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.