OBJECTIVETo summarize and review the clinical characteristics including clinical features, prenatal characteristics, diagnosis, treatments and short-term outcomes of the twin anemia-polycythemia sequence (TAPS) to improve the recognition of the disease.

METHODThe clinical data of one case with twin anemia-polycythemia sequence and the reports of 15 cases seen in the past 5 years were reviewed and analyzed.

RESULTThere was an increasing number of reports of cases with TAPS. Prenatal manifestation: among the 16 cases, TAPS occurred in 13 cases naturally and in 3 cases occurred after laser treatment. Amniotic fluid volume showed no significant difference in 16 cases. Middle cerebral artery peak systolic velocity (MCA-PSV) > 1.5 multiples of the median (MoM) in the donor were 11/16 cases and 3/16 cases were not tested. MCA-PSV < 1.0 MoM in the recipient were seen in 10/16 cases and in 3/16 cases MCA-PSV was not tested. Hydrops fetalis was found in 6/16 cases. Intrauterine intervention: intrauterine blood transfusion was performed in 4/16 cases, fetoscopic laser occlusion of chorioangiopagus vessels was performed in 4/16 cases, umbilical cord occlusion selective feticide was done in 2/16 cases and intrauterine hemodilution in the recipient was performed in 1/16 case. Postnatal manifestation: average hemoglobin concentration in the anemic neonate was 95 g/L and in the polycythemic one was 208 g/L, intertwin Hb difference was > 80 g/L in 10/16 cases and < 80 g/L in 2/16 cases (after intrauterine laser treatment). Intertwin reticulocyte count ratio was > 1.7 in 5/16 cases and < 1.7 in 1/16 case (after intrauterine laser treatment). Postnatal treatment: 9/16 cases of donor had anemia, among them, 6/16 cases were given blood transfusions, 6/16 cases of recipient with hyperviscosity underwent partial exchange transfusions. Neurodevelopmental follow-up during neonatal period was normal in 11/16 cases, in our case, neurodevelopmental follow-up at the corrected gestational age 3 months was normal.

CONCLUSIONTAPS is a new atypical form of twin-twin transfusion syndrome (TTTS) that presents as a large intertwin hemoglobin difference with one twin developing anemia and the other developing polycythemia, without oligohydramnios-polyhydramnios sequence that is required for the diagnosis of TTTS. We suggest that routine doppler studies and MCA-PSV measurements should be performed during each follow-up visit in all uncomplicated monochorionic twin pregnancies, in order to find out the cases required intrauterine intervention to decrease neonatal mortality rates and improve the prognosis.