What is Twin Anemia Polycythemia Sequence (TAPS)?
TAPS is a rare disease affecting 3-5% of twins who share a placenta. Where TTTS is caused by large connections in the placenta, and a sudden shift of blood from one twin to the other, in TAPS, it's a slow transfer of red blood cells from donor to recipient through tiny connections in the placenta. This causes one twin to have chronic anemia, and the other polycythemia. A great comparison is one twin having blood like rosé wine, and the other like ketchup.
TAPS is a rare disease affecting 3-5% of twins who share a placenta. Where TTTS is caused by large connections in the placenta, and a sudden shift of blood from one twin to the other, in TAPS, it's a slow transfer of red blood cells from donor to recipient through tiny connections in the placenta. This causes one twin to have chronic anemia, and the other polycythemia. A great comparison is one twin having blood like rosé wine, and the other like ketchup.
What's The Difference Between TTTS And TAPS?
Great question. There are several major differences between the two, but the most important one to remember is that there are no fluid differences in TAPS. In fact, there are no symptoms to the parent at all.
The most accurate way to diagnoses TAPS is using doppler ultrasound on the middle cerebral arteries of the babies. There are also other signs of TAPS, like a starry sky liver for recipients, and a "bright" or echogenic share of the placenta for donors, as well as an enlarged heart (cardiomegaly) for donors. But it's important to know that these "other signs" of TAPS are usually found when the disease is in advanced stages, and around 14% of cases will have no other sign other than discordant MCA-PSV readings.
What Are The Different Forms of TAPS?
There are two forms of TAPS. The first, and the oldest described form is post laser TAPS. This is the more rare form of TAPS, especially since the introduction of the Solomon Laser Technique.
This reduced the risk from 16% to just 0-3%. Post laser TAPS has similar long term outcomes to TTTS, but has a higher perinatal mortality rate (death just before, or just after birth) for donor twins at 26%.
Great question. There are several major differences between the two, but the most important one to remember is that there are no fluid differences in TAPS. In fact, there are no symptoms to the parent at all.
The most accurate way to diagnoses TAPS is using doppler ultrasound on the middle cerebral arteries of the babies. There are also other signs of TAPS, like a starry sky liver for recipients, and a "bright" or echogenic share of the placenta for donors, as well as an enlarged heart (cardiomegaly) for donors. But it's important to know that these "other signs" of TAPS are usually found when the disease is in advanced stages, and around 14% of cases will have no other sign other than discordant MCA-PSV readings.
What Are The Different Forms of TAPS?
There are two forms of TAPS. The first, and the oldest described form is post laser TAPS. This is the more rare form of TAPS, especially since the introduction of the Solomon Laser Technique.
This reduced the risk from 16% to just 0-3%. Post laser TAPS has similar long term outcomes to TTTS, but has a higher perinatal mortality rate (death just before, or just after birth) for donor twins at 26%.
The other form of TAPS happens spontaneously in 3-5% of monochorionic twins. It's more common (it's actually a myth that it's rarer than post laser TAPS - because post-laser TAPS happens in a small percentage of an already small percentage) Spontaneous TAPS can happen at any stage during the pregnancy with equal chance, unlike TTTS which is more common between weeks 16 and 24. The biggest difference though lies in the long term outcomes. In spontaneous TAPS, donor twins are at a high risk of neurodevelopmental impairment, and also at a 1 in 8 chance of being born profoundly deaf.
How Is TAPS Diagnosed?
There are 2 ways to get a TAPS Diagnosis – antenatally and postnatally. This article will explain both, and explain some important things you need to know about your TAPS diagnosis.
