All About the Endometrial Lining

The endometrium is the inner lining of the uterus. It plays an important role in women's reproductive health. The uterine lining changes throughout the month, along with the menstrual cycle, in response to your body's reproductive hormones, estrogen and progesterone.

Sometimes, the endometrial lining is abnormally thick or thin, which can impact your ability to become pregnant and can cause irregular bleeding. Understanding this changing organ can help you take steps to ensure that you have a healthy endometrial lining.

This article explains the function of the endometrial lining during menstruation, conception and pregnancy, and menopause. It also discusses normal vs. abnormal endometrial lining thickness, along with conditions that can affect it.

Endometrial Lining Function

The endometrial lining functions primarily during a woman's reproductive years. This inner lining of the uterus begins to thicken to prepare for an embryo to implant, or for pregnancy to occur. If pregnancy occurs, the lining helps to maintain the pregnancy. If pregnancy does not occur, the lining sheds (you get your period), and the process begins again for the following cycle.1

During Menstruation

When you do not become pregnant after ovulation, the estrogen and progesterone levels in your body drop rapidly, which initiates the start of your menstrual cycle. At the start of your menstrual cycle, your body discards the buildup of your endometrial lining, a mix of blood and tissues, which passes through the cervix and exits your body through the vagina. This process can take several days and is referred to as your period.3

During Conception and Pregnancy

Hormone levels in the body begin to rise again after your period, which initiates changes to the endometrial lining. During the follicular or proliferative phase, estrogen signals for the cells lining the endometrium to multiply and for blood vessels to grow to supply the new layers of cells. At the end of the follicular phase, ovulation occurs (an egg is released from one of the ovaries).4

Following ovulation, the secretory phase begins, initiated by an increase of the hormone progesterone. Specialized glands in the endometrium begin to secrete nutrients that will nourish an embryo. This thickening of the lining and supply of blood and nutrients prepares the uterine lining for implantation, when a fertilized embryo attaches to the uterine wall. During pregnancy, the endometrial lining continues to thicken to support the growing baby.4

Around Menopause

Menopause is the period of time 12 consecutive months after a person's last menstrual cycle. This occurs with age (typically between ages 45 and 55), but can also be triggered by a hysterectomy (surgery to remove the uterus), surgery that removes the ovaries, or medication that causes the ovaries to stop producing hormones.

Because there is no cyclical rise and fall of the reproductive hormones estrogen and progesterone during menopause, the uterine lining is relatively stable during this time.5

Is There a “Normal” Endometrial Thickness?

"Normal" endometrial thickness varies from person to person, as well as throughout the person's lifecycle. What is normal for an individual will change during childhood, throughout menstruation, during the reproductive years, and after menopause. Health conditions and medical treatments such as hormone replacement therapy can also affect the thickness of the endometrial lining.

Endometrial thickness is measured in millimeters using an ultrasound or magnetic resonance imaging (MRI). "Normal" endometrial thickness measurements are as follows during the various phases:6

• Menstruation: 1–4 millimeters
• Proliferative Phase: 12-13 millimeters
• Secretory Phase: 16–18 millimeters
• Menopause: 3 millimeters or less

Note that these ranges are being called into question because, in Black people, there are differences in the prevalence of fibroids and non-endometrioid endometrial cancer, which can affect the endometrial thickness and lead to missed or delayed diagnoses.7

What Are the Symptoms of a Thick Uterine Lining?

Possible symptoms of a thick uterine lining include:8

• Menstrual periods that are heavier than normal
• Menstrual periods that are longer than normal
• Bleeding between menstrual periods
• Menstrual cycles that are shorter than 21 days
• Menstrual-like bleeding after menopause
• Anemia (due to heavy bleeding)
  

Health Conditions That Affect Size

There are various health conditions that affect your endometrial lining, including:

