closely wrapped in it.  This is called twin-to-twin transfusion syndrome (TTTS).
• This process can become severe and could lead to problems for both twins, depending on how rapidly it develops and at what stage of pregnancy it happens. For this reason, we would like to see you and scan you regularly to check on the babies’ growth and wellbeing, and also to measure the fluid around each baby.

Is there any treatment for twin-to-twin transfusion syndrome?

• If you develop this syndrome, then you will be referred to the Fetal Medicine Unit at St Mary’s Hospital or Liverpool Women’s Hospital, where they see women with this condition from all over the North West.
• There are certain treatments for this condition (eg Laser) and if they are required, the Specialist Consultant will discuss them in greater detail with you.  It usually involves the use of a laser to block the placental blood vessels that connect the circulation of the twins.  This is undertaken under a detailed ultrasound examination.  The treatment and outcomes are individualised and you will get an opportunity to discuss it with them if needed.

If you have any questions about this leaflet, please do not hesitate to contact us via the Antenatal Clinic number on your hand held notes.