Acceleration time in the fetal middle cerebral artery during the second half of pregnancy.

We made a longitudinal ultrasonographic study of 33 healthy fetuses from 22 to 38 weeks of gestation to determine the acceleration time in the middle cerebral artery (ATMCA) and its relationship with fetal cardiac output. Doppler ultrasound (US) was performed by a single observer always using the same apparatus. The Doppler tracing was obtained with a sample volume of 1 mm; placement was on the anterior middle cerebral artery, as close as possible to the skullcap. The insonation angle was kept between 5 degrees and 19 degrees and the wall filter was adjusted to a frequency of 50 to 100 Hz. The ATMCA was 40 ms at 22 and 26 weeks, 50 ms at 30 and 34 weeks and 60 ms at the 38th week. There was a significant positive correlation between gestational age and ATMCA values (r=0.45, p<0.001). The ATMCA values became significantly higher than the initial values at the 30th week of gestation (p<0.05). The ATMCA values for normal fetuses could be compared with those obtained during high-risk pregnancies; this would be useful for the detection of fetal cardiac anomalies.