• Endometriosis: With this condition, the endometrium grows outside the uterus. This can cause inflammation, irritation, and swelling and can lead to scarring and damage of the tissue surrounding the uterus.4
• Ovarian tumors, uterine cancer, and fibroids: Any abnormal growth of cells in the uterus, such as cancer or fibroids, can impact the size of the lining of the uterus by blocking blood flow or changing the shape of the uterus.9
• Hyperplasia: Hyperplasia is caused by a hormonal imbalance of estrogen and progesterone. Too much estrogen can overstimulate the endometrial lining to become overly thick.4
• Obesity: Fat tissue is responsible for the production of hormones, including estrogen. Additional body fat can increase your estrogen production causing overstimulation of the endometrial lining, and may increase your risk for endometrial cancer.10
• Medications and treatments: Medications that act on hormones or hormone receptors, such as tamoxifen (often used in cancer treatment), may increase your risk of abnormal growth in the endometrial lining, including endometrial polyps, hyperplasia, and uterine cancer.11 Hormone replacement therapy (HRT) can also cause the endometrial lining to vary because of the increase in estrogen.12
• Type II diabetes: High insulin levels in diabetes lower levels of sex hormone-binding globulin (SHBG). This hormone helps regulate the body's use of estrogen. Thus, if there is too little SHGB, excessive estrogen can cause the uterine lining to grow and thicken.13
• Polycystic ovarian syndrome (PCOS): In people with PCOS, uncontrolled levels of estrogen can cause the endometrium to thicken abnormally. Hormone imbalances in PCOS can also prevent ovulation. As a result, the uterine lining may not shed each month as it normally should.14
  

What You Can Do

A thickened endometrial lining is often an incidental finding.. But some conditions in which it may be found can cause menstrual abnormalities. If it is too thin, it may prevent you from getting pregnant and it may cause irregular periods.

However, there are some steps you can take to manage symptoms and conditions related to your endometrial lining.

Lifestyle Changes

A healthy, well-balanced diet can be beneficial in fighting pain and inflammation, improving blood flow, and supporting hormonal balance. Overall, healthy diets are linked to better fertility and higher live birth rates, while poor-quality diets are linked to such endometrial conditions as endometriosis and endometrial cancer. A diet that supports healthy endometrial lining includes:15

• A variety of plant foods rich in antioxidants, vitamins, and minerals (dark, leafy greens, beans, cabbage, broccoli)
• Whole grains and fiber (brown rice, oats, bran, enriched whole grain product)16
• Omega-3 essential fatty acids (oily fish, flaxseed)
• Healthful fats (olive oil, nuts, seeds)
• Lean meats (grass-fed beef, poultry, fish)
• Spices that increase blood flow (ginger, saffron, turmeric, cinnamon, garlic)

Reducing alcohol, caffeine, and foods high in sugar may also be beneficial. These substances are inflammatory and reduce blood flow.

Exercise may be beneficial in increasing blood flow to the uterine lining.

Natural Treatments

Studies have revealed that supplements may help improve blood flow to the uterus and may support a healthy endometrium if you are trying to achieve pregnancy and have have implantation failure. These include L-arginine and vitamin E.17

Many studies cite acupuncture as a commonly used treatment to support women who are trying to get pregnant. One study has shown that acupuncture helped increase the success rate of IVF in study participants. It did not show, however, whether results were due to an increase in blood flow to the uterus, a reduction of stress and anxiety, or a change in immune function.18

Medical Treatments

Hormones may be used to moderate the thickness of the endometrial lining. Progesterone may be used in hyperplasia to decrease endometrial thickness. Estrogen may be used to thicken the endometrial lining if it is too thin.19

If you do not want any future pregnancies, surgery such as a hysterectomy may be an option to discuss with your doctor. Surgery may also be considered if the tissue impacting endometrial thickness is structural, such as a fibroid or polyp. In these cases, surgery may be used to remove the obstruction.20

When to See a Healthcare Provider

If your menstrual periods last longer, seem heavier, or are more painful than what you're used to, call your healthcare provider. If you are post-menopause and bleeding at all, see a healthcare provider as soon as you can.

You should also let your provider know if you are experiencing:

• Signs of anemia, such as weakness or dizziness
• Spotting between periods
• Pain during sex or unusual pain in your low back or pelvis
• Infertility or difficulty getting pregnant
• Abnormal vaginal discharge
• Unexplained weight loss
• Difficulty urinating
• Abdominal pain

While it is normal to feel mild pain during or before your menstrual period, it is not normal for the pain to stop you from doing your normal daily activities. Don't hesitate to contact a healthcare provider or gynecologist if something seems off.

Summary

The endometrium is the inner lining of the uterus. The uterine lining changes throughout the month, along with the menstrual cycle. During a woman's reproductive years, the lining thickens to prepare for pregnancy to occur.

"Normal" endometrial thickness varies from person to person and fluctuates over time. What is normal for one person will change during childhood, throughout menstruation, during the reproductive years, and after menopause. Various health conditions can also affect the endometrial lining. Certain lifestyle factors, such as consuming a healthy, well-balanced diet, can help improve blood flow and decrease pain.