[Normal reference values of the pulsatility index and peak systolic velocity in the fetal middle cerebral artery during normal pregnancy].

OBJECTIVE

To establish the normal reference values of the fetal middle cerebral artery (MCA) pulsatility index (PI) and MCA peak systolic velocity (PSV) during normal pregnancy.

PARTICIPANTS AND METHODS

A total of 727 normally grown fetuses were evaluated with pulsed Doppler ultrasound between 20 and 40 weeks of gestation. The MCA was located in a transverse view of the fetal head 1 cm after its origin from the Willis vascular circle. The insonation angle was always kept as close as possible to 0. The PI and PSV were measured in 5 consecutive and uniform cardiac cycles and the mean considered as the representative for each case. Normal reference values for each gestational week were constructed. Reproducibility and agreement were analyzed for the MCA PI estimation.

RESULTS

There was a significant correlation between MCA PSV and gestational age (GA) (PSV = -13.81+1.96 X GA, r2 = 0.59, p=0.001). The correlation between MCA PI and GA showed an initial increment until week 30 with a further reduction towards the end of the pregnancy (MCA PI = 2.44 + -0.02 X EG, r2 = 0.09). Reproducibility analysis of the MCA PI estimation showed an intra-class and inter-class correlation coefficients of 0.89 (95%CI 0.65-0.97) and 0.87 (95% CI 0.63-0.93), respectively. Agreement evaluation showed a mean difference between observers of 0.03 (standard deviation 0.19), with 95% limits of agreement of -0.41 a 0.35.

CONCLUSION

The normal reference values obtained in this study confirm the diagnostic and prognostic capacity of the fetal MCA PI and the MCA PSV evaluation in high risk pregnancies.