If you missed your period, yet still get a negative pregnancy test, you may be wondering what this means—especially if you have been trying to conceive. But before worrying, it's important to first recognize that it is possible to get a false negative result. 

Most of the time, false negatives occur when you take a pregnancy test too early in your cycle, or if you don't closely follow the manufacturer’s instructions. Fluctuations in your menstrual cycle also could be at the root of a false negative.

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“Not all women have regular, monthly periods,” explains Julia Arnold VanRooyen, M.D., an OB-GYN and board-certified gynecologic surgeon. “It is considered normal to have periods ranging in frequency anywhere from every 21 to 35 days, and periods can also vary from month to month.”

Aside from these common fluctuations in your cycle and taking the test too early, there also are other potential causes for missing a period. Keep reading to find out why you may have missed your period, how accurate pregnancy tests are, and when to call a health care provider.

Reasons Your Period Might Be Late

When it comes to missing a period, there are a number of reasons you could be late—from hormone levels or stress to excessive exercise or significant weight changes.

In fact, the most likely causes of a missed menstrual period in people of childbearing age are pregnancy, stress, or side effects from birth control.1 But there could be other factors at play as well. Here's a closer look at some of the more common reasons for missing a period that have nothing to do with being pregnant.

Lifestyle Factors 

Are you exercising excessively, breastfeeding a little one, or dealing with a lot of stress? Any of these factors can impact your period and cause you to be late—or even miss it altogether, according to Dr. VanRooyen. This is largely due to the impact these situations have on your estrogen levels.2

“Estrogen—the hormone that builds up the lining of the uterus which is then shed as a menstrual period—is made predominantly in the ovaries, but also the adrenal glands and in fat cells,” explains Dr. VanRooyen. “So large weight gains or losses can lead to changes in the amount of estrogen in the body.”

Meanwhile, stress activates the adrenal glands to produce other hormones, like cortisol. This can also suppress the secretion of estrogen, she says. “Even excessive exercise leading to very low amounts of body fat can result in decreased amounts of estrogen.”

While you are breastfeeding, it's also possible to miss a period—especially if you're breastfeeding exclusively. That's because the milk-producing hormone, prolactin, temporarily blocks estrogen production.3 Even so, most health care providers recommend using some form of birth control while breastfeeding if you do not wish to get pregnant.

Medications

Many different types of medications can lead to delayed or absent periods. For instance, hormonal forms of contraception—like oral contraceptive pills, patches, vaginal rings, and certain IUDs—can all affect periods, says Dr. VanRooyen. 

“Many women have much lighter periods or may stop having periods entirely while using hormonal contraception,” she adds. “This is normal and not dangerous or worrisome. Other medicines that can lead to changes in menstrual cycles include steroids, anti-coagulants (blood thinners), and certain chemotherapies.”4

Fluctuating Hormones

Changing hormone levels in your body can also lead to missed or absent periods. For instance, if you have an over-active thyroid (hyperthyroidism) or an under-active thyroid (hypothyroidism), this can cause menstrual irregularities.2

Likewise, your pituitary gland regulates the production of hormones that affect many of your body’s functions, including the reproductive cycle. A tumor on your pituitary gland can interfere with menstruation and cause you to miss your period or experience other irregularities.2 Fortunately, these tumors are usually benign and can be addressed by a health care provider.

A late or missing period may even be a sign that you are entering perimenopause. This is the stage before menopause when the reproductive hormones decline, explains Joanne Armstrong, M.D., MPH, an OB-GYN, vice president, and chief medical officer of Women's Health and Genomics at CVS Health. 

“During the perimenopausal years—typically anytime after age 40—ovarian function becomes more erratic and progressively diminishes and hormone levels drop,” says Dr. VanRooyen. “The average age of menopause in the United States is 51, so there is generally a decade or more of changing hormone production as you get older, and menstrual irregularities are more common in this age range.”5

Ectopic Pregnancy

Occurring in about 1 to 2% of pregnancies, an ectopic pregnancy can also cause a negative pregnancy test result.6 With this type of pregnancy, the embryo typically implants in the fallopian tubes instead of the uterus, but it can happen elsewhere as well. “The likelihood of an ectopic pregnancy is increased by anything that causes scarring or damage to the fallopian tubes, like previous infection or surgery,” says Dr. VanRooyen. 

An ectopic pregnancy does not develop correctly and is not viable. Not only is the formation of the placenta delayed, but the production of the pregnancy hormone—human chorionic gonadotropin (hCG)—is disrupted. It also can be dangerous if it leads to a rupture of the fallopian tube.

“The ectopic initially grows like a normal pregnancy, but once it reaches a certain size, it cannot develop any further as the fallopian tube is not designed to expand like a uterus,” says Dr. VanRooyen. “This leads to increasing pain, bleeding, and frequently, if left untreated, rupture of the fallopian tube, which can be a life-threatening emergency.” 

Contact a health care provider immediately or go to the nearest emergency room if you have missed a period and also experience severe abdominal pain, fainting, dizziness, nausea, vomiting, along with sudden vaginal bleeding. These could be signs of an ectopic pregnancy. 

Medical Conditions

Various disorders, including polycystic ovary syndrome (PCOS), also can cause abnormalities in your cycle, says Dr. Armstrong. “PCOS is a hormonal disorder impacting the ovaries and causes missed periods due to lack of ovulation and higher levels of androgens.” 

Endometriosis (abnormal tissue growth outside the uterus), Von Willebrand disease (a blood clotting disorder), and endometrial cancer (cancerous cells found in the uterus lining) can all cause irregular, heavy, or missed periods as well, she points out.