Twin-to-twin transfusion syndrome affects identical twins due to a problem with the placenta, causing one twin to receive most of the blood flow while the other receives less. Advances in obstetrics now allow most twins to survive the condition, with treatments including amniocentesis and laser surgery. The condition is not a birth defect, hereditary, or caused by the parents’ actions. Lingering health problems can occur, including respiratory, digestive, or heart defects, anemia, and developmental delays.
Twin-to-twin transfusion syndrome is a problem affecting unborn identical twins due to a problem with the placenta. In normal twin pregnancies, the two fetuses are able to share the placenta, the organ that helps nourish the growing fetus through the mother’s blood supply. In most cases of twin-to-twin transfusion syndrome, one twin receives most of the placenta’s blood flow, while the other twin receives much less than her share. While the results were once devastating for the mother and her family, advances in obstetrics now allow most twins to survive the condition.
TTTS is a random event, affecting approximately 15% of identical twin pregnancies. Each fetus in a fraternal twin pair has its own placenta, so this condition is not a problem for fraternal twins. Twin-to-twin transfusion syndrome is not a birth defect; it is not a matter of heredity – genetics do not play a role – and it is not the result of the parents’ actions or inactions.
In twin-twin transfusion syndrome, each twin tries to adjust to his or her situation. The twin who is not getting blood flow tries to conserve water and energy. This causes a condition called oligohydramia or low amniotic fluid volume. The other twin, the one receiving more than his quota of blood, tries to rid himself of the increased fluid through increased urination, a condition known as polyhydramnios.
A mother whose pregnancy is affected by twin-to-twin transfusion syndrome may see a growth spurt in her womb. Your uterus may be large by your due date, you may gain weight much faster than normal, and your hands or legs may swell in early pregnancy. A doctor looking at an ultrasound can see evidence of a shared placenta.
There are two types of twin-to-twin transfusion syndrome: acute and chronic. Chronic TTTS is more common and occurs gradually; it is often diagnosed during a routine ultrasound. If this happens, the doctor usually prescribes bed rest and a nutritional program for the mother. Acute TTTS occurs without warning after the 30th week of pregnancy. It can also happen during a vaginal birth or after a twin’s cord has been clamped.
Until recently, TTTS often claimed the lives of both twins, but two treatments are now available. Amniocentesis can be used to drain excess fluid, which improves blood flow to the placenta and reduces the risk of preterm birth. This method can prevent fatal crashes about 60 percent of the time. Laser surgery can be used in extreme cases. If the babies are mature enough to survive on their own, a doctor may choose to deliver them early.
Less than ideal conditions in the womb mean that babies with twin-to-twin transfusion syndrome can have lingering health problems. The twin who has received too much blood may have respiratory, digestive or heart defects due to excess fluids; the twin who has received too little blood can develop anemia. If twins are delivered prematurely, there may also be developmental delays.
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