Thick lining around uterus

Menstrual Cycle and Periods

Quick look at the menstrual cycle and periods

A woman’s period, or menstruation, is when the lining of the womb sheds, along with blood, exiting through the vagina. When these periods occur regularly, this is referred to as the menstrual cycle.

A period happens if egg fertilization does not occur. This menstruation usually lasts 3-5 days. The average menstrual cycle lasts 28 days, but can range from 21-45 days depending on the woman’s age.

The cause of the monthly period is related to the changes a woman’s body undergoes in ovulating an egg roughly once a month for possible reproduction.

Various treatment options are available for the many women experiencing abnormal (heavy, irregular or painful) periods and other issues.

Why women have periods & what happens to her body

A woman’s period is related to the changes her body undergoes in ovulating an egg for possible fertilization. The period, or menstruation, is when she sheds the lining of the uterus and other blood after her ovulated egg is not fertilized. The uterine lining is no longer needed for an embryo to implant to for pregnancy. When the periods occur with regularity, this is called the menstrual cycle.

Women’s ovaries are in the lower part of the abdomen located on either side of the uterus. The ovaries start to produce hormones around puberty, which causes changes to the lining of the uterus (womb). The period, which is the shedding of the lining, is known as menstruation. For most women, the menstrual period occurs once a month and lasts from three to five days.

The menstrual cycle provides the hormones estrogen and progesterone, which rise and fall during the month to control the cycle. The average menstrual cycle lasts 28 days. But in adults it can range anywhere from 21 to 35 days, and in teens can range from 21 to 45 days.

Estrogen levels begin to rise in the first half of the cycle, which prompts the lining of the uterus to grow and thicken. This lining nourishes the embryo if a pregnancy occurs. During this same time frame, an egg in one of the ovaries begins to mature.

About half way through the menstrual cycle ovulation takes place. Ovulation is when the egg leaves the ovary. The egg will then begin traveling through the fallopian tube toward the uterus. During this time, hormone levels continue to rise and help prepare the wall of the uterus for pregnancy. Women are most likely to get pregnant during the three days prior to, or on the day of ovulation.

Pregnancy occurs if the egg is fertilized by a man’s sperm and the resulting embryo attaches to the uterine wall. If the egg is not fertilized, hormone levels drop, which signals for the next menstrual cycle to begin and the egg will be shed with the uterine lining in the next period.

Is my period normal?

Everyone’s period is different. The amount of blood, called the menstrual flow, could be light, moderate or heavy. The length of the period also varies in women, with most periods lasting between three and five days. As a woman matures, her cycle tends to shorten and become more regular.

In the United States, the average age a girl starts her period is 12, but it can start as early as 8 or as late as 15. The first period tends to start about two years after a girl’s breasts begin to develop. If a girl has not started her period by age 15 or two to three years since breast growth started, she should make an appointment with her healthcare provider.

A woman usually has her periods until menopause, which occurs between the ages of 45 and 55. During menopause a woman stops ovulating (releasing eggs) and can no longer get pregnant.

Problems with periods

The menstrual cycle and a woman’s period can have a range of problems including, pain, irregularity and heavy bleeding. Some common problems women experience with their periods follow.


Lack of a menstrual period. Amenorrhea describes the absence of a period in young women who have not started their period by age 15, or in women who have not had their period for 90 days. This can be caused by eating disorders, excessive exercising, stress or a medical condition. If at any point a woman does not have her period for 90 days, she should see her doctor to check for pregnancy, early menopause or other possible health problems.


Painful periods, including severe cramps. Most teens with dysmenorrhea do not have a serious disease, rather their body is producing too much of a chemical called prostaglandin that causes menstrual cramps. In older women this pain can be caused by various conditions such as endometriosis or uterine fibroids. Women who experience painful periods should speak to their OB-GYN about their symptoms.

