While female sex is a robust risk factor for posttraumatic stress disorder (PTSD), pregnant women are an understudied population in regards to PTSD symptom expression profiles. Because circulating hormones during pregnancy affect emotionality, we assessed whether pregnant women would have increased expression of the intermediate phenotypes of hyperarousal and fear-potentiated startle (FPS) compared to non-pregnant women. We examined PTSD symptom profiles in pregnant (n = 207) and non-pregnant women (n = 370). In a second study, FPS responses were assessed in 15 pregnant and 24 non-pregnant women. All participants were recruited from the obstetrics and gynecology clinic at a public hospital serving a primarily African-American, low socioeconomic status, inner-city population. Our results indicate that overall PTSD symptoms were not different between the groups of women. However, pregnant women reported being more hypervigilant (p = 0.036) than non-pregnant women. In addition, pregnant women showed increased FPS to a safety signal compared to non-pregnant women (p = 0.024). FPS to a safety signal in pregnant women was significantly correlated with PTSD hyperarousal symptoms (r = 0.731, p < 0.001). Furthermore, discrimination between danger and safety signals was present in non-pregnant women (p = 0.008), but not in pregnant women (p = 0.895). Together, these data suggest that pregnant women show clinical and psychophysiological hyperarousal compared to non-pregnant women, and support screening for PTSD and assessment of PTSD risk in pregnant women.