BACKGROUND Despite increased attention to the role of antenatal maternal psychological stress in postnatal development, remarkably little information is available on the nature of the intrauterine fetal response to maternal psychological state. OBJECTIVE To determine whether: (1) the fetus responds to maternal stress; (2) the fetal response changes over gestation; and (3) individual maternal and fetal response patterns are stable over time. METHODS Induced maternal stress at 24 and 36 weeks gestational age using the Stroop color-word task. METHODS 137 low-risk pregnant women with normally developing fetuses. METHODS Maternal (heart rate and skin conductance) and fetal (heart rate, heart rate variability, and motor activity) responses. RESULTS The manipulation evoked maternal sympathetic activation, which declined in magnitude from 24 to 36 weeks gestation. Fetuses responded to the manipulation with increased variability in heart rate (F(2,256)=7.80, p<0.001) and suppression of motor activity (F(2,216)=15.47, p<0.001). The magnitude of the fetal response increased over gestation. The degree of maternal reactivity to and recovery from the stressor were correlated over time (r's=0.53 and 0.60 for heart rate; r's=0.31 and 0.36 for skin conductance; p's<0.001). There was moderate stability in the magnitude of the fetal motor response (r=0.25, p<0.01). CONCLUSIONS Demonstration of fetal responses to maternal sympathetic activation evoked by a benign cognitive stressor suggests that fetal neurobehavioral regulation is routinely disrupted by maternal environmental intrusions. There is no evidence of a protective effect of diminished maternal sensitivity to stress on the fetus. Individual stability in the magnitude of the evoked maternal physiologic and psychological responses from 24 to 36 weeks and stability in the fetal motor response implies that characteristic response patterns emerge in utero. We propose that autonomic development is partially entrained through these processes.