Can middle cerebral artery peak systolic velocity predict polycythemia in monochorionic–diamniotic twins? Evidence from a prospective cohort study

ABSTRACT Objective The antenatal diagnosis of twin anemia–polycythemia sequence ( TAPS ) in monochorionic–diamniotic ( MCDA ) twin pregnancies is based on elevated peak systolic velocity in the middle cerebral artery ( MCA‐PSV ) in the donor twin and decreased MCA‐PSV in the recipient twin. However, the association between these parameters and polycythemia has not yet been established. The aim of this study was to determine whether MCA‐PSV can predict polycythemia in MCDA pregnancies. Methods This was a prospective cohort study of MCDA pregnancies recruited at 14–18 weeks' gestation from a single tertiary care center between January 2011 and June 2014. Fetal MCA Doppler waveforms were recorded every 2 weeks from 18 weeks' gestation until delivery. Only those with an MCA‐PSV measurement within 1 week of delivery were included in the analysis. Neonatal hematocrit level was determined in all twins from venous blood obtained within 4 h of delivery. Polycythemia was defined as a hematocrit of > 65%, and anemia as a hematocrit of < 45%. TAPS was diagnosed when an intertwin hemoglobin difference of > 8 g/ dL and reticulocyte count ratio of > 1.7 were observed. Results Of 162 MCDA pregnancies followed during the study period, 69 had an MCA‐PSV measurement within 1 week of delivery and were included in the study. Twenty‐five neonates were diagnosed with polycythemia and nine twin pairs met the criteria for TAPS . In a pooled analysis, MCA‐PSV was negatively correlated with neonatal hematocrit ( P = 0.017, r = −0.215) and was significantly higher in anemic fetuses than in normal controls (1.15 multiples of the median ( MoM ) vs 1.02 MoM , respectively; P = 0.001). However, MCA‐PSV was similar among polycythemic and normal fetuses (0.95 MoM vs 1.02 MoM , respectively; P = 0.47). Intertwin difference in MCA‐PSV (delta MCA‐PSV ) was positively correlated with intertwin hematocrit difference ( P = 0.002, r = 0.394). Moreover, twin pregnancies with an intertwin hematocrit difference of > 24% had a significantly greater delta MCA‐PSV than did those with an intertwin hematocrit difference of ≤ 24% (delta MCA‐PSV , 19 vs 5 cm/s; P < 0.001). Conclusions MCA‐PSV is not significantly decreased in polycythemic MCDA twins. However, delta MCA‐PSV is associated with a large intertwin difference in hematocrit, and its use may be better than conventional methods for the risk assessment of TAPS . Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.