An abrupt, generalised and stereotyped movements, typically occurring spontaneously during quite sleep (fatal state 1F) and transitions between sleep states, and always starting in the limbs and often spreading to the trunk and neck. Fetuses begin to express this movement pattern at 8.5-10 weeks of gestation (see figure below).
Fetal startles with a first age of appearance of 8.5-10 weeks of gestation, these movements mostly occur as single events lasting about 1 second. They may sometimes follow each other in rapid succession with an interval of a few seconds between them, and be powerful enough to lift the fetus from the lying surface. As with hiccups, stretches and yawns, these complex movements persist throughout the life span without changing their pattern. The black line stands for the median and the tray lines for the interquartile range. For 8 to 19 weeks, figure adapted from de Vries, J.I.P., Visser, G.H.A., & Prechtl, H.F.R. (1985). The emergence of fatal behaviour. II. Quantitative aspects. Early Human Development, 15, 333-34 8 for 8 to 19 weeks, and for 20 to 36 weeks from Roodenburg, P.J., Wladimiroff, J.W., van Es, A., & Prechtl, H.F.R. (1991). Classification and quantitative aspects of fatal movement during the second half of pregnancy. Early Human Development, 25, 19-35.
See General movements, Hiccups, Startles, Stretches