Introduction
Twin anemia-polycythemia sequence (TAPS) is a rare condition that is seen in monochorionic pregnancies. It occurs as a result of unequal sharing of red blood cells between twins. This condition is a form of twin-to-twin transfusion syndrome that complicates twin pregnancies. Twin anemia-polycythemia sequence occurs randomly or after an incomplete laser surgery that was performed to treat twin-to-twin transfusion syndrome (TTS).
What Is Twin Anemia Polycythemia Sequence (TAPS)?
Twin anemia-polycythemia sequence is a condition that affects monochorionic pregnancies. Monochorionic pregnancy refers to a pregnancy with multiple fetuses (babies), such as twins or triplets. In a twin or triplet pregnancy, placentation can be dichorionic or monochorionic. Each fetus has a separate placenta in dichorionic placentation, whereas, in monochorionic placentation, both fetuses share a common placenta. In monochorionic pregnancies, complications like twin-to-twin transfusion syndrome are usually seen. Twin-to-twin transfusion syndrome is a condition in which the blood supply between the fetuses is disproportionate, resulting in unequal amounts of amniotic fluid between each fetus. If this condition is left untreated, the unsupplied twin dies, and the surviving twin may have morphological abnormalities.
Twin anemia-polycythemia sequence is a type of twin-to-twin transfusion syndrome. However, it is significantly different from twin-to-twin transfusion syndrome. In the twin anemia-polycythemia sequence, there is an unequal sharing of red blood cells between the fetuses sharing a single placenta. As a result, an imbalance in hemoglobin and red blood cells occurs. Hence, one twin does not receive an adequate supply of oxygen and nutrients required for development. This unequal distribution of red blood cells between the monochorionic twins results in anemia (a condition in which the number of red blood cells is reduced) in one twin and polycythemia (a condition in which an increased number of red blood cells are present in the blood) in the other twin, causing twin anemia-polycythemia sequence.
What Causes TAPS?
TAPS is the after-effect of a lopsidedness of remote connections in the outer layer of the placenta that permit red blood cells to be moved from one baby to the other. The embryo sending blood to its co-twin winds up with a lesser number of red blood cells (iron deficient), while the one getting the blood has too many red blood cells (polycythemia). The condition can occur as a result of monochorionic pregnancy or after fetoscopic laser surgery (a procedure that stops the abnormal fluid exchange between twins). This procedure is used to treat TTTS (twin-to-twin transfusion syndrome). TAPS can occur as a reaction to this form of laser surgery.
How Does Twin Anemia-Polycythemia Sequence Occur?
Most of the monochorionic diamniotic (amniotic fluid) placentas are characterized by intertwined anastomoses (connections) that are either bidirectional artery-to-artery anastomosis, unidirectional artery-to-vein anastomosis, or vein-to-vein anastomosis. This presence of artery-to-vein anastomosis causes unequal sharing. This unidirectional blood flow compensates for the vascular flow to one twin. This contributes to the development of twin-to-twin transfusion syndrome (TTTS). The difference in TAPS is that the twin with the compromised supply (anemic twin) responds with a compensatory release of erythropoietin (a hormone that stimulates the production of red blood cells). However, the polycythemic twin may suppress the production of erythropoietin, resulting in reticulocytosis (an increase in immature red blood cells) in the anemic twin. Reticulocytosis in anemic twins is a classic sign that helps distinguish TAPS from TTTS.
What Are the Risks of Twin Anemia Polycythemia Sequence?
The following may be the risks of twin anemia polycythemia sequence:
-
Any history of laser surgery before pregnancy.
-
In the case of pregnancy that is monochorionic, that is, multiple pregnancies such as twins and triplets.
What Are the Symptoms of TAPS?
-
In TAPS, due to the lack of balance in the blood flow between the twins, the beneficiary twin gets excessive red blood cells and is at greater risk of sluggish blood flow, otherwise called polycythemia. This can lead to the formation of blood clumps, known as thrombosis. The other twin has a deficiency of red blood cells and is at a greater risk of developing hydrops (fluid builds up in the baby’s tissues and organs, resulting in extensive swelling) and anemia.
-
Unlike TTTS, the mothers carrying twins with TAPS do not encounter any symptoms at all. This condition is known to develop gradually over one’s pregnancy. Unlike TTTS, in TAPS, there is no alteration to the amniotic fluid levels.
