This study examined the likelihood of giving birth to a daughter as a function of women's exposure to four categories of stressors: childhood trauma, adult trauma, chronic stressors, and recent (adverse) life events. Hypothesis 1 stated that exposure to recent life events (near conception) and to childhood traumas would increase women's chances of having a girl baby. Hypothesis 2 stated that the relationship between stress and gender outcome is mediated by persistent posttraumatic stress disorder (PTSD) symptoms. The final sample was comprised of 225 women. The design was prospective observational. At first contact, women were retained if they were <27 weeks pregnant and met initial inclusion criteria. In interview 2, at 27-30 weeks, women were excluded for positive diagnoses of anxiety disorders besides PTSD with or without depression (Structured Clinical Interview for DSM-IV Disorders). In interview 3 (30-34 weeks), reports on stress categories (Social Stress Indicator Questionnaire) and PTSD symptoms (Post-Traumatic Checklist) were obtained. Infant gender was obtained from medical records. The relationship between stress categories and the distribution of girl/boy infants was examined with Chi Squares and logistic regression analyses. Mediation was tested with the macro PROCESS (Hayes 2012). Childhood trauma was the only stress category that increased the odds of having a girl, with an odds ratio of >3.0 for women who had been exposed to more than two such events. PTSD symptoms (partially) mediated the relationship between childhood trauma and infant gender. Findings suggest that women's exposure to childhood trauma contributes to the determination of the sex ratio at birth and that PTSD symptoms are part of the cause.