Introduction
Twin-to-twin transfusion (TTTS) is a disease or an abnormality of the placenta that affects the health of each twin in a different way. The condition is rare but severe and only occurs in identical twins with a common placenta. The single placenta passes through both the twins and contains blood vessels which usually carry a balanced blood supply to both babies. However, in the case of twin-to-twin transfusion, this balance is disturbed as the blood flows from one twin (donor twin) to the other (recipient twin). This leads to an unequal blood exchange and thus can cause a risk of heart failure, the oversize of the recipient twin, and the accumulation of excess amniotic fluid around this twin. On the other hand, the donor twin is smaller due to a lack of enough blood, and also it produces very little urine, which makes the bladder invisible on the ultrasound. There are treatment options available for twin-to-twin syndrome, but if the condition is left untreated, the survival rate of twins may decrease to less than 10 percent.
What Are the Causes of Twin-to-Twin Transfusion?
The exact cause of twin-to-twin transfusion syndrome is unknown. It is an irregularity of the placental that occurs during gestation and is a congenital defect. The syndrome arises due to the blood movement from one twin to the other through the common placenta. As a result, the twin that receives the blood supply is called the recipient twin, and the one that loses the blood is known as the donor twin. This causes an imbalance in the blood flow between the twins, which is usually fairly balanced, and thus causes twin-to-twin transfusion syndrome (TTTS).
What Are the Symptoms Shown by the Mother in the Case of Twin-to-Twin Transfusion?
The mother usually experiences symptoms because of the excess of amniotic fluid accumulation around the recipient twin. The symptoms include
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Pressure in the stomach.
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Breathlessness.
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Rapid weight gain.
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Premature contractions.
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The rapid expansion of the abdomen or tightness in the abdomen.
How to Diagnose Twin-to-Twin Transfusion?
The doctor can diagnose twin-to-twin transfusion during a regular prenatal ultrasound. The condition can occur at any time during the pregnancy and is more severe during the early phase of pregnancy when delivery is impossible. The doctor conducts various diagnostic tests for suspected problems during routine checkups and ultrasounds. The pediatric cardiologist performs a special ultrasound test called a fetal echocardiogram to check a fetus’s heart and blood vessels carefully.
The ultrasound findings suggest that suggest pregnancy needs to be closely monitored as follows:
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Same-gender twins.
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Differences in size in twins.
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Single placenta.
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A dividing membrane that is thin and not clear.
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Excess of amniotic fluid or polyhydramnios in one of the twin’s sacs.
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Decreased or no amniotic fluid or oligohydramnios in the other twin’s sac.
In addition, fetal MRI (magnetic resonance imaging) is also performed to look for any injury to the brain that may be caused due to twin-to-twin transfusion syndrome (TTTS).
The severity of TTTS is further diagnosed with the Quintero staging system on a scale of one to five, where five is the most severe form.
Staging of Twin-To-Twin Transfusion Syndrome:
- Stage I: There is a major difference in the amniotic fluid levels. One twin has an excess of fluid, and the other has very less fluid in the sac.
- Stage II: The bladder of the donor twin is not visible on the ultrasound in stage II and the difference in amniotic fluid levels also persists.
- Stage III: This stage is marked by an abnormal blood flow through the blood vessels or umbilical cord around the heart of one or both twins, along with an empty donor bladder and abnormal amniotic fluid levels.
- Stage IV: In this stage, fetal hydrops are formed along with the above abnormalities. Fetal hydrops is the collection of amniotic fluids in body cavities in one or both twins.
- Stage V: Loss or death of one or both twins.
The severity of the recipient babies’ heart condition is also evaluated through fetal electrocardiogram and marked as mild, moderate, or severe.
How Is Twin-to-Twin Transfusion Treated?
There are very few options available to treat twin-to-twin transfusion syndrome. Therefore, the doctor suggests fetal intervention methods only in the most severe cases. In some cases, if the TTTS occurs during the third trimester, premature delivery is the suggested option rather than fetal intervention, as it can cause complications in the pregnancy. The treatment plans are as follows:
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Monitoring the Pregnancy: Less severe cases do not require surgical intervention, and the fetus is monitored with ultrasounds and electrocardiograms. In case of any worsening condition, the best treatment plan or early delivery is usually planned depending on the stage of pregnancy and severity of the condition (TTTS).
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Amnioreduction: In this method, the excess of amniotic fluid is drained from the recipient fetus’s sac if the twins are not severely affected by twin-to-twin transfusion. If the amnioreduction method is ineffective, the doctor suggests laser surgery, also known as selective fetoscopic laser photocoagulation (SFLP).
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Laser Surgery: This method is also known as selective fetoscopic laser photocoagulation. A small incision is made in the mother’s abdomen up to the uterus with a small metal tube or trocar. The fetoscope is then passed through this metal tube to view the shared placenta and other blood vessels on the placental surface.
What Is the Differential Diagnosis for Twin-to-Twin Transfusion?
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Premature rupture of membranes (PROM).
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Amniotic fluid discrepancies.
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Selective fetal growth restriction (SFGR).
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Preterm premature rupture of membranes (PPROM).
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Twin anemia.
Conclusion
Twin-to-twin transfusion syndrome is a rare prenatal condition affecting twins' growth rates due to unequal placental blood supply. The condition does not occur due to anything related to the mother in any way. Almost 70 percent of identical twins have a shared placenta, and 15 to 20 percent of such pregnancies are usually affected by twin-to-twin transfusion syndrome. TTTs cases that are not treated timely during gestation cause 90 % fatality of twins after delivery, and almost 15 % to 50 % of them are at risk of developing neurological disorders. Therefore, the doctor's timely intervention is important to avoid future complications in the pregnancy.
