Your Endometrial Lining: Why It Matters So Much

If you have gone through any part of the IVF process, you’ve probably had your endometrial lining measured during an ultrasound. Your endometrial lining plays a critical role in the success of your IVF cycle; it’s where your embryo will hopefully implant and grow. 

We know there are plenty of questions when it comes to interpreting these results, so below, we’ve answered some of them for you. Whether you’re worried your lining is too thick, too thin, or just not looking optimal, we’ve got you covered.

A Normal Lining

First, a quick disclaimer: no two uterine linings are exactly the same. Each person's uterus is unique, and even your own lining will change throughout your menstrual cycle.

• During your period, the lining is at its thinnest—typically around 2–4 mm—as your uterine lining is shedding. 

• In the follicular phase, it begins to rebuild, thickening to about 7–10 mm under ideal circumstances.

• At ovulation, the lining reaches its peak thickness, ideally setting the stage for a successful implantation.

So what’s ideal for an embryo transfer?
Generally, a lining between 7–14 millimeters is considered optimal for implantation.

A Lining That’s Too Thin

An endometrial lining of less than 6-7mm is generally considered too thin for a successful embryo transfer. That’s not to say that embryos don’t implant with thinner linings—but ideally, there needs to be adequate “soil” for an embryo to find fertile ground. 

There are several possible reasons for a thin lining, including low estrogen levels, smoking, previous uterine surgeries, or chronic endometritis.

The good news? There are ways to help. There are many protocols for developing a thicker lining, and a thorough review of your past cycles and when you had your best uterine lining can give clues as to the next indicated step. Some women respond better to a “natural” or “modified natural” cycle for a frozen embryo transfer preparation. If the culprit is chronic endometritis, a course of antibiotics and a test of cure endometrial biopsy can be helpful. Some women need hysteroscopic surgery for intrauterine scar tissue if that seems to be the etiology. Other people have tried adjuncts such as vitamin E, baby aspirin, sildenafil, PRP, and/or neupogen washes, however the data  are still limited.. The good news is that frozen embryos are safe in the incubator and do not age with you. Although a delay can feel like an enormous gut punch, it’s best to wait until more ideal conditions to proceed with a transfer. 

What About a Lining That’s Too Thick?

A thick endometrium is usually defined as a lining over 14 millimeters. While it might seem like thicker is better, an overly thick lining can sometimes indicate  polyps, hyperplasia, or hormonal imbalance—all of which may reduce implantation success.

If your REI finds your lining to be too thick, they may suggest a sonohysterogram and/or an endometrial biopsy. This brief procedure can be uncomfortable, so ask about options for pain management ahead of time. Our favorite is a valium about 30 minutes prior to the procedure, however you would need a driver and to sign any consents ahead of time. 

If there is a diagnosis, your REI can help get your lining back on track, either with a polypectomy, or even a simple course of progesterone to shed the lining and restart again, sometimes with a shorter duration of estradiol. Although even still, sometimes there is no pathological diagnosis, and some women just grow a thicker lining. Most of us REI’s believe that the qualitative appearance of the endometrium is just as important, if not more important, than the quantitative thickness,  however we definitely need more data in this regard. 

Delaying Your Cycle

If your lining is either too thick or too thin to move forward, your REI may recommend delaying your embryo transfer cycle. We know this can be incredibly difficult—especially after waiting so long.

This is where mindset becomes essential. It helps to trust that your REI is helping you make the best decisions for your long-term success. They want nothing more than for you to get pregnant—and stay pregnant.

We know waiting is hard, and if you’re struggling, Love & Science Fertility is here to support you. Dr. Erica Bove has extensive experience with uterine lining issues, as well as how to pass the time (and even thrive) while you wait. Additionally, she is the only REI physician coach in the world. Hundreds of physician patients have allowed her to guide them as they crossed the bridge to parenthood, and her method works.

Click here to learn more about Dr. Bove’s method and to get started.