The work of professional interpreters is frequently misunderstood and mistrusted, leading to its underuse across healthcare settings. In UK maternity services, this failing contributes to the higher mortality and morbidity of women with limited or no English proficiency. Our study explored interpreters' professional identities and their contribution to the delivery of care in maternity services. Face-to-face interviews with a purposive sample of professional interpreters working in maternity settings were conducted and data analysed using a version of Foucauldian discourse analysis. Our interpretation of the data is that discourses of 'women's work' were used in constructing the interpreters' professional identity. Their daily working practice included affective, social and supportive behaviours; however, their subject positions were unrecognised in the voluntary professional codes of conduct for interpreting practice and their labour remained largely invisible and under-valued. Recognising professional interpreters' identity as invisible labourers suggests that they negotiate biomedical understandings of healthcare interpretation work held by healthcare professionals and women. It allows a more nuanced understanding of interpreters' practice within maternity settings. Making their work visible offers greater opportunity for regulation, monitoring and evaluation, resulting in greater confidence in its quality and promoting increased uptake.