What Is A REI?

What "REI" Means in Medicine

In this context, 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 disorders that disrupt reproductive function across a woman's lifespan. A physician who completes the training and board certification in this field is called a reproductive endocrinologist, often shortened in conversation to "an REI."

The acronym is shared with unrelated credentials and organizations in other industries, so it is worth being precise: everything on this page concerns the physician subspecialty certified through the American Board of Obstetrics and Gynecology (ABOG). If you are searching for the plain-language definition of the term, our companion pieces on what REI is, what REI stands for, and REI meaning cover the vocabulary angle. This article focuses on what the role is, how physicians qualify for it, and what the credentialing process tests.

What a Reproductive Endocrinologist Actually Does

The title sounds narrow, but the clinical scope is broad. A reproductive endocrinologist manages two overlapping bodies of work: reproductive endocrine disease (conditions driven by hormonal dysregulation) and fertility care (helping patients conceive, and preserving the ability to conceive later).

Endocrine and gynecologic disease

Many patients arrive not for infertility but for a hormonal or structural problem. The blueprint's subcategories give a realistic picture of this caseload:

• Neuroendocrine disorders, thyroid disorders, and disorders of the ovary and adrenal gland
• Endometrial physiology and abnormal uterine bleeding
• Endometriosis, adenomyosis, leiomyomas, and endometrial polyps
• Pelvic adhesive disease and Asherman syndrome
• Congenital anomalies of the reproductive tract

Infertility evaluation and treatment

On the fertility side, the work spans evaluation of female and male factors, ovulation-focused treatment, and assisted reproductive technology (ART) techniques. It also includes fertility preservation for patients facing gonadotoxic treatment or choosing to delay childbearing, and management of early pregnancy complications and recurrent pregnancy loss.

Laboratory and genetic literacy

Unlike many procedural subspecialties, REI practice depends heavily on interpreting laboratory data, understanding gamete and early embryo biology, and counseling patients about genetic testing and screening. That blend of bench-level physiology and bedside counseling is what distinguishes the field.

The Training Pathway: Residency, Fellowship, Board Certification

According to the ASRM 2025 scope-of-practice statement on the REI subspecialist, the typical United States pathway is medical school, followed by a four-year residency in obstetrics and gynecology, followed by a three-year REI fellowship. That is a professional-society summary of training and scope, not an exam blueprint, but it accurately frames how long the road is.

Eligibility details, such as prerequisites and what counts toward qualification, are summarized in our guide to REI requirements. For a career-oriented view of the fellowship years themselves, see REI training.

The Six Domains of REI Clinical Knowledge

ABOG publishes a single common REI blueprint. The version currently linked from its exam-blueprint index contains six primary categories and 27 subcategories. It does not print percentage weights, and it does not split coverage between the written and oral stages. The domain names below track those six categories. For a deeper treatment of each, read our complete guide to the six REI content areas.

The Two-Stage ABOG Examination

Certification in this subspecialty retains both a written and an oral component:

• Qualifying Examination (QE): a written, computer-based examination delivered through Pearson VUE.
• Certifying Examination (CE): an oral examination, a distinct experience from the written test.

These are two different exams with different formats, and the common blueprint does not assign separate coverage or weights to each. Any allocation of practice questions you see in prep materials, including ours, is editorial judgment rather than an official weighting. Stage-specific logistics such as fees, registration windows, and exact scheduling belong to the applicable current QE or CE bulletin, so verify them there before you plan. Our breakdowns of REI certification cost and REI exam dates discuss the planning side in more detail.

How the oral stage changes your preparation

The written exam rewards breadth and recall under time pressure. The oral exam rewards the ability to reason aloud: defending a diagnostic pathway, explaining why you would choose one protocol over another, and handling a complication scenario. Candidates who prepare only with multiple-choice recall often feel underprepared for the conversation format. Practicing explanation, not just selection, matters.

Historical 2026 dates

ABOG's presentation lists the 2026 subspecialty QE on July 20 and CE during April 13-17, and notes that continuing-certification participation is required to remain certified. Treat those as historical reference points, not booking promises; always confirm current dates with the issuer. See REI certification and what REI certification is for the broader credential picture.

What the Issuer Reports About Pass Rates

ABOG's update to fellowship program directors reports, for 2025:

Two cautions apply. First, the same presentation's QE repeat-taker and overall cohort counts are internally inconsistent, so we do not assert a reconciled overall pass rate. Second, these are small cohorts drawn from a self-selected group of fellowship graduates, so a high pass rate reflects a heavily trained population rather than an easy test. For interpretation, see our discussions of the REI pass rate, how hard the REI exam is, and the passing score.

Where REI Subspecialists Work and Who Hires Them

Reproductive endocrinologists practice in several settings, and the employer shapes the day-to-day work considerably:

• Private fertility practices and clinic networks: volume-oriented ART centers with embryology laboratories on site.
• Academic medical centers: a mix of patient care, fellowship teaching, and research.
• Hospital-affiliated reproductive medicine programs: often integrated with gynecologic surgery and high-risk services.
• Fertility preservation and oncofertility programs: collaborating with oncology teams to counsel patients before treatment.

Because REI practice often includes procedures, laboratory oversight, and complex counseling, employers value both certification and demonstrated clinical skill. Explore the market in our REI jobs overview, and review compensation context in the REI salary guide. If you are weighing the whole commitment, is the REI certification worth it lays out the trade-offs.

Sequencing Your Preparation Around the Blueprint

Rather than studying in textbook order, consider ordering the six domains by dependency: foundational science first, because later domains assume it. A sensible progression looks like this.

Because the blueprint gives no weights, avoid over-investing in your favorite domain at the expense of the others. For a fuller plan, see the REI study guide and the one-page REI cheat sheet, and test yourself against realistic questions in our REI practice test.

Where to Go Next

If you landed here searching variations of the same question, such as what is a REI or what does REI mean, the short answer is a physician subspecialist in reproductive endocrinology and infertility. The longer answer is a multi-year training path, a two-stage board process, and a clinical scope that spans endocrinology, surgery, laboratory science, and genetics. When you are ready to move from definitions to preparation, begin with a few timed sets on the main practice test site to see which domains need the most attention.

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