Middle Cerebral and Umbilical Doppler Norms Based on Sonographic Fetal Measurements During the Third Trimester

Abstract

Fetal umbilical artery (UA) and middle cerebral artery (MCA) doppler resistance indices may be useful in the management of intrauterine growth retardation and other conditions leading to fetal compromise. Their interpretation is dependent on gestational age, however. When fetal compromise is suspected and gestational age is not certain, norms based on fetal size or independent of age would be useful. This study developed norms for UA and MCA resistance indices (RI) based on fetal biparietal diameter (BPD) and femur length (FL) measurements performed within one week of doppler interrogation during the third trimester from 70 studies performed on 48 women who had suspicion of fetal compromise and questionable dating, but normal pregnancy outcome. UA RI was significantly related to BPD: UA RI = 1.107 − 0.0585 × BPD (cm) ± 0.053 RMSE (R² = 0.251, P < 0.0001). MCA RI was related to FL: MCA RI = 1.121 - 0.045 × FL (cm) ± 0.033 RMSE (R² = 0.369, P < 0.0001). Additionally, the difference between them (MCA RI – UA RI = DRI) was unrelated to gestational age, simple to calculate, and had percentiles: minimum = 0.04, 5th percentile = 0.09, 10th percentile = 0.115, 25th percentile = 0.165, 50th percentile = 0.220, proposed threshold 0.10. These doppler profile norms may be useful for the management of suspected pregnancy complications when gestational age is uncertain.

Key Words:

• Blood flow velocity
• Umbilical artery
• Middle cerebral artery
• Fetus
• Ultrasound measurements
• Normal values