Before Birth: TAPS is most easily diagnosed using doppler ultrasound on the mid-cerebral artery, looking for fetal anemia. The most important thing to know is that the new Leiden Staging system is the most accurate way to diagnose TAPS stages before birth. TAPS staging looks like this:
TAPS Stage 1 >0.5 MoM difference in delta MCA-PSV
TAPS Stage 2 >0.7 MoM difference in delta MCA-PSV
TAPS Stage 3 Stage 1, or 2, but with cardiac compromise of the donor*
TAPS Stage 4 The donor develops hydrops **
TAPS Stage 5 One, or both babies die in utero
* cardiac compromise is defined as critically abnormal flow in either the umbilical artery or ductus venosus
** the baby develops pockets of fluid around critical organs
Doctors should also be aware of the other signs of TAPS on ultrasound, like cardiomegaly in donors, echogenic placental share for donors, and a “starry sky” liver for recipients. (Taken from the TAPS Support website here:)
After Birth: Postnatal TAPS is diagnosed via blood testing and placental pathology. Your babies will need their reticulocytes and hemoglobin tested, as well as their placenta sent for pathology to be checked for tiny connections between the babies. They will also calculate the difference in numbers between the babies, first subtracting the donor’s hemoglobin count from the recipients. They will also divide the donor’s reticulocyte count by the recipient’s, and calculate the ratio of these in the readings. The staging system looks like this:
TAPS Stage 1 Hemoglobin Difference >8.0g/dl
TAPS Stage 2 Hemoglobin Difference >11.0g/dl
TAPS Stage 3 Hemoglobin Difference >14.0g/dl
TAPS Stage 4 Hemoglobin Difference >17.0g/dl
TAPS Stage 5 Hemoglobin Difference >20.0g/dl
+ difference in reticulocyte ratio of 1:1.7
Before Birth: TAPS is most easily diagnosed using doppler ultrasound on the mid-cerebral artery, looking for fetal anemia. The most important thing to know is that the new Leiden Staging system is the most accurate way to diagnose TAPS stages before birth. TAPS staging looks like this:
TAPS Stage 1 >0.5 MoM difference in delta MCA-PSV
TAPS Stage 2 >0.7 MoM difference in delta MCA-PSV
TAPS Stage 3 Stage 1, or 2, but with cardiac compromise of the donor*
TAPS Stage 4 The donor develops hydrops **
TAPS Stage 5 One, or both babies die in utero
* cardiac compromise is defined as critically abnormal flow in either the umbilical artery or ductus venosus
** the baby develops pockets of fluid around critical organs
Doctors should also be aware of the other signs of TAPS on ultrasound, like cardiomegaly in donors, echogenic placental share for donors, and a “starry sky” liver for recipients. (Taken from the TAPS Support website here:)
After Birth: Postnatal TAPS is diagnosed via blood testing and placental pathology. Your babies will need their reticulocytes and hemoglobin tested, as well as their placenta sent for pathology to be checked for tiny connections between the babies. They will also calculate the difference in numbers between the babies, first subtracting the donor’s hemoglobin count from the recipients. They will also divide the donor’s reticulocyte count by the recipient’s, and calculate the ratio of these in the readings. The staging system looks like this:
TAPS Stage 1 Hemoglobin Difference >8.0g/dl
TAPS Stage 2 Hemoglobin Difference >11.0g/dl
TAPS Stage 3 Hemoglobin Difference >14.0g/dl
TAPS Stage 4 Hemoglobin Difference >17.0g/dl
TAPS Stage 5 Hemoglobin Difference >20.0g/dl
+ difference in reticulocyte ratio of 1:1.7
How Is TAPS Treated?
Right now, TAPS can be treated in several different ways. Laser surgery using the Solomon Technique, Expectant Management (or Watch and Wait), in utero blood transfusions, early delivery once the babies reach viability, or in extreme cases, where one baby is too ill to survive, selective reduction. This is a difficult decision for families to make, and it's important to treat them with compassion and kindness.
We still don't know the best treatment for TAPS, so most health care providers advocate for an individualized approach, depending on the stage, the severity, the gestation, and of course, the parent's wishes. You can learn more about the international clinical trial that is investigating TAPS treatments, The TAPS Trial, on their website here.
