- What REI Means in This Context
- The Training Path Behind the Abbreviation
- What an REI Subspecialist Actually Does
- How ABOG Certifies the Subspecialty
- The Six Content Domains
- Concrete Topics a Candidate Must Master
- What the Published Outcome Data Shows
- Sequencing Preparation Around the Domains
- Where REI Subspecialists Work
- Frequently Asked Questions
- REI stands for Reproductive Endocrinology & Infertility, an obstetrics and gynecology subspecialty certified by the American Board of Obstetrics and...
- Training runs through medical school, a four-year ob/gyn residency, and a three-year REI fellowship.
- Certification has two parts: a written Qualifying Examination (QE) and an oral Certifying Examination (CE).
- The issuer blueprint lists six primary categories and 27 subcategories, with no published percentage weights.
What REI Means in This Context
REI is the standard abbreviation for Reproductive Endocrinology & Infertility, a subspecialty of obstetrics and gynecology. Physicians in this field evaluate and treat hormonal disorders of the reproductive system, difficulty conceiving, recurrent pregnancy loss, and a range of anatomic conditions that affect fertility. They also provide assisted reproductive technology (ART), including in vitro fertilization, and counsel patients on fertility preservation.
On this site, REI refers only to that medical subspecialty and its board certification. If you are searching for the broader definition, our companion pieces What Is REI? and What Does REI Stand For? cover the same ground from different angles, while What Does REI Mean? answers the shorthand question directly.
The Training Path Behind the Abbreviation
An REI subspecialist is first a fully trained obstetrician-gynecologist. The professional-society summary in the ASRM 2025 scope-of-practice statement describes the pathway as medical school, then a four-year obstetrics and gynecology residency, then a three-year REI fellowship. That is a long runway, and it shapes how the certification exam is written: candidates are expected to bring general ob/gyn judgment and layer deep subspecialty knowledge on top of it.
If you are mapping your own timeline, REI Training walks through the fellowship stage, and REI Requirements 2026: Eligibility, Prerequisites & How to Qualify covers what you need to sit for the board examinations.
Medical School
- Foundation in physiology, pharmacology, and clinical medicine
Four-Year Ob/Gyn Residency
- General obstetrics and gynecology training and primary board certification
Three-Year REI Fellowship
- Subspecialty clinical, laboratory, and research training
- Preparation for the QE and CE
What an REI Subspecialist Actually Does
The day-to-day work is a mix of medical endocrinology, procedural gynecology, and laboratory-adjacent decision making. A single clinic day might include an adolescent with delayed puberty, a woman with irregular cycles and suspected ovarian dysfunction, a couple with unexplained infertility, a patient with recurrent pregnancy loss, and a cancer patient who needs fertility preservation before treatment.
- Diagnosis: Interpreting hormone assays, imaging, semen analysis, and genetic results to find the cause of reproductive dysfunction.
- Medical management: Ovulation induction, treatment of thyroid and neuroendocrine disorders, and management of abnormal uterine bleeding.
- Procedures: ART techniques, and evaluation and treatment of structural problems such as polyps, adhesions, and congenital anomalies.
- Counseling: Genetic screening, treatment options, and fertility preservation decisions.
For a look at the professional landscape this training leads into, see REI Jobs.
How ABOG Certifies the Subspecialty
The credential is issued by the American Board of Obstetrics and Gynecology. It has two distinct stages, and it is important not to blur them together:
| Element | Qualifying Examination (QE) | Certifying Examination (CE) |
|---|---|---|
| Format | Written examination | Oral examination |
| Delivery | Delivered through Pearson VUE | Oral format administered by ABOG |
| Published blueprint | Common REI blueprint, no separate QE weights | Same common REI blueprint, no separate CE weights |
| Thesis timing | Required for fellowship graduates from 2026 onward at QE eligibility | Earlier graduates retain prior requirements |
One notable change: the issuer's 2026 update to program directors confirms that the thesis requirement moves from CE eligibility to QE eligibility for fellowship graduates from 2026 onward. Earlier graduates keep their previous requirements. If your graduation year sits near that boundary, verify your exact obligations directly with ABOG.
After certification, ABOG expects continuing-certification participation to remain certified. For the bigger picture of the credential itself, see REI Certification and What Is REI Certification?.
The Six Content Domains
The current issuer blueprint, retrieved from the ABOG exam blueprints page, groups content into six primary clinical categories and 27 subcategories. It does not publish percentage weights, and it does not split coverage between the QE and CE. Our domain names below follow those six categories.
Domain 1: Foundational Reproductive Endocrinology
The scientific base everything else rests on.
- Hormone structure and function
- Basic pharmacology
- Laboratory assays
Domain 2: Reproductive Endocrine Function and Disease
Normal and disordered endocrine physiology.
- Reproductive physiology across the lifespan
- Neuroendocrine and thyroid disorders
- Endometrial physiology and abnormal uterine bleeding
- Ovarian and adrenal disorders, idiopathic and iatrogenic
Domain 3: Conception and Pregnancy: Physiology and Pathology
From gametes through early gestation.
