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Twin-to-twin transfusion syndrome (TTTS, also known as Feto-Fetal Transfusion Syndrome (FFTS) and Twin Oligohydramnios-Polyhydramnios Sequence (TOPS)) is a complication with high morbidity and mortality that can affect identical twin or higher multiple pregnancies where two or more fetuses share a chorion and hence a single placenta, but have separate amniotic sacs. Severe TTTS has a 60-100% mortality rate.[1]
TTTS occurs in approximately 5.5-17.5% of all monochorionic pregnancies. [2] Based on 2003 CDC data, the theoretical incidence of TTTS would be 1.38 to 1.86 cases in every 1,000 live births or an estimated near 7,500 cases each year in the United States. One Australian study, however, noted an occurrence of only 1 in 4,170 pregnancies or 1 in 58 twin gestations. This distinction could be party explained by the “hidden mortality” associated with MC multifetal pregnancies–instances lost due to premature rupture of membrane (PROM) or intrauterine fetal demise before a thorough diagnosis of TTTS can be made [3]
As a result of sharing a single placenta, the blood supplies of monochorionic twin fetuses can become connected, so that they share blood circulation: although each fetus uses its own portion of the placenta, the connecting blood vessels within the placenta allow blood to pass from one twin to the other. 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 twin is increased, which can strain the fetus’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 fetuses to die, or lead to severe disabilities. If TTTS develops after 26 weeks, the babies can usually be delivered alive and have a greater chance of survival without disability.
Other than requiring a monochorionic-diamniotic twin (or higher multiple) pregnancy, the causes of TTTS are not known. It is not known to be hereditary or genetic.
Some doctors recommend complete bed-rest for the mother coupled with massive intakes of protein (generally in the form of “protein shakes” such as Boost or Ensure) as a therapy to try to counteract the syndrome. Theories for why this would be effective vary, but some doctors claim to have seen it help. There are, however, no formal clinical trials indicating that the bed rest / high-protein diet is effective.
Research into TTTS is ongoing and best medical practices change quickly with respect to this condition. For the most up-to-date information, consult with a maternal-fetal medicine specialist.
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