Stylianos (Stelios) Vagios, MD, PhD, a Vincent fellow in Reproductive Endocrinology and Infertility (REI), investigates how hormone-producing cells within the ovarian stroma contribute to hormone production across the human lifespan. While traditional models emphasize follicles as the primary source of ovarian hormones, emerging evidence suggests that stromal cells may play an underrecognized endocrine role — particularly during periods of low follicular activity, such as before puberty and after menopause. Using single-cell transcriptomics, Dr. Vagios is investigating how stromal cell populations vary with age and pathological states, such as polycystic ovary syndrome (PCOS). By defining stromal–follicular crosstalk, his work aims to improve fertility preservation strategies and identify new approaches to support hormonal health in reproductive aging and menopause. Clinically, he conducts research leveraging artificial intelligence to improve embryo selection and predict fertility treatment outcomes. In parallel, he investigates metabolomic signatures in PCOS to better understand its systemic metabolic and reproductive effects. Together, his work bridges ovarian biology, data science and clinical care to improve reproductive and long-term women’s health.

Faculty Mentors
Basic Research
David Pepin, PhD, Associate Professor, Associate Molecular Biologist, Associate Director, Mass General Pediatric Surgical Research Laboratorie

Clinical Research
Irene Souter, MD, Vincent OB/GYN Division of REI
Charles Bormann, PhD, Vincent OB/GYN Division of REI, Director of Mass General Brigham IVF Laboratory
Shruthi Mahalingaiah, MD, Vincent OB/GYN Division of REI
Irene Dimitriadis, MD, Vincent OB/GYN Division of REI
John Petrozza, MD, Vincent OB/GYN Division of REI
Victoria Fitz, MD, Vincent OB/GYN Division of REI

Career Path
MD:  University of Athens School of Medicine, 2011–2017
PhD:  University of Athens School of Medicine, 2018–2022
Research Fellowship:  Mass General Hospital, 2019–2021
OB/GYN Residency:  Tufts Medical Center, 2021–2025
Vincent Fellowship:  2025–2028

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Alexa Sassin, MD, a Vincent fellow in Reproductive Endocrinology and Infertility, performs research to better understand the pathophysiology of reproductive disorders and to improve clinical outcomes for infertility patients. She is particularly interested in polycystic ovary syndrome (PCOS), a common endocrine disorder estimated to affect up to 6–15% of reproductive-aged women. In the basic science laboratory, she investigates how disruptions in ovarian cell signaling — especially within the Anti-Müllerian Hormone (AMH) pathway — contribute to PCOS. By exploring how intracellular signaling cascades are altered in PCOS, she hopes to uncover potential therapeutic targets and identify downstream micro-RNAs impacted by the disorder. Additionally, her research examines the in utero effects of PCOS on patients who ultimately conceive through fertility treatments, examining how PCOS impacts placental development. Clinically, Dr. Sassin is involved in several studies aimed at helping infertility patients achieve healthy pregnancies, including early identification of patients who may be at risk of obstetrical complications such as pre-eclampsia or preterm delivery. Another aspect of her clinical research analyzes the influence of social determinants of health on fertility care. Through this work, she aims to promote equitable access to infertility care and expand treatment opportunities for diverse patient populations.

Faculty Mentors
Basic Research
David Pepin, PhD, Associate Professor, Associate Molecular Biologist, Associate Director, Mass General Pediatric Surgical Research Laboratories
Patricia Donahoe, MD, Director, Mass General Pediatric Surgical Research Laboratories

Clinical Research
Irene Souter, MD, Vincent OB/GYN Division of Reproductive Endocrinology and Infertility (REI)
Charles Bormann, PhD, Embryology Lab Director, Vincent OB/GYN Division of REI
Shruthi Mahalingaiah, MD, Vincent OB/GYN Division of REI
John Petrozza, MD, Vincent OB/GYN Division of REI
Lidia Minguez Alarcon, PhD, Assistant Professor of Medicine at Harvard Medical School, Brigham and Women’s Hospital, and Harvard TH Chan School of Public Health

Career Path
MD:  Baylor College of Medicine, 2013–2017
OB/GYN Residency:  Baylor College of Medicine, 2017–2021
Women’s Reproductive Health Research (WRHR) Scholar:  Baylor College of Medicine, 2021–2024
Vincent Fellowship:  2024–2027

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Christopher Ke Arkfeld, MD, a Vincent fellow in Reproductive Endocrinology and Infertility, is participating in both translational basic science and clinical research. In the basic science lab, he is building on the foundation of past fellows by investigating the role of anti-Müllerian hormone (AMH) on human pre-implantation embryos across different infertility diagnoses, including polycystic ovarian syndrome, a common hormonal disorder of women of reproductive age that causes ovarian cysts, irregular periods and infertility. His work will help provide one of the largest cohorts of genetically sequenced human embryos in the published literature. Clinically, his research interests are aimed at improving patient experiences and outcomes at Mass General’s Fertility Center. He is currently researching the indirect costs of fertility treatment and re-evaluating the World Health Organization’s guidelines regarding semen sample production.

Faculty Mentors
Basic Research
David Pepin, PhD, Associate Professor, Associate Molecular Biologist, Mass General Pediatric Surgical Research Laboratories
Patricia Donahoe, MD, Director, Mass General Pediatric Surgical Research Laboratories

Clinical Research
Charles Bormann, PhD, Embryology Lab Director, Vincent OB/GYN Division of Reproductive Endocrinology
Victoria Fitz, MD, Vincent OB/GYN Division of Reproductive Endocrinology and Infertility

Career Path
MD:  University of Nebraska Medical Center, 2015–2019
OB/GYN Residency:  Yale University, 2019–2023
Vincent Fellowship:  2023–2026

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