Online patient communities have proliferated rapidly, as has literature exploring the role such communities play in allowing patients to share knowledge, offer support to one another, and advocate for better medical care. Yet there has been limited scholarly engagement with patient community in gestational diabetes (GDM). Drawing on a grounded theory analysis of 18 semi-structured interviews with women with GDM, I explore how participating in an online GDM support community shaped these women’s experiences of pregnancy and illness. Women’s interactions with one another prompted them to appraise, contest, and co-create knowledge claims about GDM. Those in the community supported each other through the difficulties of GDM, but also held each other accountable to their regimes of self-management, often to a greater extent than their health professionals. The networks of peer support within the community engendered new ethics of care and responsibility, reframing GDM as a condition worthy of more personalised treatment and increased medical attention. These findings attest to the emergence of patient-led biocitizenship in GDM, although a caveat is given that these participants all had access to resources that facilitated their engagement with self-care practices. Further research should explore GDM patient community in marginalised populations.