This little known condition occurs in the 1 in 400 pregnancies with identical twins  who share their blood flow inside the womb. If the share through their single placenta is uneven, this may cause death or brain damage. TTTS affects around 600 babies per year in the UK. The larger twin cannot cope with too much blood and gets heart failure, and the smaller twin is starved of blood and oxygen. Despite advances in treatment, around 40% of babies still die, and 10% of survivors are handicapped for live.

Our research over the last decade has shown that the pattern of blood vessel connections in the placenta determines which pregnancies develop TTTS. This has led to a new Doppler test to predict TTTS, and has helped us understand how severe TTTS causes brain injury and interferes with heart development, a prerequisite to preventing these complications. The safety of telescopic laser and drainage therapies has greatly improved, thanks to research showing precisely which blood vessels cause the problem. This has helped pinpoint exactly which patients benefit from which treatment, with mild cases spared the complications of the more risky therapies reserved for severe cases. Several new treatments have been introduced for other twin transfusion problems including early delivery, drugs to control excess amniotic fluid, and techniques to block blood flow.

A key to improving outcome in this devastating condition is careful monitoring of twin pregnancies. The earlier the condition is picked up through poor growth of one twin or a build-up of fluid in the other, the earlier TTTS can be treated and thus the better the outcome.

Although a large number of lives have been saved already, there is still a long way to go. Despite the progress, two-thirds of parents with a TTTS pregnancy still end up with at least one dead or brain-damaged baby. The focus for the next decade is to build on our results, both by improving current treatments and by developing new ones.

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