Fetal movements with their associated FHR accelerations, as well as the cyclic alternation between episodes of low and high FHR variability, particularly in late pregnancy, give a clear indication of the fetal rest-activity cycle. FHR variability changes during labor indicate that the rest-activity cycle continues even though perceived movements may diminish and fetal breathing may stop. Fetal behavioral states, known to be present by term and characterized by the concordant association of fetal movements, continue during labor. However, not all labors show evidence of fetal behavior despite a normal outcome, and the significance of this remains unknown. The influence of the fetal rest-activity cycle on FHR variability is such that recognition of behavioral cycles, when present, is essential for appropriate interpretation of the FHR during labor.