Abnormal uterine bleeding (AUB)

Bleeding that is irregular for a woman’s normal menstrual period. AUB can include:

  • Bleeding between periods
  • Bleeding for more days than normal
  • Bleeding after sex
  • Bleeding after menopause
  • Heavy bleeding
  • Spotting anytime in the menstrual cycle.

Abnormal bleeding can be caused by many different issues. When experiencing AUB, it is important for women to see their doctor to begin checking for causes. Some causes are not serious and are easy to treat, but others could be more serious.

Heavy or prolonged bleeding

One of the most common forms of AUB. A woman’s period is considered heavy if there is enough blood to soak a tampon or pad every hour for several consecutive hours. Other symptoms can include passing blood clots larger than a quarter during menstruation, needing to change pads or tampons during the night, or a period that lasts longer than seven days.

If a woman experiences heavy menstrual bleeding, it is important that she see an OB-GYN. Evaluation for irregular, painful or heavy periods might include:

  • Consultation with an OB-GYN to discuss symptoms
  • Pelvic ultrasound to evaluate for structural problems with the uterus
  • Blood tests.

Examples of treatment options for irregular, painful and heavy periods

Hormone therapy

Hormone therapy is often an initial option for treating period issues. Hormones found in birth control pills or IUDs (intrauterine devices) stabilize the lining of the uterus, regulate menstrual cycles or correct hormonal imbalances. They can also reduce pelvic pain, cramping or other symptoms accompanying the menstrual cycle.


Nonsteroidal anti-inflammatory medications (Advil, Motrin, Aleve, ibuprofen) minimize production of prostaglandins, the chemical that causes cramps.

Lysteda (tranexamic acid) is a nonhormonal medication that promotes blood clotting and may be recommended for women experiencing heavy bleeding.


Surgery is recommended when anatomical problems lead to irregular periods, particularly in women who want to have children. It may also be done to remove severe scar tissue (adhesions) in the reproductive tract. In more severe cases, surgery may be used to remove a woman’s uterus to eliminate periods altogether.

Surgeries for period problems may include:

  • D&C (dilation and curettage) – a brief surgical procedure that dilates the cervix and scrapes the lining of the uterus.
  • Hysteroscopy – a minimally invasive procedure that uses a hysteroscope to allow the doctor to see inside the uterus and remove masses from its cavity.
  • Endometrial ablation – a procedure destroying the endometrium (lining of the uterus) to lighten or stop a woman’s period. It is not recommended for women who wish to become pregnant in the future.
  • Hysterectomy – the surgical removal of the uterus and cervix.

About periods

In most women, the ‘menstrual cycle’ happens over 28 days, starting with the first day of your period. With each cycle your body prepares the lining of your uterus to create the ideal environment for a possible pregnancy.

Why do we have periods?

Your menstrual cycle is the time between one period and the next. Every month there is a complex interaction between the pituitary gland in the brain, the ovaries and the uterus (or womb). Messages and hormones are being passed around the body to prepare it for a possible pregnancy. An egg is produced, the lining of the uterus thickens up, hormones prepare the vagina and the cervix to accept and support sperm. When pregnancy doesn’t occur, the egg is absorbed back into the body and the thick lining in the uterus is shed, this is your period. Then the cycle begins all over again.

  • Day one of your cycle is the first day of your period. This is when your uterus starts shedding the lining it has built up over the last 28 days.
  • After your period is over, the lining of your uterus starts to build up again to become a thick and spongy ‘nest’ in preparation for a possible pregnancy.
  • On day 14 (for most women), one of your ovaries will release an egg, which will make its way through a fallopian tube and will eventually make its way to your uterus (called ovulation).
  • On day 28 (for most women), if you have not become pregnant, the lining of your uterus starts to shed. This is your period. The blood you lose during your period is the lining of your uterus.

The menstural cycle

If you have sex during a cycle, and your egg meets a sperm, you can become pregnant. When you’re pregnant, you don’t get your period.

Is a cycle always 28 days?

