TWIN PREGNANCY AND TWIN TRANSFUSION SYNDROME: RISKS, CAUSES, AND TREATMENT
Medically Reviewed by Dr. Sony Sherpa (MBBS)
Twin to Twin Transfusion Syndrome (TTTS) is an infrequently reported, serious condition that can occur in identical twin pregnancies. It is a condition where one twin receives more blood flow and nutrients from the placenta than the other, resulting in an imbalance in the growth and development of the twins.
This article will explore the latest advances in TTTS treatment, as well as the risk factors, causes, diagnosis, types, symptoms, and long-term effects of TTTS.
What is Twin to Twin Transfusion Syndrome?
TTTS can only develop in identical twins (monozygotic twins) who share a placenta, which supplies blood, oxygen, and nutrients to both developing fetuses. It occurs when an imbalance in blood flow and nutrient supply exists between the twins. This results in one twin (the recipient twin) receiving more than the other twin (the donor twin). TTTS can lead to severe complications for both twins if left untreated.
The types of TTTS depend on the type of twin pregnancy. Most pregnancies involve a single zygote developing into one baby. However, in twin pregnancies, twins can be monozygotic (identical) or dizygotic (fraternal).
Monozygotic (identical twins): In the case of identical twins, one fertilized egg splits into two individual embryos very early in development[1]. These twins share all their genes and will be the same sex. The timing of the split determines how the placenta and amniotic sacs develop, leading to the different types of monochorionic (one placenta) twin pregnancies. An average of 33% of twin births are monozygotic, with the remainder being dizygotic.
There are two types of TTTS, based on the type of identical twin development in utero[2]: Monochorionic Diamniotic (MCDA) and Monochorionic Monoamniotic (MCMA).
- MCDA: This is the most common type of TTTS and identical twin pregnancy, occurring in about 75% of monozygotic twin births. The twins share a placenta and have their amniotic sacs of this type. MCDA TTTS affects approximately 8-10% of twins born with MCDA.
- MCMA: This is a rarer type of TTTS, occurring in about 6% of cases. In this type, the twins share both a placenta and an amniotic sac.
Dizygotic (fraternal twins): Two separate eggs are released by the ovaries and fertilized by two sperm cells. These twins will have unique genetic makeups and can be the same or different sexes. Fraternal twins always have separate placentas and amniotic sacs (dichorionic diamniotic - DCDA).
Can Fraternal Twins Have Twin-to-Twin Transfusion Syndrome?
Fraternal twins cannot develop TTTS as they do not share a placenta or amniotic sacs.
How Rare Is Twin To Twin Transfusion Syndrome?
The prevalence of TTTS is not known. Estimates indicate that it occurs in approximately 1-3 twin births per 10,000, of which twin births comprise 2-4% of all live births worldwide.
TTTS Causes and Risk Factors
The exact cause of TTTS is still unknown, yet it is believed to result from abnormal blood vessel connections in the shared placenta. This leads to an unequal allotment of blood flow and nutrients between the twins, leading to complications such as swelling and organ stretching in the recipient twin and lower blood perfusion and kidney complications in the donor twin.
In TTTS, there is an imbalance between blood vessel types in the placenta, contributing to uneven blood flow between twins. Some blood vessels allow blood to flow in one direction, while others enable bidirectional flow. The ones that allow bidirectional flow may help protect against TTTS, while the ones with unidirectional flow increase the risk. This observation is also why TTTS rates are higher in MCDA twins than MCMA, as MCDA twins have more unidirectional blood vessels on average.
Various risk factors elevate the chances of developing TTTS, including:
- Monochorionic twins (twins who share a placenta)
- A large placenta
- A significant difference in the size of the twins
- A history of TTTS in a previous pregnancy
- Advanced maternal age
- Smoking during pregnancy
Symptoms of TTTS and Diagnosis
The symptoms of TTTS can vary depending on the severity of the condition. Some common symptoms found upon examination include:
- A significant difference in the size of the twins, with one twin appearing to be much smaller than the other
- Excessive amniotic fluid in one sac and low amniotic fluid in the other
- A visible difference in the amount of movement of the twins
- A visible difference in the heart rates of the twins
Studies indicate that expectant mothers may experience symptoms[3] such as:
- Abdominal pain, tightness, or contractions
- Sudden increase in body weight
- Swelling in the hands and legs in early pregnancy
- Decreased fetal movement
- Shortness of breath
- Rapid abdominal growth of the womb
To receive a diagnosis for TTTS, the Quintero Staging System is used to determine the severity of the condition. This system has four stages, with stage 1 being the mildest and stages 4 to 5 being the most severe[4].
