With Black women facing disproportionately worse health outcomes during and after pregnancy, innovations in digital mental health provide an avenue to support the mental wellbeing of this population. Importantly, the advent of social media and its popularity among perinatal Black women for mental health, highlights social platforms as an avenue to learn about this population's stress expression and coping behaviors. We report the results of a mixed method study analyzing how stress experiences and coping patterns manifest online among 114 Black women (M age = 30.2) during and after pregnancy. By triangulating the results of survey and social media data analyses, we find that while participants experience stress, there exists a disconnect between their reported stress experiences in their survey data and their disclosures of stress on social media. Notably, while participants (n=17) reported experiencing moderate to high levels of perceived stress, they rarely discuss this stress in their social media posts. Using the stress process model and Superwoman schema to guide our analysis, we highlight patterns in online stress disclosure and coping from our participants, and offer implications of our findings for the design of digital mental health interventions.