What Is a Reproductive Endocrinologist (REI)? How to Find a Good One

What is a reproductive endocrinologist?

A reproductive endocrinologist, or REI, is an OB/GYN who completed a further three-year fellowship in reproductive endocrinology and infertility and passed the subspecialty board exam of the American Board of Obstetrics and Gynecology (ABOG). This is the specialist who oversees egg freezing, IVF, and other fertility care, and it is the strongest credential to look for in the doctor treating you.

When you freeze your eggs, the brand on the clinic door matters less than the specific physician managing your cycle. Knowing what that physician's training actually means, and how to confirm it, is one of the most useful things you can do before choosing a clinic. Here is what the REI credential is, how it differs from a general OB/GYN, and how to verify it for any named doctor, including the ones in our directory.

REI versus a general OB/GYN

Every REI starts as an obstetrician-gynecologist. The difference is the additional subspecialty training on top.

A general OB/GYN completes medical school and a four-year residency in obstetrics and gynecology. A reproductive endocrinologist then adds a three-year fellowship focused specifically on hormones, ovarian function, and assisted reproduction, followed by a separate subspecialty certification exam. That extra training is why an REI, not a general OB/GYN, is the right person to design a stimulation protocol, read your ovarian reserve, and run a retrieval. A general gynecologist can order the initial tests and refer you, but the cycle itself belongs with the subspecialist.

What board certification actually signals

Board certification in reproductive endocrinology and infertility comes from ABOG and confirms the doctor met a defined standard of training and passed the exam. Crucially, it attaches to the individual physician, not to the clinic.

That distinction matters more than it sounds. A clinic can market itself around a well-known name who has since retired or moved, while your actual care is handled by someone else. So the credential you want to confirm is not "this is a good clinic" but "this specific doctor, the one who will treat me, is a board-certified REI and is currently on staff here." Our directory tracks exactly that: whether each named doctor is verified and currently practising.

How to find and verify a good REI

Once you know what to look for, verification is straightforward.

• Get the name. Ask which doctor will manage your cycle. A clinic that will only offer "our team" is giving you less to verify.
• Confirm board certification. Check that the doctor holds ABOG subspecialty certification in reproductive endocrinology and infertility, not only general OB/GYN certification.
• Confirm they are current. Make sure the named doctor still practises at that clinic now, not in an old bio or a press mention.
• Look for society membership. Active involvement with ASRM or SART is a reasonable secondary signal of engagement with current standards.
• Match experience to your case. If you have PCOS, endometriosis, or low ovarian reserve, ask how often the doctor treats patients like you.

You can browse the named reproductive endocrinologists behind each clinic on our doctors page, which flags who is verified, or start from the clinic directory and work to the doctor.

Why the doctor matters as much as the clinic

Egg freezing outcomes depend on judgment: how your protocol is tailored, how your monitoring is read, how the retrieval is timed, and how honestly you are counselled about your real odds. Those are functions of the doctor and the embryology lab, not the marketing. A named, board-certified REI you have personally verified is the single clearest signal that the person making those calls is qualified to make them.

Understanding what a reproductive endocrinologist is turns a vague search for a "good clinic" into a specific, checkable question about the person who will actually treat you. Confirm the name, confirm the ABOG certification, confirm they are still there, and you have done more due diligence than most patients ever do. From there, our guide to choosing a clinic covers the rest.