Longitudinal assessment of the middle cerebral artery peak systolic velocity in healthy fetuses and in fetuses at risk for anemia.

Objective: Our purpose was to assess the feasibility of longitudinal assessment of the middle cerebral artery peak systolic velocity (MCA-PSV) to predict fetuses who will have severe anemia.
Study Design: Doppler measurement of MCA-PSV was serially performed in 15 healthy fetuses (99 measurements; range: 4-9 per fetus), 8 fetuses who were mildly anemic (41 measurements; range: 3-10 per fetus), and 11 who were severely anemic (50 measurements; range: 2-7 per fetus) at their first cordocenteses. Linear models were fitted to the data from individual fetuses and the slopes were determined. The average rate of change (slope) of MCA-PSV as a function of gestational age in the 3 groups was calculated from these data. Estimated average slopes were computed using restricted maximum likelihood. F tests were used for hypothesis tests, with the degrees of freedom based on the Kenward and Roger approximation. The values of MCA-PSV and hemoglobin were expressed as multiples of the median (MoM). A P <.05 indicated statistical significance.
Results: Gestational age at the time of the Doppler studies ranged from 15.1 to 41 weeks in the healthy fetuses. It was between 15 and 33.4 weeks in the fetuses who became anemic. The estimated average slopes increased with the degree of anemia (P =.03). The difference in mean slope between the severely anemic sample and the healthy sample was statistically significant (estimated difference = 2.2, SE =.65, P =.01). The difference in mean slope between the mildly anemic and healthy samples was not statistically significant (estimated difference = 1.1, SE =.06; P =.08).
Conclusions: We have demonstrated that the MCA-PSV slope is an excellent tool for identifying those fetuses who will become severely anemic and, therefore, need to be followed up more closely during the pregnancy. Our findings expand the clinical applications to which Doppler ultrasonography can be applied in monitoring pregnancies at risk for fetal anemia.