Introduction: Pregnancy has been associated with diminished maternal mental health and a deterioration in partner relationship quality. The recent COVID-19 quarantine measures have created additional stressors for pregnant women due to isolation and a surge in partner conflict. Objective: The purpose of this study was to assess how partner relationship conflict and social support may mediate mental health outcomes during the COVID-19 lockdown. Methods: A cross-sectional study with a sample of 152 pregnant women using psychological measures, (i.e. Prenatal Distress Questionnaire, Symptom Checklist-90-R, Duke-UNC-11 Functional Social Support Questionnaire, Perceived Stress Scale). Demographic characteristics, obstetrics history, and partner relationship conflict were assessed using questionnaires. Results: While there were few reports of physical violence in this sample, between 18% and 59% of women reported partner relationship conflict on the psychological subscale (e.g. afraid of one’s partner or screamed at by one’s partner). Further, the psychological subscale was significantly associated with symptoms of psychopathology. There was a significant negative association between social support and pregnancy-specific stress (p = .005), and perceived stress (p= .038). Conclusions: These findings suggest that partner relationship conflict and social support may act as important buffers for prenatal mental health in childbearing women during vulnerable situations, such as the COVID-19 pandemic.