What Does REI Stand For?

The Short Answer: Reproductive Endocrinology & Infertility

On this site, REI stands for Reproductive Endocrinology & Infertility. It is a subspecialty of obstetrics and gynecology focused on the hormonal regulation of reproduction, the evaluation and treatment of infertility, and the medical and surgical management of conditions that impair conception and early pregnancy. Physicians who complete the pathway are certified by the American Board of Obstetrics and Gynecology (ABOG).

The acronym is shared by other, unrelated credentials and organizations, so it is worth being precise. Everything on this page concerns the physician subspecialty and its ABOG certification, nothing else. If you want a broader orientation, our explainers on what REI is and the meaning of REI cover adjacent angles, and what REI certification involves goes deeper on the credential itself.

Why the Name Has Three Parts

Each word in the title points to a different strand of the discipline, and the exam reflects all three.

• Reproductive: the physiology of gametes, embryos, the endometrium, and early pregnancy, from folliculogenesis through implantation and the first trimester.
• Endocrinology: hormone structure and function, pharmacology, laboratory assays, and disorders of the hypothalamic-pituitary-ovarian axis, thyroid, and adrenal glands.
• Infertility: the clinical work of evaluating couples, treating ovulatory and tubal factors, managing male-factor problems, and delivering assisted reproductive technology (ART).

Candidates sometimes assume the subspecialty is mostly in vitro fertilization. In reality, the endocrine foundation carries enormous weight, and a large portion of the blueprint concerns physiology, assays, and endocrine disease rather than laboratory procedures.

What an REI Subspecialist Actually Does

The clinical scope extends well beyond fertility treatment. According to the ASRM scope-of-practice statement on the REI subspecialist, the field spans reproductive endocrine disorders, infertility evaluation and treatment, and fertility preservation. In day-to-day practice that translates into several recognizable patterns:

• Diagnosing and managing ovarian and adrenal disorders, neuroendocrine problems, and thyroid disease as they affect reproduction.
• Evaluating abnormal uterine bleeding and endometrial physiology.
• Working up recurrent pregnancy loss and managing early pregnancy complications.
• Treating anatomic disease such as endometriosis, adenomyosis, fibroids, polyps, adhesions, congenital tract anomalies, and Asherman syndrome.
• Counseling on genetic screening and testing and applying results to patient care.
• Preserving fertility for patients facing gonadotoxic treatment or other threats to reproductive potential.

The Training Path Behind the Acronym

The ASRM 2025 scope-of-practice statement describes the standard route into the subspecialty: medical school, a four-year obstetrics and gynecology residency, and then a three-year REI fellowship. That professional-society summary describes training context; it is not an ABOG exam blueprint, and the two should not be conflated.

For a deeper treatment of who qualifies to sit for the examinations, see our guide to REI requirements, eligibility, and prerequisites, and for a view of what fellowship preparation looks like, REI training is a useful companion.

The Six Content Domains Under the Label

ABOG's currently linked REI blueprint organizes the subspecialty into six primary clinical categories and 27 subcategories. The document does not print percentage weights, and it does not allocate content separately between the written and oral stages. Treat the six domains below as a map of scope rather than a weighted pie chart. Our full walk-through is in REI Exam Domains 2026: Complete Guide to All 6 Content Areas.

The Two-Stage ABOG Exam

REI certification is not a single sitting. It retains a written Qualifying Examination (QE), delivered through Pearson VUE, and an oral Certifying Examination (CE). They are different experiences testing the same body of knowledge in different ways, and the credential should not be renamed to either stage alone.

One recent policy change matters for anyone finishing fellowship now. According to ABOG's 2026 update to subspecialty program directors, the thesis moves from CE eligibility to QE eligibility for fellowship graduates from 2026 onward. Earlier graduates retain their prior requirements. Always confirm current details in the applicable QE or CE bulletin, because stage-specific numeric logistics such as question counts and timing are not established by the common blueprint.

The same presentation lists 2026 dates for reference: the subspecialty QE on July 20 and the CE during April 13-17. Those are historical 2026 dates, not an invitation to book. For scheduling mechanics, see REI exam dates, testing windows, and deadlines; for fees, REI certification cost; and for scoring, REI passing score.

What the 2025 Outcome Data Say

The ABOG update to program directors reports a 2025 REI first-time QE pass rate of 100% (N=55) and a CE pass rate of 94.7% (N=57). The presentation's QE repeat and overall cohort counts are internally inconsistent, so we do not assert a reconciled overall rate. Small cohorts also mean these figures can swing sharply from year to year. For context on how to read them, see REI pass rate: what the data shows and how hard the REI exam is.

High pass rates do not mean the content is easy. Candidates reaching this stage have already passed Ob/Gyn boards, completed demanding fellowships, and been selected through a competitive process. The examinations are calibrated against a highly prepared group.

Where REI Subspecialists Work

Certification opens several practice settings. Without inventing figures, the common employers and structures include:

• Private fertility practices and networks offering evaluation, ovulation induction, intrauterine insemination, and IVF.
• Academic medical centers combining clinical care, fellowship teaching, and research.
• Hospital-affiliated reproductive medicine programs serving both fertility and endocrine patients.
• Fertility preservation programs coordinating with oncology and other services.

Compensation and job-market questions deserve their own treatment: our REI salary guide, the analysis of whether REI certification is worth it, and a look at REI jobs take those up directly.

Sequencing Your Preparation by Domain

General study habits matter less than ordering the content sensibly. The domains build on each other, so a logical sequence runs from foundations outward to clinical application.

When you are ready for full coverage, work through our REI study guide, keep the REI cheat sheet nearby for last-minute review, and test your recall with the REI practice test bank. Remember that any practice-question allocation across domains is editorial rather than an official weighting, so use it for balanced coverage, not for predicting emphasis. You can also start from the main REI Exam Prep site to browse available question sets, and read the overview of REI certification if you are still deciding whether to pursue it.

Frequently Asked Questions