- Stage 1: Ultrasound shows discordant amniotic fluid volume, with one twin having more than 8 cm of fluid and the other having less than 2 cm. While the bladder of the donor twin is smaller, it is still visible.
- Stage 2: This stage involves monitoring changes in the appearance of the donor twin's bladder, which can indicate worsening conditions. In a repeat ultrasound, after an hour of observation, the donor twin's bladder is no longer visible.
- Stage 3: Blood flow studies show abnormal blood flow in one or both twins. This can include absent end diastolic velocity (AEDD) in the umbilical artery, bumpy positive flow in the umbilical vein, or lacking or backward flow in the ductus venosus.
- Stage 4: One or both babies have gone into heart failure, as evidenced by fluid accumulation (hydrops) around the scalp, chest, or abdomen.
- Stage 5: One or both babies have died.
If you are experiencing the symptoms listed above, it is vital to confer with your doctor immediately. They will complete a series of tests to aid in the diagnosis, including[5]:
- Ultrasound: This is the most common method used to diagnose TTTS. It allows the doctor to see the size and growth of the twins, as well as the amount of amniotic fluid in each sac. During a routine prenatal ultrasound, a healthcare provider may discover TTTS if they notice that one twin has a larger amniotic sac than the other.
- Doppler ultrasound: This test evaluates the blood flow between the twins and can help determine if there is an imbalance. It can show irregularities in the blood flow between the twins.
- Fetal echocardiography (echo): This test uses sound waves to create images of the twins' hearts. Your provider can assess each twin's heartbeat and identify potential abnormalities.
- Amniocentesis: This test concerns the sampling of amniotic fluid from each sac to check for chromosomal abnormalities.
- Fetal MRI: Your provider may request a fetal MRI to get a more detailed picture of the twins and placenta.
- Consultation with a maternal-fetal medicine specialist: A specialist can perform additional tests to assess each twin's blood flow, bladder function, and amount of amniotic fluid. They can also provide expert advice on treatment options.
Early identification and intervention are essential for a successful outcome in TTTS pregnancies. If you have any concerns about your pregnancy, please talk to your doctor immediately.
What is the Difference Between TAPS and TTTS?
Both Twin-to-twin transfusion syndrome (TTTS) and twin-anemia-polycythemia sequence (TAPS) are chronic forms of feto-fetal transfusion in monochorionic twins, which means that the twins share a single placenta.
Each condition can seem similar, with similar symptoms and complications. The key distinction pertains to the presence of amniotic fluid discordance[6]:
- TTTS is characteristic of the twin oligo-polyhydramnios sequence (TOPS), meaning one twin has too little amniotic fluid (oligohydramnios), and the other twin has too much amniotic fluid (polyhydramnios).
- TAPS features larger inter-twin hemoglobin differences without amniotic fluid differences. The twins have no significant disparity in the amount of amniotic fluid that each uses. TAPS may occur in twins suffering from TTTS.
Complications and Long-Term Effects of TTTS
The donor twin experiences[7]:
- Progressive loss of blood volume (hypovolemia): This can lead to malnourishment and possible organ failure.
- Kidney and Blood Pressure Issues: Low blood volume in the donor twin leads to renal hypoperfusion, activating the renin-angiotensin-aldosterone system (governing fluid balance) and affecting prenatal development.
- Urination decreases: Because the donor twin receives less blood, the kidneys do not have to filter as much fluid from the blood, and urination decreases. This can lower amniotic fluid levels, which otherwise act as a cushion in the womb that aids in developing the fetal respiratory, urinary, and gastrointestinal systems.
- Atherosclerosis Risk: The donor twin may show vascular changes arising from increased collagen synthesis and blood vessel wall growth.
The recipient twin is at risk for:
- Increased blood volume (hypervolemia): This can lead to increased urination, more frequent bladder filling, and the production of more significant amounts of urine.
