In a longitudinal study of fetal ontogeny, DiPietro et al. assessed fetal variables in relation to pregnant women’s reports of daily stress at 6 testing sessions beginning at 20 weeks and ending at 36–68 weeks gestation [19]. Fetuses of mothers who reported greater stress showed significantly lower FHR variability than the low stress group, which suggests that exposure to maternal psychological distress may contribute to diminished parasympathetic control of the fetal heart [19]. Similarly, fetuses of women suffering from maternal depression have displayed higher baseline FHR and a delayed FHR response to stimulus. In a fetal reactivity study, Allister et al. monitored fetal behavior in women with untreated depression and controls at 32–36 weeks gestation during a baseline period, a period of fetal stimulation via a vibroacoustic stimulus administered to the mother’s abdomen, and during a recovery period [20]. Fetuses of depressed mothers displayed a higher baseline FHR, a slower FHR reaction to the external stimulus, and a longer period to return to FHR baseline levels following the stimulus compared to fetuses in a control group [20].