On a recent morning, I saw two patients, separately, who were new to me. They both had the same complaint: they had not had a period in quite some time. The first was a woman in her late 30s with three young kids. She had been taking a low-dose combination birth control pill since the birth of her last child two years ago, and in the past six months she was not bleeding when she took the placebo pills. I reassured her that not having regular periods while taking a birth control pill is okay. She didn’t need to worry.
The second woman was also in her late 30s. She had had a progestin-eluting IUD removed about nine months prior to this visit because she and her partner were trying to conceive, but she had not had a period since removing her IUD. She mentioned that her mother and aunt had both had their last periods around age 40, and she was concerned that she might be in menopause. I was concerned too.
Two similar women with similar complaints, but my response was completely different. Knowing when to worry about an absent period (the medical term is amenorrhea) and when not to worry is confusing to many women. Let’s see if we can sort it all out.
What is a “normal” period?
Before we can talk about what is abnormal and why that abnormality is concerning, I think it is helpful to remember what normal is. A normal menstrual cycle is 21 to 35 days in length from the first day of one period to the first day of the next. A “normal” cycle length may vary from person to person, but cycle length should not vary more than 7 days from one cycle to the next.
A normal bleeding pattern is less well defined. There is no minimum number of days or quantity of bleeding that is considered too little. However, bleeding for more than 7 days is considered too long. As for volume measures, this can be subjective, but if bleeding is heavy enough that it interferes with a woman’s physical or emotional functioning, it is considered to be excessive.
Why is it important to have a regular period?
A menstrual cycle is a complex process involving multiple glands and hormones. Knowing that a woman has a normal menstrual cycle provides me with an immense amount of information from a single question. It tells me:
- She is not pregnant (or if she is, it is early)
- She is adequately nourished
- She has a functioning hypothalamus, pituitary gland, and ovaries
- She has adequate levels of estrogen
Both the regular sloughing of the uterine lining and having adequate estrogen are important for mitigating future health risks. Low estrogen during the reproductive years can increase risk for osteoporosis later in life. And frequent sloughing of the uterine lining prevents the cells that make up that lining from mutating, decreasing the risk of endometrial cancer. A regular period also helps you (and your doctor) know if and when you are ovulating, which is critical information if you are trying to conceive.
When is it okay not to have a period?
This is where things can get a little confusing. There are some times when it is completely fine not to have a period. While some of those times are obvious, others are less so.
Pregnancy and breastfeeding
Starting with the most obvious, you will not have a period when pregnant. The uterine lining is stabilized by progesterone, first from the ovary and then from the placenta, in order to support a growing fetus.
With breastfeeding, your experience may vary. Some women’s menstrual cycles are very suppressed by breastfeeding. Others will resume regular periods after just a few months. Just remember that you will ovulate before you have a period, so you should use a reliable form of contraception while breastfeeding if you don’t wish to become pregnant.
After age 45
The average age of menopause in the U.S. is 51.4 years. However, it is considered normal to experience menopause anytime between the ages of 45 and 60. Typically, the last menstrual period is preceded by at least a few years of irregular periods, but some women will have regular periods until the last menstrual period and then just stop having periods.
Hormone contraception
Several types of hormonal contraceptives, including progestin-eluting IUDs, such as Mirena, and birth control pills, can cause amenorrhea. Progestin-eluting IUDs provide contraception by keeping the uterine lining thin. Many women’s uterine lining will be so thin that they won’t experience any menstrual bleeding while they have an IUD in place.
Birth control pills can be more confusing for many women. They are designed to mimic a menstrual cycle. This is accomplished by giving progestin with or without estrogen continuously for 21 to 24 days and then suddenly withdrawing it. That is why the uterine bleeding women experience with birth control pills is called a withdrawal bleed. Women often worry if they aren’t having a withdrawal bleed, but over time, birth control pills can cause a thinner uterine lining. As a result, when the progestin is stopped, there is nothing to shed, so no withdrawal bleed occurs. Typically, regular menstrual cycles resume within a few months of stopping birth control pills as the uterine lining is allowed to build up again.
When should you worry if your periods are absent or irregular?
If you are between the ages of 18 and 45, you should have regular periods except in the situations above. It’s normal to miss a period now and again due to illness, stress, or even travel. These events trigger our pituitary to think it isn’t a good time to conceive, so the pituitary doesn’t trigger ovulation. But if you have not had a period in 90 days, it is time to see your doctor.
Irregular or absent periods are often an indication of a hormonal imbalance, such as polycystic ovary syndrome, hypothyroidism, premature ovarian insufficiency, or elevated levels of prolactin. Typically, these imbalances can (and should) be addressed even if you aren’t planning to try to conceive. Your doctor can do a few simple blood tests to investigate the cause of your irregular periods and determine if you need treatment or further evaluation.
The bottom line
- A regular menstrual cycle is defined as occurring every 21 to 35 days.
- It is normal not to have a period when you are pregnant, breastfeeding, using hormonal contraception, or are over age 45.
- If you are between the ages of 18 and 45 and have not had a period in the past 90 days, you should see your doctor for evaluation.
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Does the risk of endometrial cancer remain higher for women who don’t get their period due to use of hormonal birth control?