Objective: To establish the reference ranges of the middle cerebral artery pulsatility index ( MCA PI ) in normal fetuses between 20 and 37 weeks gestation.
Study design: A descriptive study.
Setting: Antenatal Care Clinic, Outpatient department, Faculty of Medicine, Srinagarind Hospital, Khon Kaen University.
Subjects: At least sixteen women of each gestational age with an uncomplicated singleton pregnancy between 20 and 37 weeks gestation.
Method: All recruited pregnant women were enrolled for abdominal Doppler ultrasonography to determine fetal MCA PI for each week of gestational age.
Main outcome measures: The MCA PI reference range for normal fetuses between 20 and 37 completed weeks of gestation.
Results: The MCA PI decreased as gestational age advanced from 1.97 (SD 0.48) at 20 weeks to 1.15 (SD 0.18) at 37 weeks.
Conclusion: We established the reference ranges of the fetal MCA PI for reference use in our Antenatal Care Clinic.

Keywords: Pulsatility index, Middle cerebral artery, Doppler ultrasound