Changes in flow velocity, resistance indices, and cerebral perfusion pressure in the maternal middle cerebral artery distribution during normal pregnancy

Background. There are few longitudinal data currently available detailing t he normal changes in maternal cerebral hemodynamics during human pregnancy. This lack of information limits the study of pregnancy-associated cerebrov ascular adjustments and, in particular, preeclampsia, where the brain appea rs to be especially susceptible to ischemic and encephalopathic injury. Our objective was to define the hemodynamic changes, specifically velocity, re sistance indices, and cerebral perfusion pressure, in the middle cerebral a rtery (MCA) distribution of the brain during normal pregnancy. Methods and materials. Transcranial Doppler ultrasound was used to determin e the systolic, diastolic and mean blood velocities in the middle cerebral arteries in non-laboring women studied longitudinally during normal gestati on. The resistance index (RI), pulsatility index (PI), and cerebral perfusi on pressure (CPP) were calculated using the velocity and blood pressure dat a. Data were analyzed using a longitudinal statistical model incorporating random patient effects and a homoscedastic (compound symmetric) variance-co variance structure over time (gestational age). The predicted mean value (L east Squares Mean), and the 5th and 95th percentiles, were defined for norm al pregnancy. Results. MCA systolic velocity decreased (24%) as did the mean velocity(17% ). The diastolic velocity did not change significantly. The MCA RI decrease d by 19% and the PI decreased by 25%. The MCA CPP increased by 52% between 12 and 40 weeks of gestation. Conclusions. The normative ranges for MCA velocity, RI, and CPP have been d efined in normal human pregnancy using longitudinally collected data. By ha ving a defined normal range, identification of abnormalities in cerebral he modynamics during pregnancy is now possible, and this may help researchers and clinicians to elucidate etiologies and treatments for pregnancy-related pathophysiologic states such as preeclampsia.