Ultrasound (US) has been the modality of choice for assessment of the development of the embryo and fetus in the womb. Threedimensional US has made the study of the fetal anatomy even more accurate and understandable. But fetal development is not only the development of the structures but also their functionality. The functionality of the kidneys, e.g., can be confirmed by urine production and filling of the bladder, the functionality of the bladder by its periodically emptying and filling, and that of the heart by fetal circulation. The function of the nervous system is the most complex and this can be studied by fetal movements and fetal expressions. The development of fetal motor behaviors can be studied by real-time US.¹ The fetal activity observed or recorded with US equipment is fetal behavior.² Study of the fetal movements has been found to be more correlating with the fetal central nervous system (CNS) development. Studies have shown that the development and maturation of the fetal nervous system is reflected by quality and quantity of fetal movements.^3,4 On comparing the fetal movements with morphological studies, it was found that the fetal behavioral patterns directly reflected the development and maturation of fetal CNS. Therefore, assessment of fetal behavior in different periods of gestation can help to distinguish normal brain from abnormal during different phases of development.⁵ It also helps to make the diagnosis of functional and structural abnormalities earlier.⁶ B-mode or a two-dimensional (2D) US is impossible to understand the complexity of these movements and so till the invent of four-dimensional (4D) US it was not possible to correctly evaluate the fetal movements, especially fetal expressions. The details of fetal face and hands studied by 4D US have potential to generate information regarding fetal movement and behavior.7 There is a specific fetal behavioral pattern that corresponds to each week or trimester of fetal life and this pattern reflects the steps of human brain development and maturation.^8-10