What is Twin-to-Twin Transfusion Syndrome?
Twin-to-twin transfusion syndrome or TTTS, a rare condition affecting identical twins, causes the two fetuses to get unequal blood supply. It can occur at any stage of pregnancy , leading to various congenital defects and even death of one or both twins.
Does Twin-to-Twin Transfusion Syndrome Occur in Fraternal Twins?
It only affects monochorionic twins (twins sharing a single placenta), meaning they have to be monozygotic (derived from the same egg) and identical to be affected by TTTS. Identical twins having separate placentas (dichorionic twins) do not have this condition, even if their placentas implant so close to each other that they may seem to have fused together .
Twin-to-Twin Transfusion Syndrome Mechanism
Identical twins or higher multiples sharing the same placenta have blood vessels within the placenta connecting their blood supplies. In TTTS, one twin (the donor) pumps too much blood to the other twin (the recipient), causing the second twin to have excessive blood while the first one has too little. As a result, the recipient twin produces higher than normal amounts of urine , which may lead to an enlarged bladder, excessive amniotic fluid (polyhydramnios), hydrops, cardiac strain, heart enlargement and prenatal heart failure. On the other hand, the donor twin produces extremely low amounts of urine which may result in dehydration , low amniotic fluid levels (oligohydramnios) and constriction or absence of bladder.
What are the Stages of Twin-to-Twin Transfusion Syndrome?
Fetal surgeon Dr. Ruben Quintero proposed the following staging system, based on the ultrasound and clinical criteria , for classifying the severity of TTTS:
|Stage||Oligohydramnios (donor)/ Polyhydramnios (reciever)||Absence of bladder in donor (on ultrasound)||Doppler ultrasound showing blood flow abnormalities in both twins||Ascites (fluid accumulation in peritoneal cavity), scalp edema , pericardial or pleural effusion, excessive hydrops||Death of one or both fetuses|
Other staging systems have also been proposed as the Quintero one does not provide any information about the prognosis. Depending on the time of occurrence and nature of progression, twin-twin transfusion syndrome is sometimes classified as:
- Acute TTTS : Progresses quickly, generally after the 30th week of pregnancy, without significant warning signs. It may even occur during labor (in vaginal birth) or after clamping the umbilical cord of one baby.
- Chronic TTTS: The common form of transfusion, occurring gradually over time with distinct signs and symptoms visible on ultrasound findings. These cases are generally diagnosed between the 15th and 20th week of pregnancy.
What Causes Twin-to-Twin Transfusion Syndrome?
Researchers are still trying to find the exact causes responsible for this condition as no genetic or environmental factors are known to play any role in its occurrence . The complication does not occur from anything the mother did or did not do before or after conception. It is believed to result from a random placental abnormality as no hereditary or maternal condition has been found to be responsible either.
What are the Symptoms of Twin-to-Twin Transfusion Syndrome?
- Braxton Hicks contractions
- Rapid weight gain
- Abdominal and back pain
- Enlarged belly for a certain gestational age 
- Abdominal tightness
- Feeling of excessive abdominal pressure
- High blood pressure 
- Smaller size compared to the other twin 
- Large size compared to the other twin 
- Redness due to excessive blood
- Increased blood pressure
Inequality between the sizes of identical twins is known as discordant twins .
How to Prevent Twin-to-Twin Transfusion Syndrome?
It is not possible to prevent TTTS due to its unknown etiology. Experts recommend following certain measures that may reduce the risk of the complication:
- Maintaining a proper healthy diet prior to and during pregnancy 
- Taking prenatal supplements recommended by one’s doctor
- Attending prenatal appointments regularly for monitoring the procession of pregnancy
How is Twin-to-Twin Transfusion Syndrome Diagnosed?
The most essential step for evaluating a twin or triplet (or higher) pregnancy for TTTS is to find out if the twins are sharing a single placenta . Determining the fetal sizes and amniotic fluid levels around each baby also helps with the diagnosis.
Fetal Ultrasound – Ultrasound imaging is the best diagnostic method for detecting the syndrome, especially between the 14th and 22nd week of pregnancy . Its purposes include:
- Evaluating the amniotic fluid levels around each twin
- Eliminating any structural deformities in the twins
- Confirming the location of the placenta
- Assessing the insertion of the umbilical cord into the placenta
- Assessing the membrane separating the twins
Fetal Echocardiogram (ECHO) – It is used for:
- Assessing the development and functioning of the hearts of both the twins
- Detecting any cardiac abnormalities in the recipient twin
Amniocentesis – Involves collecting an amniotic fluid sample from the mother for:
- Assessing the development of various internal organs
- Ruling out chromosomal abnormalities in the twins (genetic amniocentesis)
It is not used unless the above tests fail to confirm the diagnosis.