We still don't know the best treatment for TAPS, so most health care providers advocate for an individualized approach, depending on the stage, the severity, the gestation, and of course, the parent's wishes. You can learn more about the international clinical trial that is investigating TAPS treatments, The TAPS Trial, on their website here.
Is TAPS A Form of TTTS?
No. Both are separate, distinct diseases with different ORPHAnet classifications (rare disease listings). They have their own unique diagnostic criteria, pathogenesis, long-term outcomes, and treatments. They are both diseases of the placenta, but can happen individually or at the same time. You can read more about the differences here.
Long-Term Outcomes of TAPS
Post-Laser TAPS.
There are a lot of similarities between the long term effects of post-laser TAPS, and TTTS. They are very different from spontaneous TAPS, with no difference between donors and recipients. There is around a 9% chance of neurodevelopmental impairment, with a 17% incidence of mild, to moderate, cognitive delays. Read more on our TTTS Page.
Spontaneous TAPS.
Donor twins are at four times higher risk of neurodevelopmental impairment than recipient twins, with 18% having a diagnosis of severe NDI. 26% of donor twins had a moderate to mild NDI diagnosis.
Bilateral deafness was observed in 1 in 8 donor twins as well.
The neurodevelopmental impairment seemed to be associated with severe fetal anemia, fetal growth restriction, and low gestational age at birth. In fact, donors with severe fetal anemia were 6 times more likely to have NDI.
Behavioral problems were also reported in 10% of the total group. Read more, and watch videos from the TAPS Support Team on their website here.
Supporting Research
Spontaneous TAPS: High risk of long-term neurodevelopmental impairment in donor twins with spontaneous twin anemia–polycythemia sequence – Tollenaar et al, 2020
Post-Laser TAPS: Neurodevelopmental outcome in twin anemia polycythemia sequence after laser surgery for twin–twin transfusion syndrome – Slaghekke et al, 2014
There are a lot of similarities between the long term effects of post-laser TAPS, and TTTS. They are very different from spontaneous TAPS, with no difference between donors and recipients. There is around a 9% chance of neurodevelopmental impairment, with a 17% incidence of mild, to moderate, cognitive delays. Read more on our TTTS Page.
Spontaneous TAPS.
Donor twins are at four times higher risk of neurodevelopmental impairment than recipient twins, with 18% having a diagnosis of severe NDI. 26% of donor twins had a moderate to mild NDI diagnosis.
Bilateral deafness was observed in 1 in 8 donor twins as well.
The neurodevelopmental impairment seemed to be associated with severe fetal anemia, fetal growth restriction, and low gestational age at birth. In fact, donors with severe fetal anemia were 6 times more likely to have NDI.
Behavioral problems were also reported in 10% of the total group. Read more, and watch videos from the TAPS Support Team on their website here.
Supporting Research
Spontaneous TAPS: High risk of long-term neurodevelopmental impairment in donor twins with spontaneous twin anemia–polycythemia sequence – Tollenaar et al, 2020
Post-Laser TAPS: Neurodevelopmental outcome in twin anemia polycythemia sequence after laser surgery for twin–twin transfusion syndrome – Slaghekke et al, 2014
More Information and Support
TAPS Support
Fetal Health Foundation
Twins Trust - TAPS
NORD - Twin Anemia Polycythemia Sequence
Support Groups
TAPS Support Facebook Group
International Clinical Trials
The TAPS Trial - Leiden University Medical Center
TAPS Registry (closed)
The Solomon Study (closed)
Fetal Health Foundation
Twins Trust - TAPS
NORD - Twin Anemia Polycythemia Sequence
Support Groups
TAPS Support Facebook Group
International Clinical Trials
The TAPS Trial - Leiden University Medical Center
TAPS Registry (closed)
The Solomon Study (closed)
