Twin To Twin Transfusion Syndrome is a disease which affects twin or higher order multiple pregnancies where one or more babies share a common placenta.
It is caused by abnormalities in the interconnecting blood vessels in the placenta which supply blood to each baby via their umbilical cords. These abnormalities cause the blood supply to be uneven, which means that one baby gets too much blood and the other does not get enough.
The baby who is not getting enough blood and nutrients is known as the donor baby. As a result, the donor baby has a reduced volume of blood, and so grows at a slower rate than his or her twin. The amount of amniotic fluid, which is determined by the amount of urine the baby outputs, is also reduced leading to oligohydramnios or a "stuck baby" - a baby with little or no amniotic fluid around it.
The baby who is getting too much blood and nutrients is known as the recipient baby. As a result, the recipient baby has an increased volume of blood and so grows at a much faster rate than his/her twin. He or she also has an increased rate of urine output resulting in polyhydramnios or excess amniotic fluid. The increased blood supply also puts strain on the recipient baby's heart and can potentially cause heart failure.
The outcomes for twins affected by TTTS depend on how severely they are affected and at what point during the pregnancy TTTS develops. An ultrasound to determine whether your twins share a placenta or have separate placentas will be carried out during the first trimester or early second trimester. If your twins have separate placentas they are at no risk of TTTS. If your twins share a placenta you will have fortnightly ultrasounds to monitor your babies' growth and ensure that they are growing at similar rates.
Symptoms of TTTS include rapid growth in the size of your belly, excessive swelling in your hands and feet, a sudden increase in body weight and extreme discomfort caused by excess amniotic fluid. On ultrasound, twins with TTTS will have discordant (uneven) growth, there will be a marked difference in the amount of fluid around each baby, and blood flow studies will indicate an uneven supply of blood through each umbilical cord.
If TTTS is suspected, treatment depends on how far into your pregnancy you are. If you are more than 26 weeks pregnant it is likely that your babies will be delivered by caesarian section as the risks associated with TTTS outweigh the risks associated with premature delivery.
If you are less than 26 weeks pregnant, you have a number of options which your LMC will discuss with you. Some, such as laser surgery, address the abnormalities in the placenta, whilst others, such as draining of amniotic fluid using a long needle address the issues of uneven fluid distribution. If it is suspected your babies have TTTS you will be referred to a specialist with expertise in this area. TTTS babies are almost always delivered by caesarian section as this is considered safest for them.