Evaluation of pulsatility index nomograms based on fetal biometry in small for gestational age fetuses

Reference limits for the PI from the umbilical, middle cerebral, and renal arteries were constructed using BPD, AC, FL, and transverse cerebellar diameter as independent variables and their efficacy tested in a population of SGA fetuses. Therefore, 153 normal fetuses and 90 SGA fetuses with established dates between 20 and 40 weeks of gestation were considered. Normal fetuses showed a linear negative relationship between the PI from all the vessels investigated and all the biometric parameters considered. Although the BPD related better with the PI from the umbilical artery (r = 0.646) and the renal artery (r = 0.765) and the transverse cerebellar diameter related better with middle cerebral artery PI values (r = 0.510), no evident differences in fitting were found among the variables tested. In SGA fetuses the nomograms on BPD, AC, and FL significantly underestimated PI values in all the vessels studied when compared to the nomograms based on gestational age, while a similar ability in identifying abnormal PI values was found for nomograms based on gestational age and transverse cerebellar diameter. These newly developed nomograms based on transverse cerebellar diameter may prove useful in the evaluation of Doppler indices of fetuses with uncertain gestational age.