What Does REI Mean?

The Short Answer: REI Is a Subspecialty

On this site, REI means Reproductive Endocrinology and Infertility. It names a subspecialty of obstetrics and gynecology that focuses on the hormonal control of reproduction and on the evaluation and treatment of infertility. Physicians who complete this training are often called REI specialists, reproductive endocrinologists, or fertility specialists, and the credential they earn is certification in Reproductive Endocrinology and Infertility through the American Board of Obstetrics and Gynecology.

If you landed here searching for a quick definition, that is the core of it. The rest of this guide unpacks what the three words in the name signal about the clinical work, how someone becomes an REI, what the certification blueprint covers, and how the exam is structured. If you want other angles on the same question, our companion pieces on what REI is, what REI stands for, and REI meaning cover the terminology from slightly different directions.

Reading the Acronym Word by Word

The name is not decoration. Each term maps to a distinct body of knowledge that the certification expects a specialist to command.

Reproductive

This covers the whole reproductive axis: the hypothalamus, pituitary, ovary, and uterus in women, and the corresponding testicular axis in men. It includes gamete biology, early embryo development, implantation, and the earliest stages of pregnancy. The blueprint's treatment of reproductive physiology across the lifespan reflects how far this word stretches, from pubertal onset through the reproductive years and into the menopausal transition.

Endocrinology

This is the hormonal half of the discipline. REI specialists must understand hormone structure and function, basic pharmacology, and laboratory assays well enough to interpret results and troubleshoot discordant findings. Endocrine conditions that overlap with reproduction, including neuroendocrine disorders, thyroid disorders, and ovarian and adrenal disorders, sit squarely inside the scope.

Infertility

This is the most visible clinical face of the field. It spans evaluation of female and male factors, ovulation induction and other treatments, assisted reproductive technology (ART) techniques, fertility preservation, and the management of recurrent pregnancy loss. Anatomic causes such as fibroids, polyps, adhesions, and congenital anomalies of the reproductive tract belong here too.

Why the Acronym Causes Confusion

"REI" is a three-letter abbreviation shared by several unrelated things in the world, including other professional credentials and even a well-known outdoor retailer. Search results for the bare acronym can therefore wander far from medicine. On this site the meaning is fixed: the subspecialty of Reproductive Endocrinology and Infertility, certified through ABOG. Nothing here describes any other credential that happens to use the same letters, and details such as eligibility, exam structure, and content scope on this page apply only to the ob/gyn subspecialty.

If you are specifically trying to understand the credential, our pages on what REI certification is and the overview at REI certification are good next steps. For a plain phrase-level answer, see what does REI mean and what is a REI.

What an REI Specialist Actually Does

Day to day, the work blends endocrine problem-solving, procedural skill, and counseling. Patients arrive with a wide range of presentations, and the specialist has to sort them into the right diagnostic pathway.

• Evaluating infertility in individuals and couples, including female factors, male factors, and unexplained infertility.
• Managing ovulatory and menstrual disorders, such as those tied to polycystic ovary syndrome, hypothalamic dysfunction, thyroid disease, or abnormal uterine bleeding.
• Performing and directing ART, including the laboratory and clinical sequence that leads to embryo transfer.
• Guiding fertility preservation for patients facing gonadotoxic treatment or choosing to delay childbearing.
• Treating recurrent pregnancy loss and early pregnancy complications.
• Addressing anatomic disease such as endometriosis, adenomyosis, leiomyomas, polyps, Asherman syndrome, and congenital tract anomalies.
• Applying genetic screening and testing to individual patient care.

The Training Path to Becoming an REI

According to the American Society for Reproductive Medicine's 2025 statement on the scope of practice of the subspecialty, the training sequence is long and structured: medical school, a four-year obstetrics and gynecology residency, and then a three-year REI fellowship. That professional-society summary describes the training context; it is not itself an exam blueprint.

For a closer look at eligibility mechanics, see our breakdown of REI requirements. If you are weighing whether the time investment makes sense, REI training and the analysis in is the REI certification worth it frame the decision.

The Six Clinical Domains Behind the Credential

The current ABOG REI blueprint, as linked from the ABOG exam blueprints page, lays out six primary categories and 27 subcategories. It does not print percentage weights, and it does not split coverage between the written and oral stages, so any weighting you see elsewhere, including practice-question allocation on this site, is editorial rather than official. Our complete guide to all six REI content areas goes deeper on each; here is the shape of the map.

Written and Oral: How Certification Works

Certification involves two distinct examinations. The first is a written Qualifying Examination (QE), delivered through Pearson VUE. The second is an oral Certifying Examination (CE). They are separate stages with separate demands, and the common REI blueprint does not assign them separate coverage or weights. Stage-specific numeric logistics, such as fees, item counts, and time limits, are not established by that blueprint and depend on the applicable current ABOG bulletin for each stage, so confirm those directly with ABOG before you plan.

An eligibility change worth knowing

According to an ABOG update presented at the 2026 SMFM Program Directors Meeting, the thesis requirement moves from Certifying Examination eligibility to Qualifying Examination eligibility for fellowship graduates from 2026 onward. Earlier graduates retain their prior requirements. If you are near the transition, read the current ABOG guidance carefully rather than relying on older forum posts.

What the available outcome data shows

The same ABOG presentation reports a 2025 REI first-time Qualifying Examination pass rate of 100% (N=55) and a Certifying Examination pass rate of 94.7% (N=57). The presentation's QE repeat-taker and overall cohort counts are internally inconsistent, so we do not assert a reconciled overall rate. Small cohorts also mean year-to-year variation can be large. For fuller context, see what the REI pass rate data shows and how hard the REI exam is.

Timing in context

The ABOG presentation lists 2026 subspecialty dates of July 20 for the Qualifying Examination and April 13-17 for the Certifying Examination, along with continuing-certification participation to remain certified. Treat those as historical 2026 reference points, not booking promises. Current windows and deadlines are covered in REI exam dates, and what you will pay is in REI certification cost. Scoring details are in REI passing score.

Where REI Specialists Work

REI specialists practice in settings built around reproductive care. The most common are private and group fertility practices, university and academic medical centers, and hospital-affiliated reproductive medicine programs. Academic roles often combine clinical care with teaching and research, while private practice leans toward high-volume ART and consultative care. Some physicians also work in industry or in laboratory-focused leadership roles connected to embryology and andrology services.

Compensation varies widely by setting, region, and practice model, and we do not quote figures here that we cannot source. For a fuller view, read the REI salary guide and the overview of REI jobs.

Sequencing Your Preparation by Domain

Rather than a generic study schedule, build your order around how the domains depend on each other. Foundations first, then the clinical systems that rest on them, then the applied and anatomic material. A reasonable example arc looks like this:

For a fuller plan, see the REI study guide, and keep the REI cheat sheet handy for last-pass review. When you are ready to test yourself against domain-organized questions, the REI practice test mirrors the six-domain structure, and our full question bank lets you drill the areas where you are weakest.

Frequently Asked Questions