Twin-twin (feto-fetal) transfusion syndrome:

This condition affects approximately 1 in 5 (20%) of all twins that share the same placental mass (monochorionic).  This is a highly pathological condition, which if untreated will lead to fetal or newborn death in excess of 95% of cases.

The underlying abnormality is that the placenta contains vascular connections that connect the twins, in effect, making them connected together by a continuous blood supply.

One of the very early ultrasound signs of twin-twin transfusion syndrome is that one set has a relatively large nuchal translucency (collection of fluid at the back of the baby’s neck), whilst the other appears normal.  This is often observable at between 10 – 14 weeks of gestation and is predictor of Twin-Twin Transfusion syndrome in approximately 70% of cases.

The vascular (blood supply) connection between twins within the placenta leads to a haemodynamic (blood flow) imbalance between the twins, with one, the recipient, having a relative high perfusion of blood and the other, the donor, being under perfused with blood.

Fetoscopy for Placental Laser Ablation

In the majority of cases the pregnancies are treated by fetoscopic laser ablation.

However, this is very specialized treatment and the pregnancy needs careful evaluation.

All treatment is individualized

Diagnosing and Classifying Twin to Twin Transfusion Syndrome

It is possible to make the diagnosis using ultrasound.  The severity of the condition is denoted by a staging classification:

Stage 1. There is a difference in the amounts of amniotic fluid surrounding the twins.  The recipient often is complicated by polyhydramnios (excess amniotic fluid with a maximum pool depth of around 8cms) and the donor is complicated by oligohydramnios (reduced amniotic fluid with a maximum pool depth of around 2cms).

Stage 2. In addition to the discrepancy of amniotic fluid volumes, there is a difference in size between the two babies (the recipient is often larger than the donor).

Stage 3. There are haemodynamic differences between the twins.  The recipient has evidence of abnormal blood flow and right-sided heart strain. The donor often demonstrates absent or reversed blood flow in the umbilical arterial (cord) circulation.  In addition, there are often secondary consequences to these perfusion differences; the recipient often has a very large bladder, full of urine, whilst the donor has a collapsed, empty urinary bladder.  

Stage 4. The recipient twin shows signs of severe right-sided heart failure.

Stage 5. This is when sadly one of one twin has already died.