Twin anemia-polycythemia sequence (TAPS) is a chronic type of unbalanced fetal transfusion in monochorionic twins that results in polycythemia in the TAPS recipient and anemia in the TAPS donor due to tiny placental anastomoses.[1] Post-laser TAPS and spontaneous TAPS are the two forms of TAPS. Unlike twin-to-twin transfusion syndrome, which arises when twin oligohydramnios polyhydramnios sequence (TOPS) is present, TAPS develops in its absence.[2]
The cause of TAPS is slow and persistent unbalanced feto-fetal transfusion through tiny placental anastomoses, which progressively results in highly discordant hemoglobin levels. This causes the recipient twin to become polycythemic and the donor twin to become anemic.[1]
There are very few, tiny arteriovenous vascular anastomoses present in TAPS placentas. This distinct angiography is the foundation of the pathogenesis of TAPS. A slow transfusion of blood from the donor to the recipient is made possible by the few tiny anastomoses, which eventually cause very disparate hemoglobin levels. It's unclear if hormonal dysfunction may also contribute to the onset of TAPS.[6]
Doppler ultrasound abnormalities demonstrating an increased peak systolic velocity in the middle cerebral arteries (MCAPSV) in the donor twin and a decreased MCA-PSV in the recipient twin can be used to make an antenatal diagnosis of TAPS. The presence of polycythemia in the recipient and (chronic) anemia in the donor, along with characteristic placental angioarchitecture as determined by injection with colored dye, are the basis for the postnatal diagnosis of TAPS.[6]
The rate of residual anastomoses can be decreased to prevent postlaser TAPS. The "Solomon technique," an alternate method of laser surgery, may help lower the possibility of omitting a tiny anastomosis during the procedure.[6]
Weekly ultrasound monitoring, which includes a full staging Doppler examination with the MCA-PSV, is part of the expectant management protocol. The recent onset of ultrasound abnormalities may require an increase in the surveillance frequency. When TAPS patients present in the first or early second trimester, this approach is preferred because many of these patients may resolve or remain clinically stable. Expectant care can be continued with the aim of achieving a late preterm delivery in stable cases that do not advance past stage 2. It is necessary to take into account alternate management options if TAPS is accelerating.[7]
Postlaser TAPS can occur in 2–13% of cases, depending on the definitions and criteria applied.[10][11] The range of incidence for spontaneous TAPS is 3–5%.[6]
^Critically abnormal Doppler is defined as pulsatile flow in the umbilical vein, absent or reversed end-diastolic flow in the umbilical artery, increased pulsatility index, or reversed flow in the ductus veinosus.[6]
^Baschat, Ahmet A.; Miller, Jena L. (2022). "Pathophysiology, diagnosis, and management of twin anemia polycythemia sequence in monochorionic multiple gestations". Best Practice & Research Clinical Obstetrics & Gynaecology. 84. Elsevier BV: 115–126. doi:10.1016/j.bpobgyn.2022.03.012. ISSN1521-6934. PMID35450772. S2CID260972128.
^Herway, C.; Johnson, A.; Moise, K.; Moise, K. J. (2009). "Fetal intraperitoneal transfusion for iatrogenic twin anemia–polycythemia sequence after laser therapy". Ultrasound in Obstetrics & Gynecology. 33 (5): 592–594. doi:10.1002/uog.6334. ISSN0960-7692. PMID19402103.