The average cycle is 28 days but, for some women, it is as short as 21 days, for others it is as long as 35 days. When you first start having periods, it can also take a while before your periods develop a regular pattern. Your cycle also changes as you get older.

Your menstruation cycle (and period) stops temporarily when you are pregnant. Breastfeeding also affects your cycle. At the end of menopause, your cycle stops permanently.

What does a period feel like?

Some women will have pain in their belly (the lower abdomen). This can be a crampy pain or just a mild ache. You may have lower backache on its own or with the pain in your belly. The pain can often be stronger on the first day or two of your period and will vary in strength and severity from one women to another. Some women also have a headache or feel very tired just before their period arrives or on the first day. Mood changes, teariness and easily losing your temper can sometimes be an indicator that you are getting your period, this is referred to as premenstrual syndrome (PMS) or premenstrual tension (PMT). For some women this can be so overwhelming that they are unable to go about their normal lives. Any symptoms that you find hard to manage should be investigated with your GP.

Many women have no symptoms at all. It is not uncommon for women to notice that they have their period only after they have gone to the toilet and found that there is blood on their underpants or on their toilet paper.

Even without overwhelming symptoms, some women still find it comforting to simply take time out when they get their period, and cuddle up with a hot water bottle.

Adolescent girls and women can both experience skin changes and pimples with their periods.

What to do when you get your period

Before you start getting periods it is good to be prepared for when it eventually comes. Hopefully you will have an opportunity to talk with your mother or sister or someone else in your family who can help you to prepare. Meanwhile here are some tips for when you do start bleeding.

  • Use sanitary products like a pad, tampon or panty liner to absorb the bleeding. Pads and liners are longs strips of cotton that you stick to your underwear. Tampons are thin cylinders of dense cotton attached to a string that you put inside your vagina. Pads, liners and tampons come in different shapes and sizes but all of them need to be changed every four to six hours to stop leakage. You can use a tampon whenever you want, you don’t have to wait until you start having sex before a tampon will go in. It may be a little hard to get it in to begin with, but you will get used to it very quickly.
  • Keep a ‘period kit’ somewhere handy. This is because you might get your period unexpectedly or forget it’s due. Keeping some painkillers, sanitary products and a spare pair of underpants in your bag, at school or at work can be a lifesaver.
  • Enjoy life as much as possible. It’s safe and often possible to do all the things you would normally do. It’s also okay to have sex when you have your period, but if you’re using a tampon you’ll need to take it out first.

If you have period pain you can take painkillers that you can buy over the counter at the chemist. If your pain isn’t relieved with regular painkillers, visit your GP (your local doctor).

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The Women’s does not accept any liability to any person for the information or advice (or use of such information or advice) which is provided on the Website or incorporated into it by reference. The Women’s provide this information on the understanding that all persons accessing it take responsibility for assessing its relevance and accuracy. Women are encouraged to discuss their health needs with a health practitioner. If you have concerns about your health, you should seek advice from your health care provider or if you require urgent care you should go to the nearest Emergency Dept.

US Pharm. 2011;36(9):17-18.

Uterine-Lining Tissue That Grows Outside the Uterus

The interior of the uterus is lined with a mucous membrane known as the endometrium. Each month, estrogen and progesterone stimulate the endometrial cells to grow and thicken in order to prepare for possible implantation of a fertilized egg. If a fertilized egg is not implanted during a monthly cycle, the endometrial lining breaks down and is shed during menstruation.

Endometrial tissue sometimes develops in other areas of the body, resulting in a condition known as endometriosis. This tissue may occur in the ovaries, fallopian tubes, bladder, rectum, bowel, or pelvic or abdominal cavity. Even though the tissue is located outside the uterus, it responds to monthly hormonal changes by breaking down and bleeding as if it were part of the shedding endometrium. Swelling and the eventual breakdown and bleeding of endometriotic tissue can cause pelvic or lower back pain, bleeding into surrounding tissue, and scarring. Many women with endometriosis experience symptoms, but sometimes the disease is asymptomatic. Damage caused by endometriosis cannot be reversed and may lead to scarring, cyst formation, or infertility.

