Weight bias toward individuals with higher body weights permeates health care settings in the United States and has been associated with poor weight-related communication and quality of care as well as adverse health outcomes. However, there has been limited quantitative investigation into weight bias among perinatal care providers. Certified nurse-midwives (CNMs)/certified midwives (CMs) attend approximately 11% of all births in the United States. The aims of this study were to measure the direction and extent of weight bias among CNMs/CMs and compare their levels of weight bias to the US public and other health professionals. Through direct postcard distribution, social media accounts, professional networks, and email listservs, American Midwifery Certification Board (AMCB)-certified midwives were solicited to complete an online survey of their implicit weight bias using the Implicit Association Test and their explicit weight bias using the Antifat Attitudes Questionnaire, Fat Phobia Scale, and Preference for Thin People measure. A total of 2257 midwives participated in the survey, yielding a completion rate of 17.7%. Participants were mostly White and female, with a median age of 46 years and 11 years since AMCB certification. More than 70% of midwives have some level of implicit weight bias, although to a lesser extent compared with previously published findings among the US public (P <.01) and other health professionals (P <.01). In a subsample comparison of female midwives to female physicians, implicit weight bias levels were similar (P >.05). Midwives also express explicit weight bias, but at lower levels than the US public and other health professionals (P <.05). This study provides the first quantitative research documenting weight bias among a national US sample of perinatal care providers. Findings can inform educational efforts to mitigate weight bias in the perinatal care setting and decrease harm.