Twin-to-twin transfusion syndrome (TTTS) is a condition where there is an imbalance of blood flow across blood vessels.
This means one twin will have more blood, causing it to grow bigger and have more amniotic fluid around it.
The other twin will receive less blood, causing it to be smaller and have less fluid.
The recipient twin may receive too much blood for its heart to handle, while the donor twin may receive too little blood to enable proper growth in the womb.
If left untreated, up to 90 per cent of twins with TTTS may not survive, said Associate Professor Mahesh Choolani, senior consultant at the National University Hospital (NUH) Women's Centre.
She called TTTS, which occurs in one in 1,600 pregnancies, a relatively rare pregnancy complication.
It affects about 15 per cent of monochorionic diamniotic (MCDA) twins - identical twins where the foetuses share a placenta, but have their own amniotic sacs.
MCDA twins make up two-thirds of all identical twins.
TTTS can be detected during ultrasound scans.
Dr Wee Horng Yen, a Singaporean obstetrician and gynaecologist at O & G Care Clinic, said twin pregnancies are scanned in the first trimester to determine if the foetuses share a placenta (also known as monochorionic).
In monochorionic twin cases, the mother will have to go for frequent scans to detect if there is a possible onset of TTTS, he said.
The prenatal condition can be treated with laser photocoagulation, which blocks the blood vessels that communicate between the two foetuses.
This stops the blood flow between the twins - much like separating the placenta - allowing each twin to develop independently.
NUH started using laser photocoagulation last year to treat TTTS, a method that Prof Choolani said raises the survival rate of affected twins.
"With laser treatment, up to 85 per cent of at least one of the twins can survive. In the five cases we have treated (with laser) so far, eight out of the 10 babies were born alive," she said.
Source: TNP Singapore