From a large sample of fetuses examined through three-and four-dimensional ultrasonography at different gestational ages, episodes in which distress expressions were recognizable were extracted and analyzed using Baby FACS (Oster, 2009). Coders first identified AU4 (brow knotting) produced by the depressor glabellae (procerus) and the depressor supercilii muscles. This facial action knots the brow due to lowering of glabella. Its presence (except with a strong AU9 in AU9+AU12) has been used as criterion to recognize a distress episode. Then coders described all facial actions that co-occurred with the presence of brow knotting (AU4), distinguishing it from the knitting of the brow due to medial contraction by the isolated action of the corrugator supercilii muscle (AU3; brow knitting). Ultrasonographic examination of the fetal face (from 15 to 24 FPS) was conducted by using a Voluson 730 (Kretztechnik, Zipf, Austria) and an abdominal transducer of 5MHz. The data analyzed to date suggest that distress expressions are exhibited very early in prenatal development, at least from 20 weeks of gestational age, and that their form is very similar, if not identical, to distress expressions observed in full term neonates. This means that a fundamental facial expression important in early mother-infant communication emerges as an organized motor pattern very early in development, well before the possibility of serving as an interactive signal
