Normal Thickness Of Endometrium, Thickening Symptoms, And Causes

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The endometrium or uterine lining plays a key role in reproduction since the embryo must implant into the endometrium to initiate a pregnancy.  Endometrial thickness is a commonly measured parameter during gynecological imaging. It is an important factor for diagnosing the causes of abnormal uterine bleeding. Also, the thickness of endometrium changes every month throughout a woman’s fertile years.

Read this MomJunction post to know about the normal thickness of the endometrium, and how to recognize and deal with abnormally thickened endometrium.

What Is The Endometrium?

The endometrium is the inner lining of the uterus, where implantation of the embryo takes place. It comprises a single-layered prismatic epithelium and cell-rich connective tissue with blood vessels that surround the uterine glands. The single-layered prismatic epithelium consists of three types of cells: secretory cells, cells with cilia, and basal cells.

The endometrium undergoes various morphological and functional changes during menarche. As the level of sex hormones changes in the body during ovulation, the thickness of the endometrial lining also changes to enable the implantation of the fertilized egg. If fertilization doesn’t happen, then the endometrium lining (functional layer) sheds, leading to menstrual flow (1).

Note: The morphology and thickness of the endometrium remain constant before puberty and in menopause.

Normal Thickness Of The Endometrium

The normal thickness of endometrium varies at different stages of the menstrual cycle in premenopausal women. The normal endometrial thickness measurements are (2):

During menstruation2 – 4mm
Early proliferative phase (day: 6-14)5 – 7mm
Late proliferative/Preovulatory phaseUp to 11mm
Secretory phase (ovulation)Up to 16mm

According to a study conducted in Shanghai Jiaotong University, the rate of implantation, clinical pregnancy, and ongoing pregnancy was higher among women who had an endometrial thickness between 8-14mm. The pregnancy rate was negatively affected among the women with stripe’s thickness less than 7mm (3).

Endometrial thickness can also be used as a predictor for normal intrauterine pregnancy if there are vaginal bleeding and sonographic diagnosis of pregnancy of unknown location (4).

The following chart can give you a better idea of how the thickness of endometrium varies during the cycle.

thickness of endometrium varies

 [Read: Yoga Asanas That Boost Fertility]

What Causes Thickness of Endometrium?

Both pregnant and non-pregnant women can have an abnormally thickened endometrium due to various reasons (5).

In pregnant women, thickened endometrium could be due to:

  • Ectopic pregnancy, which can make the endometrium look thick
  • Pseudogestational sac
  • Retained products of conception
  • Heterogeneously thickened endometrium, which could be due to fluid collection
  • Heterogeneously thickened endometrium due to an intrauterine blood clot
  • Molar pregnancy, wherein the multiple small cystic spaces make the endometrium look thickened
  • Inflammation of the uterus, also called as endometritis

In non-pregnant women, it could be because of:

  • Endometrial carcinoma that gives it a thickened appearance
  • Endometrial hyperplasia or over-thickening of the endometrium
  • Endometrial polyp, or benign protrusions on the endometrial surface
  • Tamoxifen-related changes causing variable appearances of the endometrial surface
  • Endometritis

What Are The Symptoms Of An Abnormally Thick Endometrium?

The symptoms of an abnormally thick endometrium lining, also known as endometrial hyperplasia, include (6):

  • Heavier bleeding during periods
  • Longer periods than usual
  • Menstrual cycle shorter than 21 days or longer than 38 days
  • Spotting between periods

It is recommended that you visit your doctor if you are experiencing abnormal vaginal bleeding and pelvic pain.

How Is Abnormally Thick Endometrium Diagnosed?

Transvaginal ultrasound helps in identifying abnormal endometrium thickness (7).

How Does The Endometrium Look Like?

The endometrium looks like a dark line on an MRI or ultrasound scan, and it is called endometrial stripe.  Here is how the appearance and thickness of endometrial stripe change during the menstrual cycle (2):

  • Menstrual and early proliferative phase: In this phase, it appears as a thin and bright echogenic stripe that consists of a basal layer with minimal fluid.
  • Late proliferative phase: A trilaminar appearance is seen in this phase. It comprises the basal layer, middle functional layer, and the inner echogenic stripe at the center.
  • Secretory phase: Endometrium is the thickest during this phase. The stripe has fluid surrounding it and thus looks uniformly echogenic in an ultrasound.

How Is It Treated?

You should see the doctor and discuss the treatment options. Treatment will depend on the cause for thickening (6).

What Causes Thinning Of The Endometrium?

Thin endometrium results from the impairment of the normal growth of the endometrial tissues. The most common cause is menopause and it is natural. (8):

Other causes are (6):

  • Permanent damage to the basal endometrium
  • The resistance of estrogen by endometrium surface receptors
  • Decreased blood flow to the endometrium
  • Testosterone overexposure

Can Endometrial Thickness Indicate Early Pregnancy?

Endometrial thickness can indicate early pregnancy, be it normal or abnormal (ectopic). According to research reports from the University of Texas Southwestern Medical Center, Endometrial thickness between 8-40mm was noted in intrauterine pregnancies of unknown location. Among this, 70% of women had an endometrial thickness between 13-25mm. This study also shows that 70% of women with ectopic pregnancy had an endometrial thickness of less than 13mm (9).

[Read: Do Ovary Cysts Affect Pregnancy?]

Have you any experiences to share? Please share them in the comments section below.


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
1. Role and functional anatomy of the endometrium; Universities of Freiburg, Lausanne and Bern.
2. Dr Henry Knipe, Dr Yuranga Weerakkody, et al.; Endometrial thickness
3. Yu Wu, et al.; Endometrial thickness affects the outcome of in vitro fertilization and embryo transfer in normal responders after GnRH antagonist administration
4. Moschos E, Twickler DM; Endometrial thickness predicts intrauterine pregnancy in patients with pregnancy of unknown location; NCBI (2008)
5. Dr. Daniel J Bell and Radswiki et al.; Abnormally thickened endometrium (differential); (2005–2019)
6. Endometrial Hyperplasia; American College of Obstetricians and Gynecologists (2019)
7. Claudia T. Sadro; Imaging the Endometrium: A Pictorial Essay; Canadian Association of Radiologists Journal; 2016
8. Maryam Eftekhar, et al.; The thin endometrium in assisted reproductive technology: An ongoing challenge
9. E. Moschos, D. M. Twickler; Endometrial thickness predicts intrauterine pregnancy in patients with pregnancy of unknown location; International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) (2008)

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