PURPOSE: to study the evolution of the resistance and pulsatility indices, maximum velocity, final diastolic velocity and time of acceleration of the middle cerebral artery of fetuses between 22 and 38 weeks of gestation. METHODS: a prospective and longitudinal observational study was conducted on 33 fetuses of normal pregnant women evaluated between 22 and 38 weeks of pregnancy. The gestational age was determined on the basis of the date of the last menstruation and/or by ultrasound examination during the first trimester. Doppler ultrasound examination was performed by a single observer using an Image Point 1800 (Hewlett Packard) apparatus equipped with a multiple frequency transducer. For the acquisition of the Doppler tracing of the middle cerebral artery, the sample indicator was calibrated for a sample volume of 1 mm³ and placed on the anterior middle cerebral artery as close as possible to the skullcap. The insonation angle was kept between 5º and 19º and the filter was adjusted to a frequency of 50-100 Hz. The newborn infants were evaluated in order to confirm that the fetuses were vigorous and adequate for gestational age. RESULTS: the results obtained for the resistance and pulsatility indices revealed a 2nd-degree equation, representing a parabola whose values for the resistance index were 0.81 during the 22nd week and 0.75 during the 38th week. The pulsatility index was 1.59 during the 22nd week and 1.45 during the 38th week. Maximum systolic velocity increased progressively along pregnancy, with values of 26.3 cm/s during the 22nd week and 57.7 cm/s during the 38th week. Final diastolic velocity increased progressively from the 26th week (5.21 cm/s) to term (14.6 cm/s). Acceleration time increased significantly only between 26 and 30 weeks, with values of 0.04 s during the 26th week and 0.05 s during the 30th week. CONCLUSION: it was concluded that the evolution of the resistance and pulsatility indices and of maximum systolic velocity were similar to those of most studies described in the literature. Acceleration time presented few modifications during the evaluated gestational weeks.
Middle cerebral artery; Ultrasonography; Doppler velocimetry; Normal pregnancy
