Abstract

Objective To assess clinical variability in the management of small‐for‐gestational‐age (SGA) fetuses according to different published Doppler reference charts for umbilical artery (UA) and fetal middle cerebral artery (MCA) Doppler indices and cerebroplacental ratio (CPR). Methods We performed a systematic search of MEDLINE, EMBASE, CINAHL and the Web of Science databases from 1954 to 2018 for studies with the sole aim of creating fetal Doppler reference values for UA, MCA and CPR. The top cited articles for each Doppler parameter were included. Variability in Doppler values at the following clinically relevant cut‐offs was assessed: UA‐pulsatility index (PI) > 95th percentile; MCA‐PI < 5th percentile; and CPR < 5th percentile. Variability was calculated for each week of gestation and expressed as the percentage difference between the highest and lowest Doppler value at the clinically relevant cut‐offs. Simulation analysis was performed in a cohort of SGA fetuses (n  = 617) to evaluate the impact of this variability on clinical management. Results From a total of 40 studies that met the inclusion criteria, 19 were analyzed (13 for UA‐PI, 10 for MCA‐PI and five for CPR). Wide discrepancies in reported Doppler reference values at clinically relevant cut‐offs were found. MCA‐PI showed the greatest variability, with differences of up to 51% in the 5th percentile value at term. Variability in the 95th percentile of UA‐PI and the 5th percentile of CPR at each gestational week ranged from 21% to 41% and 15% to 33%, respectively. As expected, on simulation analysis, these differences in Doppler cut‐off values were associated with significant variation in the clinical management of SGA fetuses, despite using the same protocol. Conclusions The choice of Doppler reference chart can result in significant variation in the clinical management of SGA fetuses, which may lead to suboptimal outcomes and inaccurate research conclusions. Therefore, an attempt to standardize fetal Doppler reference ranges is needed.