Middle Cerebral Artery Blood Flow Velocity During Normal Pregnancy

The present study aimed to evaluate resting middle cerebral artery (MCA) blood flow velocities using transcranial Doppler ultrasound (TCD) in healthy women at different stages of pregnancy, and to compare these velocities with those of normal controls.

A total of 105 healthy normotensive pregnant women and 25 non-pregnant healthy controls were included in the study. We formed 3 groups according to gestational age: first trimester (7 to 13 wk pregnant), second trimester (14 to 28 wk pregnant), and third trimester (29 to 42 wk pregnant). Age, body mass index, heart rate, arterial blood pressure, and hematological data were recorded and TCD was performed on the subjects. Regarding TCD, we evaluated the mean cerebral blood flow velocity, the peak systolic velocity, the end-diastolic flow velocity, S/D ratio, the pulsatility Index (PI) and the resistance Index (RI).

The MCA mean blood flow velocities differed significantly among the groups ( P <0.001) and were higher in the controls than those of the first trimester, second trimester, and third trimester groups ( P <0.01, P <0.001, P <0.001 respectively). The MCA mean and peak blood flow velocities, and the PI and RI decreased significantly with advancing gestation.

TCD is a noninvasive and non-toxic method of monitoring the adaptation of the maternal cerebral blood flow in pregnancy. The progressive decreases in the MCA mean and peak blood flow velocities, PI, and RI during gestation may be the result of chemical and neuronal factors. This study supports the need for additional studies using TCD to establish normative cerebral blood flow volumes throughout pregnancy.