Although the discussion so far has been limited to a unidirectional relationship from pregnant woman to fetus, the fetus is an active contributor to its own epigenesis within the uterine environment . Previously, we demonstrated in two economically and ethnically diverse samples (in Lima, Peru, and Baltimore, MD), measured longitudinally from the 20th to the 38th week of gestation, that spontaneous fetal motor activity transiently stimulates maternal sympathetic arousal [86]. These findings were based on time-series analyses of contemporaneous maternal– fetal recordings during undisturbed periods of maternal rest during which time fetal movements were observed to generate an increase in maternal heart rate and electrodermal activity within 2–3 seconds after the spontaneous fetal movement. Recently, we have demonstrated the same phenomenon using an experimental model in which a fetal motor response was elicited by an external stimulus and generated a maternal physiological response consistent with an orienting response (J. DiPietro et al, unpublished data, 2012). Despite the ubiquity of the stimulus (i.e., fetuses move, on average, about once per minute in pregnancy), the indication is that women do not physiologically habituate or become desensitized to fetal movements. Although we have speculated that such fetal signaling prepares pregnant women for infant caretaking, we include it here as a reminder that the maternal–fetal interface is bidirectional with largely unknown repercussions. Could, for example, natural variation in levels of fetal motor activity generate variation in feelings of psychological stress in pregnant women?