- REI stands for Reproductive Endocrinology & Infertility, an ob/gyn subspecialty certified through the American Board of Obstetrics and Gynecology (ABOG).
- Training runs through medical school, a four-year ob/gyn residency, then a three-year REI fellowship.
- Certification has two stages: a written Qualifying Examination (QE) delivered through Pearson VUE, then an oral Certifying Examination (CE).
- The ABOG REI blueprint lists six primary categories and 27 subcategories, with no published percentage weights.
What REI Means in Medicine
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 disrupt reproductive function. Physicians who complete this training are called reproductive endocrinologists, or REI subspecialists.
On this site, the term refers only to this medical subspecialty and its board certification. If you are looking for quick definitions of the acronym itself, our short explainers on what REI stands for and REI meaning cover the vocabulary. This article goes deeper: what the field actually is, how physicians enter it, and what the certification process asks of them.
What a Reproductive Endocrinologist Does
The day-to-day work blends office-based endocrinology, procedural care, and laboratory-adjacent decision making. Unlike many ob/gyn subspecialties, REI practice often involves a close partnership with an embryology and andrology laboratory, so understanding gamete biology and assay interpretation is part of the job, not a side topic.
Clinical activities
- Infertility evaluation: diagnostic workups for female and male factors, including ovulatory function, tubal and uterine assessment, and semen analysis interpretation.
- Ovulation induction and fertility treatment: selecting and monitoring medical regimens, with attention to special considerations in individual patients.
- Assisted reproductive technology (ART): in vitro fertilization and related techniques, from stimulation through embryo transfer.
- Fertility preservation: counseling and treatment for patients facing gonadotoxic therapy or planning delayed childbearing.
- Reproductive endocrine disorders: neuroendocrine conditions, thyroid disease, polycystic ovary syndrome, and ovarian or adrenal disorders.
- Anatomic and surgical conditions: endometriosis, adenomyosis, leiomyomas, polyps, Asherman syndrome, pelvic adhesive disease, and congenital anomalies of the reproductive tract.
- Recurrent pregnancy loss and early pregnancy care: evaluation of repeated losses and management of early pregnancy problems.
- Reproductive genetics: applying genetic screening and testing to patient care.
The Training Path to REI
The ASRM 2025 scope-of-practice statement on the REI subspecialist describes the training context: medical school, then a four-year obstetrics and gynecology residency, then a three-year REI fellowship. That is a long runway, and it shapes everything about when and how a candidate approaches board certification. Eligibility details and prerequisites are covered in our guide to REI requirements, and the broader training landscape is discussed in REI training.
| Stage | Duration / Format | What it accomplishes |
|---|---|---|
| Medical school | Standard degree program | Foundation for residency entry |
| Obstetrics and gynecology residency | Four years | Core ob/gyn clinical and surgical training |
| REI fellowship | Three years | Subspecialty clinical, procedural, and research training |
| ABOG QE then CE | Written exam, then oral exam | Subspecialty board certification |
How ABOG Certifies the Subspecialty
REI board certification is administered by the American Board of Obstetrics and Gynecology. The process retains two distinct stages: a written Qualifying Examination (QE), delivered through Pearson VUE, and an oral Certifying Examination (CE). The two are separate events with separate demands, and the credential should not be conflated with either stage alone. For a plain-language overview of the credential itself, see what REI certification is and the hub page on REI certification.
What the published outcomes show
The same ABOG presentation reported 2025 REI results of a 100% first-time QE pass rate (N=55) and a 94.7% CE pass rate (N=57). The presentation's repeat-taker and overall cohort counts are internally inconsistent, so no reconciled overall pass rate should be quoted. Treat those two figures as a snapshot of one year's first-time QE and CE results rather than a prediction for any individual. A fuller discussion lives in REI pass rate, and the perception of difficulty is addressed in how hard the REI exam is.
Dates, fees, and logistics
The issuer presentation listed 2026 dates of July 20 for the subspecialty QE and April 13-17 for the CE. Those are historical 2026 dates, not an invitation to plan around, and they should not be read as upcoming booking promises. Stage-specific numeric logistics, including fees and scoring details, are not established by the common REI blueprint and remain subject to the applicable current QE or CE bulletin from ABOG. Check the bulletin before budgeting or scheduling, and see REI exam dates, REI certification cost, and REI passing score for how we frame those topics. Certified physicians also participate in continuing certification to remain certified.
The Six Clinical Domains
ABOG's REI blueprint organizes clinical content into six primary categories, containing 27 subcategories in all. The document is a common one: it does not assign separate coverage or weights to the QE and the CE, and it publishes no percentage weights. The current PDF carries no printed revision or effective date, although its URL contains 2026. We organize preparation around the same six areas, which our REI exam domains guide explores in more depth.