Endometriosis treatment depends upon the patient’s age, extent of pelvic involvement, symptom severity, and desire for pregnancy. Mild pain sometimes can be controlled by nonsteroidal anti-inflammatory drugs (e.g., ibuprofen, naproxen). Monthly cycles may be manipulated by using estrogen and progesterone to control endometrial growth, breakdown, and bleeding. Gonadotropins can shut down the ovaries’ production of estrogen, but they have side effects. If pregnancy is desired or if medications do not relieve symptoms, surgery to remove the endometrial tissue and surrounding scar tissue is an effective alternative. Another option is partial or total hysterectomy, which cures endometriosis in most patients.

Pain Severity Does Not Indicate the Severity of Disease

Endometriosis, a condition in which the tissue lining the inside of the uterus also grows elsewhere in the body, is usually diagnosed when a woman is in her mid-20s to mid-40s, but probably begins much earlier. Women who have not had children or who have a close relative with endometriosis are at greater risk, as are women whose menstrual cycles are less than 28 days or whose periods last longer than 7 days.

It is unclear why endometriosis occurs or why endometrial cells develop outside the uterine lining. During menstruation, these cells may be transported backward through the fallopian tubes and into the pelvic or abdominal cavity. Another theory is that endometrial cells enter the bloodstream or lymph system during normal endometrial shedding and are transported to other parts of the body.

Symptoms and Diagnosis

Symptoms of endometriosis do not always occur, even with extensive disease. The severity of symptoms such as pain is not necessarily related to the severity of the condition. Mild endometriosis may cause serious pain in one woman, while in another significant disease may go unnoticed until a physician is consulted for infertility. Most women with endometriosis have some degree of pelvic pain. Pain may occur just before menstruation begins, during menstrual bleeding, while having a bowel movement or urinating, or during sexual intercourse. The pain is caused by endometrial-tissue breakdown and scar-tissue formation in the area. In many cases, the bleeding and scarring cause permanent adhesions (scar tissue attaching two separate organs) in the pelvic region. Sometimes, an endometrioma (cyst made of endometrial tissue) forms on the ovary.

Endometriosis is diagnosed by symptom history, pelvic examination, transvaginal ultrasound, and/or pelvic laparoscopy. In laparoscopy, a small tube with a lighted camera is inserted into the pelvic cavity; during the procedure, a piece of tissue may be biopsied to confirm diagnosis, or endometrial tissue may be removed.


Treatment is based on symptom severity, disease involvement, and desire for pregnancy. Nonsteroidal anti-inflammatory drugs may be used for mild pain, but they do not treat the cause of endometriosis. Hormone-containing medications can ease the pain and control the cyclic swelling, bleeding, and scarring of endometrial tissue, but they have side effects and do not reverse existing scarring.

Using birth control pills continuously for up to 9 months and then stopping them briefly to permit menstruation can relieve symptoms by creating an artificial pregnancy state. In fact, many pregnant women experience relief from endometrial pain because of the hormonal shift. Side effects of this therapy include nausea, breast tenderness, and spotting.

Gonadotropin-releasing hormone (GnRH) may be used to shut down the ovaries’ production of estrogen, similar to what occurs in menopause. GnRH causes menopausal symptoms such as hot flashes and bone-density loss. Progestin, which stops menstruation by working against estrogen’s effects, also may be used, but it may cause moodiness, weight gain, and bloating.

Surgical removal of endometrial tissue and surrounding scar tissue typically is reserved for severe cases that do not respond to hormone therapy or for infertile patients wishing to conceive. Endometriosis is permanently cured in about 50% of patients; in the rest, symptoms may return within a year.

The most permanent treatment is hysterectomy (removal of the uterus). The ovaries may be removed as well, further reducing the chance of symptoms returning. The patient will no longer menstruate or be able to conceive, and endometriosis is highly unlikely to return.

