A new study published in the January issue of the Journal of Ultrasound in Medicine has shown that a 3D Doppler ultrasound can more accurately determine altered fetal growth restriction (FGR) in fetuses vulnerable to developing abnormal cerebral vascular flow patterns than a standard 2D Doppler ultrasound.
According to the study's lead author Katherine R. Goetzinger, MD, MSCI, of University of Maryland's School of Medicine, the findings may help to more accurately determine in pregnant women the difference between pathologic FGR and "constitutionally small growth" of the fetus.
"The current clinical standard used to assess the fetal brain circulation is 2D pulsed Doppler evaluation of the middle cerebral artery," Goetzinger said. "This approach has both technical limitations and practical concerns, including its inability to accurately detect subtle changes in blood flow in small vessels and its assumption that redistribution of blood flow to all regions of the brain is symmetric."
FGR affects four to eight percent of pregnancies, according to the study, leading to fetal morbidity and mortality in fetuses that have an ultrasound-estimated weight below the 10th percentile.
"With the advent of 3D-power Doppler techniques, it has been possible to actually quantify blood flow in fetal organs, including the kidney, liver, and placenta, by assessing both vascularization and flow indices," Goetzinger said.
This prospective cohort study recruited women between 24 and 36 weeks' gestation with clinically identified FGR and were matched with a control with appropriate gestational age (AGA) fetuses from Washington University between 2011 and 2013. In total, 306 female patients qualified for the study and were given a standardized 3D Doppler ultrasound of the middle cerebral artery territory in the fetus by qualified obstetric sonographers. Researchers measured the vascularization index (VI), flow index (FI), and vascularization-flow index (VFI) were calculated by the Virtual Organ computer-aided analysis technique, according to study methods. Additionally, a follow-up study was performed on 20 patients selected randomly in the cohort to ensure reality and accuracy of the measurements.
Of the 306 patients, 151 cases were indicated as FGR. According to study findings, FI was higher in FGR fetuses compared to AGA controls, along with a significantly negative correlation between the FI, middle cerebral artery pulsatility index and cerebroplacental ratio. FGR fetuses were also significantly younger, had a lower BMI and were delivered earlier with a lower birth weight than AGA fetuses.
"The novel application of this technique in the assessment of FGR may have the potential to identify fetuses with brain-sparing pathophysiologic states earlier in the course of gestation, which could have implications for fetal surveillance strategies and the timing of delivery," concluded Goetzinger.
The advantages of a 3D power Doppler ultrasound over a 2D pulsed Doppler ultrasound are significant in that this study was able to evaluate an entire region of perfusion, as opposed to a singular vessel, explained Goetzinger. Its intricate detection of low-velocity blood flow and its independence of requiring a particular angle of insonation were also strengths of the study.
However, Goetzinger and colleagues cited a few study limitations, including a lack of serial ultrasound data, the inability to analyze rare neonatal outcomes and short term and long term neurodevelopmental dysfunction and a small study population.