Domain 1: Foundational Reproductive Endocrinology
The science underneath everything else.
- Hormone structure and function
- Basic pharmacology
- Laboratory assays
Domain 2: Reproductive Endocrine Function and Disease
Physiology across life stages and the disorders that disrupt it.
- Reproductive physiology across the lifespan
- Neuroendocrine disorders 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 to 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
- Fertility treatment: special considerations
- ART techniques
- Fertility preservation
Domain 5: Anatomic Reproductive Disorders
Structural disease and its reproductive consequences.
- Pelvic adhesive disease, endometriosis, adenomyosis
- Congenital anomalies of the reproductive tract
- Asherman syndrome, leiomyomas, endometrial polyps
Domain 6: Reproductive Genetics
Genetic knowledge applied at the bedside.
- Understanding of genetic testing and screening
- Application of genetic screening and testing to patient care
Concrete Topics Candidates Must Master
Listing domains is easy; knowing what to do with them is harder. The subcategories point to the kinds of reasoning the subspecialty expects. A few patterns stand out.
Mechanism before management
Domains 1 and 2 reward candidates who can explain why a result looks the way it does. Laboratory assay interpretation, pharmacology of agents used to stimulate or suppress the reproductive axis, and the physiology of the endometrium all feed directly into treatment decisions in later domains. Weakness here tends to show up as errors everywhere else.
The lab and the clinic are one system
Gamete biology, early embryo development, ART techniques, and male infertility sit in different domains but are used together in practice. Expect to connect an embryology concept to a clinical counseling or treatment decision rather than recall it in isolation.
Anatomy meets fertility
Domain 5 covers conditions that are also common causes of infertility or pregnancy loss. Study each condition from two angles: how it is diagnosed and treated as a disease, and how it changes the reproductive prognosis.
Key Takeaway
Because ABOG publishes no percentage weights and no separate QE/CE allocation for the REI blueprint, avoid study plans that claim to know how many questions come from each domain. Cover all 27 subcategories and treat any weighting you see elsewhere as editorial opinion.
Where REI Subspecialists Work
Reproductive endocrinologists practice in a handful of recognizable settings. Fertility centers and clinics focused on ART are the most visible, often built around a shared laboratory. Academic medical centers combine clinical care with fellowship teaching and research. Hospital-affiliated reproductive medicine programs and private practices round out the picture. Specific openings and employer expectations vary, and we discuss the market in REI jobs.
If you are weighing the career itself, two related pieces address the economics without relying on unsupported figures: REI salary guide and is the REI certification worth it. For the basics, what is REI and what is a REI offer shorter introductions.
Sequencing Your Preparation by Domain
Generic study habits matter less than the order in which you work through the blueprint. Because later domains depend on earlier ones, a domain-ordered plan makes sense. Adjust the pacing to your own calendar and the applicable bulletin for the stage you are sitting.
Domain 1 and the lab
- Hormone structure and function, pharmacology, assays
- Why first: every later domain assumes this vocabulary
Domains 2 and 3
- Physiology across the lifespan, endocrine disorders, bleeding
- Gamete biology, embryo development, pregnancy endocrinology, loss
Domains 4 and 5
- Infertility evaluation, ART, preservation, male factor
- Anatomic disorders paired with their fertility implications
Domain 6 and integration
- Genetic testing and screening, applied to cases
- Mixed practice across all six domains
For a fuller framework, read our REI study guide, keep the REI cheat sheet handy for last-pass review, and test your recall with timed questions on the REI practice test site. Any question allocation across domains on our practice platform is editorial, not an official weighting.
Frequently Asked Questions
REI stands for Reproductive Endocrinology & Infertility, an obstetrics and gynecology subspecialty focused on reproductive hormones, infertility evaluation and treatment, and related reproductive disorders.
The American Board of Obstetrics and Gynecology (ABOG) certifies the subspecialty through a written Qualifying Examination followed by an oral Certifying Examination.
According to the ASRM 2025 scope-of-practice statement, training consists of medical school, a four-year obstetrics and gynecology residency, and a three-year REI fellowship.
No. The ABOG REI blueprint lists six primary categories and 27 subcategories but gives no percentage weights and no separate QE or CE allocation. Any weighting you see elsewhere is editorial.
Those numeric details are not set by the common blueprint. They appear in the applicable current QE or CE bulletin from ABOG, which you should consult before planning. Practice resources are available on the main practice test site.