Twin-to-twin transfusion syndrome (TTTS, also known as Feto-Fetal Transfusion Syndrome (FFTS) and Twin Oligohydramnios-Polyhydramnios Sequence (TOPS)) is a disorder that can affect identical twin or higher multiple pregnancies where two or more foetuses share a common (monochorionic) placenta.

As a result of sharing a single placenta, the blood supplies of the fetuses can become connected, so that the foetuses essentially shares a single blood supply. Depending on the number, type and direction of the interconnecting blood vessels (anastomoses), blood can be transferred disproportionately from one twin (the "donor") to the other (the "recipient"). The transfusion causes the donor twin to have decreased blood volume, retarding the donor's development and growth, and also decreased urinary output, leading to a lower than normal level of amniotic fluid (becoming oligohydramnios). The blood volume of the recipient is increased, which can strain the donor's heart and eventually lead to heart failure, and also higher than normal urinary output, which can lead to excess amniotic fluid (becoming polyhydramnios).

In early pregnancy (before 26 weeks), TTTS can cause both foetuses to die, or lead to severe disabilities. If TTTS develops after 26 weeks, the babies can usually be delivered and have a greater chance of survival without disabilty.

Other than requiring a monochorionic twin (or higher multiple) pregnancy, the causes of TTTS are not known, and its incidence ie believed to be random. It is not hereditary or genetic.

TTTS was first described by a German obstetrician, Friedrich Schatz , in 1875. TTTS can be treated by surgery during pregnancy, using foetoscopy to find the interconnecting blood vessels, and a laser beam to coagulate the blood in these vessels, blocking them. This is called foetoscopic laser ablation, and is only performed in a few hospitals worldwide. TTTS is believed to affect roughly 1 in 1000 pregnancies.

See also

• Vanishing twin

External links

• The Twin to Twin Transfusion Syndrome Foundation
• The UK Twin to Twin Transfusion Syndrome Association