The diagnosis can be reached either antenatally or postnatally. Antenatal diagnosis of TAPS is based on Doppler ultrasound abnormalities showing an increased middle cerebral artery peak systolic velocity (MCA-PSV) in the donor twin, suggestive of fetal anemia (>1.5 MoM), and a decreased MCA-PSV in the recipient twin, suggestive of polycythemia (<1.0 MoM), in the absence of signs of TOPS1.
Additional ultrasound findings can be a difference in placenta thickness and echodensity. A hydropic placenta part of the anemic twin and a normal placental part of the recipient twin1. Or a starry sky aspect of the liver in the recipient twin suspect for polycythemia2.
Antenal staging system1
|Stage 1||MCA-PSV > 1.5MoM in the donor and MCA-PSV <1.0MoM in the recipient|
|Stage 2||MCA-PSV > 1.7MoM in the donor and MCA-PSV <0.8MoM in the recipient|
|Stage 3||As stage 1 or 2, with cardiac compromise*|
|Stage 4||Hydrops of donor|
|Stage 5||Intrauterine fetal demise of one or both fetuses|
*Cardiac compromise is defined as critically abnormal Doppler findings: absent or reversed end-diastolic flow in umbilical artery, pulsatile flow in umbilical vein, increased pulsatility index or reversed flow in ductus venosus.
Postnatal diagnosis is based on inter-twin Hb difference ≥ 8.0 g/dL and at least one of the following criteria: reticulocyte count ratio ≥ 1.7 and/or small anastomoses (< 1 mm) at the placental surface3.These additional criteria are to distinquish between the acute form of transfusion through large anastomoses as seen in acute peripartum TTTS and the chronic form of transfusion as seen in TAPS.
Postnatal staging system1
|Stage||Hb difference (g/dL)|
|Stage 1||> 8.0|
|Stage 2||> 11.0|
|Stage 3||> 14.0|
|Stage 4||> 17.0|
|Stage 5||> 20.0|
Post-laserTAPS placenta after color dye injection4 showing the characteristic difference in color between the two placenta shares and the typical few tiny anastomoses. Blue and green dye was used to stain the arteries, and pink and yellow dye was used to stain the veins. The small arrows show the transfusion direction of the tiny anastomoses.
(1) Slaghekke F, Kist WJ, Oepkes D, Pasman SA, Middeldorp JM, Klumper FJ et al. Twin anemia-polycythemia sequence: diagnostic criteria, classification, perinatal management and outcome. Fetal Diagn Ther 2010; 27(4):181-190.
(2) Soundararajan LP, Howe D. Starry sky liver in twin anemia polycythemia sequence. Ultrasound Obstet Gynecol 2013. doi: 10.1002/uog.13276.
(3) Lopriore E, Slaghekke F, Oepkes D, Middeldorp JM, Vandenbussche FP, Walther FJ. Hematological characteristics in neonates with twin anemia-polycythemia sequence (TAPS). Prenetal Diagnosis 2010; 30(3):251-255.
(4) Lopriore E, Slaghekke F, Middeldorp JM, Klumper FJ, van Lith JM, Walther FJ et al. Accurate and simple evaluation of vascular anastomoses in monochorionic placenta using colored dye. J Vis Exp 2011;(55):e3208.