-
Now and again, the twin's placenta, which receives more blood, might seem thickened.
-
The liver may develop bright white spots, also known as starry sky liver.
How Are TAPS Evaluated and Diagnosed?
The most pivotal move toward assessing a twin pregnancy for twin anemia polycythemia sequence is to decide if the twins share a solitary placenta. An ultrasound assessment from the get-go in pregnancy (during the primary trimester) can best make this qualification. Twin anemia polycythemia sequence can likewise affect the cardiovascular arrangement of one or the other twin. It is essential to perform a cardiovascular evaluation of the twins during pregnancy to rule out any other complications. The evaluation will involve the following examinations:
-
Ultrasound - An ultrasound examination is performed to rule out morphological abnormalities in twins. It also helps detect the placental location and umbilical cord insertion into the placenta, amniotic fluid levels, and blood flow patterns for each twin.
-
The Thickness of Blood - The thickness of blood depends on the blood the twin receives. The more blood, the slower the blood flow, and vice-versa.
-
Fetal Echocardiogram - An engaged ultrasound of each twin's heart to look for any heart conditions. TAPS might cause serious cardiovascular strain in the affected twin. This could lead to various heart conditions, such as cardiomegaly (enlarged heart) and various dysfunction of the heart. All twins assessed for TAPS ought to go through a fetal echocardiogram.
-
Amniocentesis - A method wherein a small quantity of amniotic liquid is obtained from the sacs encompassing the twins and evaluated for abnormalities. This test is used as a conjunct to other diagnostic and imaging tests to arrive at a diagnosis. Since TAPS grows gradually and can advance undetected, week after week, MCA Doppler studies are suggested in monochorionic pregnancies, starting somewhere in the range of 16 and 18 weeks.
-
Middle Cerebral Arterial Doppler Study - It is a type of ultrasound that is used to measure the blood flow through a blood vessel in the fetal brain. It also helps in detecting the difference in the speed of blood flow between the twins, if present. The blood will move faster than normal in the donor twin due to the presence of anemia as the blood is thinner, and the blood will move slower in the recipient twin due to the presence of polycythemia, in which the blood is thicker.
After birth, TAPS can be diagnosed by testing the twins' red blood cell count and analyzing the placenta to determine blood vessel connections.
How Is This Condition Treated?
Treatment for twin anemia polycythemia sequence may include the following:
-
Early Management - In circumstances where the medical procedure is not yet demonstrated, close observation with periodic Doppler ultrasound assessments is utilized to assess the state of the two twins and search for indications of movement. At times, a subsequent fetal echocardiogram is utilized, too, to search for indications of cardiovascular changes; these may, in some cases, be seen before different changes.
-
Fetal Selective Laser Ablation - It is a minimally invasive surgical procedure that is performed on the placenta to disconnect the blood vessels that communicate. This procedure stops the sharing of blood between twins and prevents the progression of the transfusion of blood cells. This strategy is additionally called specific laser photocoagulation (SLPC).
-
Intrauterine Blood Transfusion - In certain cases, laser medical procedures are, as of now, not conceivable because of late gestational age and intrauterine bonding for the weak baby. In these cases, diluting or thinning of the blood to the polycythemic baby can be considered.
-
Preterm Delivery - When TAPS happens towards the end of gestation, the ideal choice of treatment is to opt for an early delivery to prevent any further complications.
What Are the Follow-up Care For TAPS?
The doctor provides a point-by-point postoperative consideration and guidelines if one undergoes fetal mediation. The doctor plans for an ultrasound at appropriate intervals to look for the wellness of the mother and the children. After that test, the doctor prescribes or refers the patient to a maternal-fetal medication expert for somewhere around three weeks of week-after-week ultrasound assessments. The entire process will be taken care of using a multidisciplinary approach.
Conclusion:
TAPS is a condition in which the twins are affected by unequal blood flow. One twin gets more blood than the other, and the blood flow may be thicker in one twin compared to the other. This can affect the development of both twins. The symptoms are not felt until late gestation. However, this condition can be diagnosed in a routine ultrasound and managed appropriately. The treatment depends on the stage of the condition and the pregnancy.
