The menstrual cycle is a natural process experienced by most women in their reproductive phase. The lining of the uterus, known as the endometrium, thickens in preparation for a possible pregnancy. When conception doesn’t happen, the endometrium sheds during menstruation. It is a phase when the normal size of endometrium in mm changes significantly.

The thickness of the endometrium varies throughout the life of a woman. So, what is considered normal endometrium thickness? This article will cover everything you need to know about the size of the endometrium and its importance in a woman’s reproductive health.

Normal Size of the Endometrium

Endometrium plays a crucial role during the reproductive stages in the female body. To become pregnant, women require a specific level of endometrial thickness. It is also an essential factor that works along with cervical os in pregnancy in preparation for childbirth.

If you ask about the normal size of the endometrium, it generally varies during the female lifecycle. Let’s look at them in detail below.

Premenstrual Period

It is at its smallest size in young girls who haven’t started their menstruation. The thinnest size of the endometrium is during menstruation, which can range between two and four millimeters.

Menstrual Phase

Endometrium gradually begins to thicken once the bleeding stops after menstruation. Its size can range from five to seven millimeters during the period between six and 14 days before ovulation. However, as the cycle reaches the ovulation stage, the thickness may reach 11 millimeters.

As the phase closes in on the 14th day of ovulation, when it is time to release the egg, the endometrial thickness reaches its peak. As the hormones begin their work, the thickness can go up to 16 millimeters.

During Pregnancy

Fertilization and implantation of the egg in the uterus occur when the endometrium is at its thickest. For a healthy pregnancy, the endometrium should have the right level of thickness. It should not be too thick or too thin. The perfect thickness helps with the implantation of the embryo. It also allows it to receive essential nutrients in the right quantities.

The endometrium may have a thickness of two millimeters or above during early pregnancy. However, you may not feel it as the fetus grows because of the gestational sac and placenta.

Postpartum Stage

After childbirth, the uterine line is thicker than before due to the blood clots and old tissues that stay behind. However, it returns to normal when the menstrual cycle begins again.

Menopausal and Postmenopausal Phase

During the menopausal phase, the thickness of the lines usually stays below five millimeters. Once you reach the postmenopausal stage, the thickening and thinning of the uterine line become stable.

Causes of Thin Endometrium During Pregnancy

Hormones are responsible for the thinning and thickening of the endometrium. A thin stripe usually occurs after the end of menstruation when it is smaller than seven millimeters. 

As you gradually progress in the menstrual cycle, the hormones estrogen and progesterone start their work. They aid in forming the endometrium, making it thicker and thicker. It stays thick during pregnancy and for some time after childbirth.

However, some women may experience a thin uterine lining during pregnancy. Several reasons can cause thinning of the endometrium, including the following.

  • Abnormalities in the uterus
  • Uterine problems, including structural issues
  • Prolonged use of birth controls in the past
  • Poor nourishment

How is the Thickness of Endometrium Measured?

Doctors and medical practitioners generally use ultrasound to measure the thickness of the endometrium. It is one of the standard methods used to check the health of the uterus and diagnose it for abnormalities.

However, a doctor may suggest an MRI if a person complains of extreme discomfort, pain, abnormal vaginal bleeding, and other issues. MRI may prove helpful if the uterus has abnormal positioning or if the ultrasound does not provide enough details.

When Endometrium Thickness Exceeds Normal

An unusually thick endometrium could be an indication of an underlying condition. Extreme thickness of the uterine line causes endometrial hyperplasia. It occurs when there are high numbers of cells in the uterus. 

These cells can become cancerous if left untreated and lead to endometrial cancer. It is typically seen in women in their perimenopausal or menopausal phases. General treatments include hysterectomy and progestin treatments but may vary depending on the health and age of the woman.


The normal size of the endometrium varies remarkably during a woman’s life. It can range between two and 16 millimeters depending on the reproductive stage of the person. A uterine lining that is unusually thick or extremely thin can have a significant impact on a person’s health. 

Seeking the help of a certified specialist is crucial when abnormalities in the menstrual cycle occur. Early diagnosis of symptoms can help you avoid extreme complications in the future.