Twin-to-twin transfusion syndrome (TTTS), also known as feto-fetal transfusion syndrome (FFTS), twin oligohydramnios-polyhydramnios sequence (TOPS) and stuck twin syndrome, is a complication of monochorionic multiple pregnancies (the most common form of identical twin pregnancy) in which there is disproportionate blood supply between the fetuses. This leads to unequal levels of amniotic fluid between each fetus and usually leads to death of the undersupplied twin and, without treatment, usually death or a range of birth defects or disabilities for a surviving twin, such as underdeveloped, damaged or missing limbs, digits or organs (including the brain), especially cerebral palsy.The condition occurs when the vein–artery connections within the fetuses shared placenta allow the blood flow between each fetus to become progressively imbalanced. It usually develops between week 16 and 25 of pregnancy, during peak placental growth. The cause of the developmental effects on a surviving fetus may include necrotic embolisms from a dead fetus, low blood volume due to pooling in the dead fetus or velamentous cord insertion (insertion of the umbilical cord into the chorioamniotic membranes).The primary treatment of TTTS is fetoscopy and laser ablation of the interconnecting blood vessels to cut off the exchange of blood between the fetuses. This treatment is associated with an 85% survival rate of at least one fetus. Other treatments include periodic removal of amniotic fluid (serial amniocentesis), which is associated with a 66% survival rate of at least one fetus. Without treatment, there is an almost 100% mortality rate of one or all fetuses.
Complications include gangrenous limbs, hands and feet, cerebral palsy and IQ deficits, constriction rings of limbs and digits, reduced digits, skin defects, brain cysts, hydranencephaly, multicystic encephalomalacia, microencephaly, renal agenesis and bowel atresia. There are three hypotheses explaining these complications. Embolic Theory: The demise of the donor twin allows necrotic tissue, presumably thrombosis-plastin like material, to pass through the vasculature of the surviving twin via the placental vessels. The necrotic tissue embolizes the surviving twins mesenteric artery, resulting in bowel atresia, the renal artery, resulting in renal agenesis, or the peripheral arteries, resulting in limb ischemia and skin abnormalities. Ischemic Theory: The demise of the donor twin creates a low-pressure state resulting in the shunting of blood into the low-resistance vascular system of the dead fetus. This state of low pressure acutely causes hypovolemia, resulting in ischemia and poor end-organ perfusion. Placentation Theory: The incidence of velamentous cord insertion, an abnormal insertion of the umbilical cord into the placenta, is higher in TTTS. The exact mechanism of effect this has on fetal damage is unknown. Diagnosis
Quintero stages
A staging system is commonly used to classify the severity of TTTS.Stage I: A small amount of amniotic fluid (oligohydramnios) is found around the donor twin and a large amount of amniotic fluid (polyhydramnios) is found around the recipient twin. Stage II: In addition to the description above, the ultrasound is not able to identify the bladder in the donor twin.