- Gamete biology and early embryo development
- Endocrinology of pregnancy
- Early pregnancy and recurrent pregnancy loss
Domain 4: Fertility and Infertility
The clinical heart of the subspecialty.
- Female fertility and infertility; male infertility
- Special considerations in fertility treatment
- ART techniques and fertility preservation
Domain 5: Anatomic Reproductive Disorders
Structural conditions that impair reproduction.
- Pelvic adhesive disease, endometriosis, adenomyosis
- Congenital anomalies of the reproductive tract
- Asherman syndrome, leiomyomas, endometrial polyps
Domain 6: Reproductive Genetics
Testing, screening, and their clinical use.
- Understanding genetic testing and screening
- Applying genetic screening and testing to patient care
A deeper walkthrough lives in REI Exam Domains 2026: Complete Guide to All 6 Content Areas.
Concrete Topics a Candidate Must Master
Because the blueprint is organized by clinical category, the most productive way to think about content is as clusters of linked reasoning rather than isolated facts.
Endocrine reasoning
Expect to move fluidly between the hypothalamic-pituitary-ovarian axis, thyroid physiology, and adrenal contributions to reproductive dysfunction. Laboratory assays deserve their own attention: knowing what a test measures, what can confound it, and when a result should change management is a recurring theme in Domain 1 and carries into Domain 2.
Treatment decision-making
Domain 4 asks you to choose and justify among options for female and male factor infertility, to recognize special treatment considerations, and to understand ART techniques and fertility preservation. Pharmacology from Domain 1 returns here in applied form.
Anatomy and pathology
Domain 5 rewards candidates who can connect a structural diagnosis to its reproductive consequence and to the right intervention, whether that involves adhesions, Asherman syndrome, polyps, fibroids, or congenital tract anomalies.
Early pregnancy and loss
Domain 3 links endocrinology of pregnancy with early pregnancy complications and recurrent loss, and it connects naturally to the genetics content in Domain 6.
Key Takeaway
Domain 4 is where most clinical reasoning converges, but it depends on Domains 1, 2, and 5. Treat the six domains as one connected system, not six separate lists.
For a compact refresher once you have built that foundation, keep REI Cheat Sheet 2026: One-Page Review of Must-Know Facts nearby.
What the Published Outcome Data Shows
The issuer's 2026 update to fellowship program directors reports two figures for 2025: a first-time QE pass rate of 100% (N=55) and a CE pass rate of 94.7% (N=57). The same presentation contains QE repeat and overall cohort counts that are internally inconsistent, so we do not assert a reconciled overall rate. Small cohorts also mean these numbers should be read as a snapshot, not a guarantee.
To see how to interpret them responsibly, read REI Pass Rate 2026: What the Data Shows, and for the scoring side of things, REI Passing Score 2026: Exactly What You Need to Pass. If you are weighing difficulty, How Hard Is the REI Exam? Complete Difficulty Guide 2026 offers context.
Sequencing Preparation Around the Domains
Because there are no published weights, no domain should be treated as disposable. A sensible order builds from foundations outward, so that clinical domains later in the sequence reuse what you have already consolidated.
Domain 1 first
- Hormone function, pharmacology, and assays underpin nearly everything else
Domains 2 and 3
- Endocrine disease, then conception and pregnancy physiology
Domains 4 and 5
- Fertility treatment and anatomic disorders, drawing on the earlier blocks
Domain 6, then integration
- Genetics, followed by mixed review and oral-style case reasoning for the CE
For a full plan, see REI Study Guide 2026: How to Pass on Your First Attempt, and when you are ready to test yourself, try the REI practice tests to find weak spots by domain. You can also start with a timed practice set to get used to reasoning under pressure.
Where REI Subspecialists Work
REI subspecialists practice in fertility centers, academic medical centers, and hospital-affiliated reproductive medicine programs, and many combine clinical care with teaching and research. Because the work spans medicine, procedures, and laboratory collaboration, practice settings vary in how much of the ART workflow they emphasize.
If you are evaluating the career itself, REI Salary Guide 2026: Complete Earnings Analysis and Is the REI Certification Worth It? Complete ROI Analysis 2026 help you weigh the investment. For a quick orientation to the title itself, What Is A REI? and the related REI Meaning overview are good starting points.
Frequently Asked Questions
REI stands for Reproductive Endocrinology & Infertility, a subspecialty of obstetrics and gynecology focused on reproductive hormones, conception, and fertility treatment.
The American Board of Obstetrics and Gynecology (ABOG) certifies the subspecialty through a written Qualifying Examination and an oral Certifying Examination.
According to the ASRM 2025 scope-of-practice statement, the pathway is medical school, a four-year ob/gyn residency, and a three-year REI fellowship.
No. The current issuer blueprint lists six primary categories and 27 subcategories but states no percentage weights and no separate QE or CE allocation.
Yes. For fellowship graduates from 2026 onward, the thesis moves from CE eligibility to QE eligibility. Earlier graduates retain their prior requirements, so confirm your status with ABOG.