Other diagnostic tests performed for assessing the condition in the infants after birth :
- Complete blood count
- Comprehensive metabolic panel for determining electrolyte balance
- Blood clotting studies such as partial thromboplastin time (PTT) and prothrombin time (PT)
- Chest x-ray
Twin-to-Twin Transfusion Syndrome Differential Diagnosis
- Uteroplacental insufficiency
- Abnormalities in cord insertion causing growth disturbances
- Preterm premature rupture of membranes (PROM) of one twin
- Discordant structural or chromosomal abnormalities of one twin
- Intrauterine infection 
- Hydrops Fetalis
- Polycythemia (increased RBC count)
- Oligohydramnios or Polyhydramnios 
- Anemia of the newborn
Twin-to-Twin Transfusion Syndrome Treatment and Management
The treatment depends on the severity of the condition and the time of diagnosis.
Management of Mild TTTS
Mild cases do not usually require surgical intervention. Management of such cases involves close monitoring of the fetal development using fetal ultrasound and echocardiography . Regular monitoring allows doctors to address any sign of aggravation of the disorder as soon as possible. Complete bed rest along with proper nutritional therapy is often prescribed to the mother for managing the condition and preventing it from worsening.
Amnioreduction (Removal of Excess Amniotic Fluid)
Draining the excess amniotic fluid from the amniotic sac of the recipient twin may help to improve the blood flow. It may also provide temporary relief to the mother .
Fetoscopic Laser Treatment
One of the most common treatment options for severe TTTS, the invasive surgery involves making a small incision in the mother’s belly for monitoring and permanently disconnecting some of the blood vessels connecting the twins. This helps to halt the progression of the disorder by stopping the blood transfusion from the donor twin to the recipient twin .
It involves making a small hole in the intervening amniotic membranes of the twins (with an amnioreduction needle) to equalize the fluid levels in the two amniotic sacs .
In extremely severe cases, doctors may recommend an invasive surgery to stop the blood supply to the dying twin so that the other twin may be better provided for . Selective feticide is not considered unless doctors find it to be the only way for avoiding losing both twins. It helps to reduce the risk of neurologic impairment and death in the remaining twin.
Delivery of the Twins
The doctor may recommend inducing labor or a c-section delivery as soon as the organs of the babies are developed enough to function on their own . This may help to reduce the chances of various complications.
Twin-to-Twin Transfusion Syndrome Prognosis
Untreated cases of severe TTTS often have a poor outcome as it is associated with 90% mortality rate. The surviving twins run a 15% to 50 % risk of various long-term neurologic complications (e.g. cerebral palsy, mental retardation, hearing loss and vision loss) . However, modern treatment procedures have improved the survival rate significantly, lowering the risks of neurological handicaps. The outcome of laser surgery varies greatly with the survival rate for one/both twins being around 91%.
Twin-to-Twin Transfusion Syndrome Complications
- Premature labor due to induction or ruptured membranes
- Premature rupture of the membranes 
- Placental abruption
- Maternal mirror syndrome (mother having the same symptoms as the sick fetus) 
- Anemia in donor twin
- Neurologic sequelae in the surviving twin due to death of the other twin 
- Brain damage in the receiver twin
- Respiratory, heart and digestive defects in the receiver twin due to high amniotic fluid levels 
- Fetal death
Twin-to-Twin Transfusion Syndrome Incidence
Statistics show it to occur in around 15% of identical twin pregnancies .
Twin-to-Twin Transfusion Syndrome Foundation
The Twin to Twin Transfusion Syndrome Foundation
411 Longbeach Parkway
Bay Village, Ohio 44140
Phone: 1-800-815-9211 / 440-899-8887
Email: [email protected]
Twin-to-Twin Transfusion Syndrome ICD-9 and ICD-10 Codes
ICD-9 codes used for twin-twin transfusion syndrome are 762.3, 772.0
ICD-10 codes for twin-to-twin transfusion syndrome are O43.0, P02.3, P50.3
- References +
fetal-diagnosis-and-treatment/ fetal-diagnoses/twin-twin- transfusion-syndrome-ttts.html
cincinnatichildrens.org/ service/f/fetal-care/ conditions/twin-twin- transfusion-syndrome/
health/guides/disease/fetal- transfusion-syndrome/overview. html#Symptoms
health/twin-to-twin- transfusion-syndrome?# Prevention
specialties/obgyn/maternity/ prenatal/perinatal/multiples/ fetalsurgery/ttts/Pages/ default.aspx
coloradofetalcarecenter.org/ conditions/twin-to-twin- transfusion-syndrome/diagnosis
intr5/c6700/OBGYN/f/web/Twin% 20to%20Twin%20transfusion% 20syndrome/index.htm
org/Health-Topics/Womens- Health/Twin-to-twin- transfusion-syndrome/
health/twin-to-twin- transfusion-syndrome?# Treatment