Can we improve on the ultrasound diagnosis of fetal growth restriction?

Abstract

In spite of the widespread use of ultrasound techniques in screening for fetal growth restriction (FGR), field studies have failed to demonstrate any improvements in clinical outcome. This may be due either to the fact that ultrasound techniques in use are flawed or the clinical management of detected FGR cases is ineffective. Most ultrasound units attempt to detect FGR by serial plotting of the fetal ultrasound parameters, particularly of the fetal abdominal circumference (FAC). Field studies have shown that estimated fetal weight (EFW) is clinically more effective to perform this task than FAC alone. We got confirmation that this is the case by using computer simulation methods. Using FAC alone, serial measurements should not be taken more often than once every three weeks, as high false positive rates may otherwise ensue. On the other hand EFW can be measured more often with a lower false positive rate. Ultrasound formulae for assessing fetal weight are subject to considerable error. Much of this error is related to the characteristics of the formula itself. Our study with computer modeling techniques has shown that there is a general trend to overestimate fetal weight at term and to underestimate it in the preterm period. This trend can be minimized by using volumetric formulae instead of exponential formulae. Most units use reference standards that are not adjusted for maternal characteristics. The use of such unadjusted charts often leads to higher false positive rates and consequently to inappropriate intervention. Computer software is now available to generate individually customized fetal growth standards for EFW.