Abnormally thickened endometrium (differential)

Abnormally thickened endometrium on imaging may occur for a number of reasons which may be categorized based on whether or not they are related to pregnancy. Etiologies may also be classified based on whether the patient is premenopausal or postmenopausal.

On this page:


  • Differential diagnosis
  • Practical points
  • See also


  • Cases and figures

Differential diagnosis

  • early pregnancy: prior to sac being visualized (<5 weeks of gestation)
  • ectopic pregnancy: thickened endometrium and sometimes fluid collection or pseudogestational sac can be associated
  • retained products of conception
    • heterogeneously thickened endometrium, with increased vascularity
    • may be fluid collection(s)
    • findings are usually associated with an enlarged uterus
  • intrauterine blood clot: heterogeneous endometrium with no vascularity
  • molar pregnancy: thickened with multiple small cystic spaces
  • recent gestational state (delivery)
    • endometritis
  • endometrial carcinoma: variable appearance
  • endometrial hyperplasia: usually uniformly hyperechoic and tends to be diffuse. Can be a differential diagnosis of many conditions i.e. PCOS
  • endometrial polyp: usually hyperechoic, often focal, look for vascular stalk
  • Tamoxifen-related endometrial changes: variable appearances
  • hormone replacement therapy (HRT): in postmenopausal female
  • endometritis: prominent hyperechoic endometrium +/- fluid and debris
  • adhesions: irregular echogenic areas with focal thickening
  • obstructed outlet
  • ovarian tumors associated with endometrial thickening
    • endometrioid carcinoma of the ovary
    • granulosa cell ovarian cancer

Practical points

  • endometrial thickness in the secretory phase (days 14-28) may normally be up to 12-16 mm (see: endometrial thickness)
    • non-emergent ultrasounds are optimally evaluated at day 5-10 of the menstrual cycle to reduce the wide variation in endometrial thickness
  • the thickest portion of the endometrium should be measured
  • if there is fluid in the uterine cavity, it should be excluded from the measurement, which would be the sum of the two sagittal plane thicknesses
  • ~10% of endometrial carcinoma occurs in premenopausal women
  • endometrial thickness
  • abnormally thickened myometrium
  • uterine enlargement

At what endometrial thickness should biopsy be performed in postmenopausal women without vaginal bleeding?

With no consensus regarding the normal endometrial thickness in postmenopausal women without vaginal bleeding, there are no guidelines for clinicians to follow on when to biopsy, if at all, in an older patient presenting with pelvic pain but no bleeding.

To determine at what endometrial thickness biopsy would be optimal, Michelle Louie, MD, and colleagues from Magee Women’s Hospital in Pittsburgh, Pennsylvania, performed a retrospective cohort analysis of postmenopausal women aged 50 or older who underwent transvaginal ultrasound (TVUS) for indications other than vaginal bleeding. They presented their findings in an abstract at the 43rd AAGL Global Congress in Vancouver, Canada.

Details of the study

Patients were included if they had an endometrial lining of 4 mm or greater and excluded if they had a history of tamoxifen use, hormone replacement, endometrial ablation, hereditary cancer syndrome, or no available pathology results.

Of 462 biopsies, 435 (94.2%) had benign pathology, nine (2.0%) had carcinoma, and seven (1.5%) had atypical hyperplasia.

Under 14 mm, the risk of hyperplasia was low, the authors found, at 0.08%. Below 15 mm, the risk of cancer was 0.06%.

They found no significant associations between endometrial lining TVUS appearance, age, parity, body mass index, diabetes, hypertension, hyperlipidemia, and carcinoma or atypical hyperplasia.

When biopsy might not be necessary

Therefore, regardless of conventional risk factors for endometrial cancer, if a postmenopausal woman reports pelvic pain without vaginal bleeding, and is found to have a thickened endometrial lining of less than 14 mm on TVUS, biopsy might not be warranted, conclude the study authors.

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