Normative values of pulsatility index of fetal middle cerebral artery (MCA) at 12-41 weeks of gestation in a tertiary health facility in Jos, North Central, Nigeria.

Objective: The objectives of this study were to establish normative values of Foetal Middle Cerebral Artery Pulsatility index (MCA-PI) at 12-41 weeks of gestation for the Nigerian population and to compare values with Caucasians. Materials and Methods: Cross-sectional data were obtained from four hundred and eighty low-risk pregnant women from a tertiary health facility in Jos over fourteen months using real-time ultrasound and Doppler to establish reference values of the fetal middle cerebral artery (MCA) pulsatility index for fetal gestational ages between 12 and 41 weeks. Fetal biometrics and biophysical profile scores were measured using ultrasound to establish fetal gestational age and weight for subjects who met the inclusion criteria and were willing to participate in the study, while the fetal middle cerebral artery was scanned using Doppler to establish waveform values such as the peak systolic velocity and the end diastolic velocity, which were categorized into Pulsatility Index. Mean values of this index were used to construct percentile curves. Pearson’s correlation and regression curve were used to determine the relationship between fetal biometrics and Pulsatility Index. Z-test was used to compare mean values of subjects with Caucasian values. Results: Subjects consisted of 480 pregnant women between the ages of seventeen and forty years, with ages between 21- 30 years constituting 56.9% of the subjects. The findings of this study further showed that values of the middle cerebral artery pulsatility index rose gradually from 1.09±0.28 at 12 weeks, 1.22±0.22 at 24 weeks, and 0.90±0.20 at 36 weeks of gestation and then decreased towards the end of pregnancy. Pearson’s correlation of the pulsatility index with fetal gestational age showed a negative relationship, demonstrating a parabolic pattern in the regression curve (r=-0.421 at 0.01 level, 2-tailed). This relationship also yielded a regression curve equation as follows: pulsatility index =1.29GA -0.009. Conclusion: Our values showed that foetal middle cerebral artery pulsatility index rose gradually with advancing gestation, reaching a peak (1.22±0.22) at 24 weeks of gestation and then decreased towards the end of pregnancy. Pearson’s correlation of the pulsatility index with fetal gestational age showed a negative relationship, demonstrating a parabolic pattern in the regression curve (r=-0.421 at 0.01 level, 2-tailed). This relationship also yielded a regression curve equation as follows: pulsatility index =1.29GA -0.009, and there was a slight difference with Caucasian values. Though data distribution across variables, especially fetal gestational age, was uneven, findings from this study could serve as a useful guide to determine limits of normality in our environment.