- Polyhydramnios: An abnormal increase in amniotic fluid can strain the recipient's heart, causing it to swell and stretch. This also triggers the release of atrial natriuretic peptide and brain natriuretic peptide. Either of these can increase the risk of cardiomyopathy and central nervous system disorders later in life.
- Cardiovascular complications: Recipient twins may exhibit heart valve insufficiency, blood pressure problems, arrhythmia, and respiratory complications due to a narrowing of the pulmonary artery (stenosis).
If left untreated, TTTS can lead to severe complications for both twins, including:
- Premature birth
- Low birth weight
- Brain damage
- Heart problems
- Lung problems
- Developmental delays
- Cerebral palsy
In addition, TTTS can also have long-term effects on the twins, including:
- Learning disabilities
- Vision and hearing problems
- Motor skill impairments
- Behavioral issues
The condition can be potentially life-threatening to one or both twins if left untreated.
Twin To Twin Transfusion Syndrome Survival Rate
The survival rate for twins with TTTS has remarkably improved in recent years as a result of advancements in treatment options. According to a study issued in the Iranian Journal of Medical Sciences, the overall survival rate for twins with TTTS is around 70%.
Twin To Twin Transfusion Syndrome Treatment
The treatment for TTTS depends on the severity of the condition and the stage of the diagnosis.
In the past, the only treatment option was to deliver the babies prematurely. If the TTTS is not severe, this approach is ideal. However, in moderate to severe instances, it often leads to serious complications for the twins.
With advancements in medical technology and research, minimally invasive techniques are now available for treating TTTS. These include[8]:
- Laser surgery: This is the most common treatment for TTTS and involves using a laser to shut off the abnormal blood vessels in the placenta.
- Amnioreduction: This procedure involves draining excess amniotic fluid from the sac of the larger twin to reduce the pressure on the smaller twin.
- Selective fetoscopic laser photocoagulation: With this more recent and refined method, the abnormal blood vessels are precisely and selectively sealed off with a laser while observing the blood flow between the twins using a fetoscope.
These treatments can help save one or both twins with a high survival and success rate. They also require specialized care from experts in maternal-fetal medicine. Seeking treatment at centers with experience in managing TTTS provides the best chance for the well-being of both mothers and babies.
After undergoing a procedure for TTTS, frequent follow-up visits are necessary to monitor the health and well-being of the expectant mother. If premature delivery was performed, the infants may require supportive care in a neonatal intensive care unit (NICU).
Latest Advances
Significant progress has been made in managing TTTS over the last decade, with better survival rates and lower complication risks for both twins in most instances.[9]
Further advancements are currently in development, such as:
Minimally Invasive Techniques: Fetoscopic laser surgery is the standard treatment for TTTS. Innovations in this area focus on refining techniques for even greater precision and safety. Smaller instruments, enhanced imaging, and improved targeting systems are all avenues of research designed to decrease the risks and improve the chances of success.[10]
Fetal Monitoring Technologies: Enhanced monitoring before and after surgery is critical to successful TTTS treatment. New non-invasive fetal monitoring tools allow for more continuous assessment of fetal heart rate and well-being, aiding doctors in optimizing the timing of surgical interventions and post-operative care.
Predictive Biomarkers: One key area of research is the identification of biomarkers within maternal blood. A small body of evidence suggests that placental blood yields lower quantities of various metabolites, including fatty acids, organic acids, and liver amino acids[11]. In the future, blood tests will easily detect TTTS and other similar pregnancy-related complications.
Conclusion
Twin Transfusion Syndrome is a rare yet serious condition that can occur in identical twin pregnancies. It is essential to be aware of the risk factors, symptoms, and treatment options for TTTS to ensure the best possible outcome for both twins. With the latest advancements in TTTS treatment and fetal monitoring technologies, the survival rate for twins with TTTS has significantly improved. If you are pregnant with identical twins, it is necessary to consult with your doctor and keep track of the growth and development of your twins to detect any signs of TTTS early on.
To search for the best pediatric healthcare providers in Azerbaijan, Germany, India, Malaysia, Poland, Singapore, Spain, Thailand, Turkey, the UAE, the UK and The USA, please use the Mya Care Search engine.
To search for the best healthcare providers worldwide, please use the Mya Care search engine.
Sources:
