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

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.