Abstract
With respect to the assessment of fetal behaviour, there have been numerous reports on the conventional twoโdimensional (2โD) ultrasonographic evaluation of fetal movements. However, there are some limitations regarding the assessment of fetal movements using 2โD ultrasound. Because of the 2โD character of realโtime scanning, fetal movements outside the scanning plane cannot be displayed on the monitor. The advent of threeโdimensional (3โD) ultrasound significantly advanced fetal and placental evaluation in normal and abnormal pregnancies. The introduction of fourโdimensional (4โD) ultrasound techniques would allow the assessment of fetal behavioural assessment in three dimensions in real time during pregnancy. We present the latest 4โD sonographic techniques and recent 4โD sonographic studies on fetal behaviour, especially fetal wholeโbody movements and facial expressions in all three trimesters of pregnancy, and the continuation of behaviour from the fetal to neonatal period. 2โD does not appear capable or comparable to 4โD ultrasound in terms of evaluating early fetal facial expressions. Moreover, we describe the safety of 3โD/4โD ultrasound during pregnancy. This novel technique may assist in the evaluation of fetal behaviour, and offer potential advantages relative to conventional 2โD ultrasound. 4โD ultrasound may be an important modality in future research on fetal neurobehavioural development, although some limitations regarding the assessment of fetal behaviour by means of 4โD ultrasonography still remain unresolved. Copyright ยฉ 2009 John Wiley & Sons, Ltd.