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. Stage III: In addition to the characteristics of Stages I and II, there is abnormal blood flow in the umbilical cords of the twins. Stage IV: In addition to all of the above findings, the recipient twin has swelling under the skin and appears to be experiencing heart failure (fetal hydrops). Stage V: In addition to all of the above findings, one of the twins has died. This can happen to either twin. The risk to either the donor or the recipient is roughly equal & is quite high in Stage II or higher TTTS. The Quintero staging does not provide information about prognosis, and other staging systems have been proposed. Treatment Various treatments exist for TTTS. Non treatment This is equivalent of zero intervention. It has been associated with almost 100% mortality rate of one or all fetuses. Exceptions to this include patients that are still in Stage 1 TTTS and are past 22 weeks' gestation. Adjustment of amniotic fluid Serial amniocentesis This procedure involves removal of amniotic fluid periodically throughout the pregnancy under the assumption that the extra fluid in the recipient twin can cause preterm labor, perinatal mortality, or tissue damage. In the case that the fluid does not reaccumulate, the reduction of amniotic fluid stabilizes the pregnancy. Otherwise, the treatment is repeated as necessary. There is no standard procedure for how much fluid is removed each time. There is a danger that if too much fluid is removed, the recipient