Objectives: Our objectives were to determine the success rate in obtaining flow velocity waveforms in the first-trimester fetal circulation and to establish possible preferential flow to the fetal cerebrum at this early stage of gestation.
Study design: Flow velocity waveform recordings were made in the umbilical artery, fetal descending aorta, and fetal intracerebral arteries in 30 normal pregnancies between 11 and 13 weeks of gestation.
Results: Technically acceptable waveforms were obtained from the descending aorta in 15 fetuses, from the intracerebral circulation in 17 fetuses, and from the umbilical artery in all 30 fetuses. Absent end-diastolic velocities in the descending aorta and umbilical artery were associated with forward flow throughout the cardia cycle in intracerebral arteries.
Conclusion: A relatively low cerebral vascular resistance in the late-first-trimester normal fetus is suggested.