If non-identical twins are born from two totally different zygotes (fertilised eggs), identical twins form by the splitting of one zygote (fertilised egg) into two foetuses. Problems can arise when the splitting takes place between four and eight days after the egg is fertilised.
What results due to such delayed splitting is that two amniotic sacs containing one foetus each are found inside one placenta. While 85 per cent of such foetuses go on to full term of development and are born as healthy infants, complications can arise in the remaining 15 per cent.
Two foetuses sharing the same placenta will by default have vascular connections between them. Blood flows from foetus A to foetus B and back to foetus A. This is the case with 85 per cent of identical twins.
But in the remaining 15 per cent (where complications arise), the blood flowing from foetus A to foetus B never returns to foetus A from foetus B. “This is because the returning blood vessels from foetus B to foetus A are either absent or deficient,” says Dr. S. Suresh, Director of the Chennai-based Mediscan. He is also an adjunct professor at the Tamil Nadu Dr. M.G.R. Medical University, Chennai.
Unequal blood availability in the two foetuses is the central issue. “Since blood gets accumulated in foetus B, the foetus tends to pour out plenty of fluid (urine), which then gets collected around the foetus quite rapidly,” Dr. Suresh explains. “Foetus A, on the other hand, suffers from blood deficiency, less urine and less fluid in the amniotic sac.”
This is called the Twin Twin Transfusion Syndrome (TTTS). “If untreated, there is nearly 100 per cent chance of losing both the babies due to premature delivery,” he warns. “The best form of treatment is fetoscopy.”
In the case of fetoscopy, a 2 mm diameter fetoscope is inserted into the amniotic sac and all the blood vessels between the two foetuses are burned using a laser.
“All the vessels have to be burnt, else the flow can always reverse,” he says. “Once the blood supply is cut, each foetus has its own circulation through the placenta.”
Seven deliveries so far
Usually 7 to 8 blood vessels exist between the foetuses. “The largest number we have seen is 13,” he says.
He should know better as he and his team, Dr. Indrani Suresh and Dr. Uma Ram, have done 13 fetoscopies to save identical twins suffering from Twin Twin Transfusion Syndrome during the last 15 months. Of the 13 cases, seven women delivered healthy babies.
In the absence of medical intervention in the form of fetoscopy, the chances of both the twins dying due to premature delivery are high. This is particularly so when the TTTS is at stage 2 and above.
“Treatment is required when it is stage 2 as the chances of premature birth is high,” he says. “One foetus has more fluid and the other has less.”
There are five stages of TTTS and it can progress from one stage to another quite quickly. “Some may not progress from one stage to another. So they need close expert monitoring,” he says.
TTTS has its own risk, though. “There is 15 per cent chance of miscarriage due to the intervention,” he cautions.
If it costs about 6 lakhs to 7 lakhs when done abroad, Mediscan charges just Rs.80,000 for the procedure.