BackgroundLetters of recommendation for Maternal-Fetal Medicine(MFM) fellowship are a critical part of the applicant selection process. However, data regarding best practices for how to write LOR for MFM is limited. Similarly, within letters of recommendation, differences in the “code” or meaning of summative words/phrases used at the end of letters of recommendation are seen between surgery, pediatrics, and medicine. However, data regarding code MFM Letters of recommendation are quite limited. ObjectiveWe sought to describe what Maternal-Fetal Medicine program directors value in letters of recommendation for fellowship applicants and how PDs interpret commonly used summative words/phrases. Study DesignAfter IRB exemption, subject matter experts developed an e-survey querying the importance of various letters of recommendation “best practices” described by other specialties. Content and face validation were performed prior to dissemination. This cross-sectional survey was administered to MFM program directors in February 2023. The primary outcome was the relative importance of letters of recommendation content areas. Secondary outcomes included the strength of each summative “code” phrase. Descriptive analysis was performed and principal component analysis (PCA) was then used to reduce the list of phrases to their underlying dimensions. Statistical analysis was performed by SPSS 29.0. ResultsOf 104 MFM program directors sent the survey, 70 (67%) responded. MFM program directors reviewed an average of 78 applications (SD, 30) with 60% writing ≥3 letters/year. Ninety-one percent of respondents noted that letters of recommendation are important/very important in shaping impressions of an applicant. Respondents reported the depth of interaction with an applicant, the applicant's specific behavior traits, the applicant's abilities and a summative statement including strength of the recommendation as important content for MFM fellowship letters of recommendation. Letter length, use of bold/italics, and restating the applicant's curriculum vitae were considered not important. Following PCA with varimax rotation, 14 specific phrases used in letters of recommendation were reduced to 5 themes: high qualitative assessments, average qualitative assessments, objective metrics, exceeding expectations and grit. These themes accounted for 64.6% of the variance in the model (KMO 0.7, Bartlett's Test of Sphericity p<.01). Phrases that respondents considered positive included: “Top 5%,” “Want to keep,” and “highest recommendation,” (all mean score≥4.5/5), while “expected level,” “showed improvement,” and “2nd quartile” were negatively associated code words (all mean score <2.5/5). ConclusionMFM program directors reported that descriptions of an applicant's abilities, behavior traits, and depth of the writer's interactions with the applicant were all important components of an MFM fellowship letters of recommendation. Letter length, bold/italics, and highlights from the CV were not important. A clear “code” emerged regarding summative phrases included in letters of recommendation. Dissemination of these data might help less experienced letter writers send a clearer message and ensure all letter writers have a shared mental model.