Pregnancy is one cause of a late period, but there can be many other factors to consider.
The average menstrual cycle lasts about 28 days, but it can vary from person to person.
Keeping track of periods can help a person determine the length of their cycle and recognize any irregularities.
Keep reading to learn more about the causes of late periods and when to seek medical attention.
When someone starts getting their period for the first time, it can take a few months or years before their cycle becomes regular.
According to The American College of Obstetricians and Gynecologists, a typical menstrual cycle lasts 28 days. However, depending on the person, a healthy cycle may last 21–45 days.
Many people track their periods to check for any changes in their cycle. Some smartphone apps make tracking easier.
Anyone who notices changes in their cycle should consult a doctor.
Amenorrhea is the medical name for an absence of periods. If a female does not start menstruating by 16 years of age, a doctor may diagnose “primary” amenorrhea.
If a person who was having periods suddenly stops menstruating, the doctor may refer to this as “secondary” amenorrhea.
It is important for a person to see a doctor if they have missed more than three periods in a row.
A variety of factors can disrupt a person’s menstrual cycle. Periods may come back on their own, but if delays are persistent, a doctor — such as a gynecologist — should explore the possible causes.
A late period can indicate pregnancy. However, other circumstances and medical conditions can also lead to late or missed periods. The following can have this effect:
Birth control medications
These medications prevent pregnancy by stopping ovulation, and they can also disrupt the menstrual cycle.
For example, regular bleeding is a common side effect of some hormone-based types of birth control, such as the progesterone-only injection.
Also, stopping and starting birth control medication can cause irregularities in the menstrual cycle.
However, once a person starts taking the medication regularly, their periods may regulate as well. If periods continue to be irregular, speak with a doctor.
People approaching menopause may notice delays in their periods.
Early in the transition toward menopause, the cycle length can differ by 7 or more days each time. As the transition progresses, the time between periods increases.
Eventually, menstruation stops. Menopause begins when an individual has not had a period for 12 months in a row.
Obesity and anorexia
Research indicates that people with obesity tend to experience more menstrual irregularities than people with moderate weight.
When relevant, doctors often recommend working toward a healthy weight to people who have irregular cycles. However, if a person has obesity, losing weight may not always reverse the irregularity.
Anorexia is an eating disorder that causes weight loss or, in children, a lack of weight gain. Anorexia often develops in adolescence, but it can occur at any age.
A person with anorexia may have imbalances of two essential hormones that support the menstrual cycle and fertility: follicle stimulating hormone (FSH) and luteinizing hormone (LH).
According to the National Eating Disorders Association, one sign of anorexia is a loss of periods after puberty.
Functional hypothalamic amenorrhea
Functional hypothalamic amenorrhea is one of the most common causes of secondary amenorrhea — periods that stop.
In people with this condition, weight loss, stress, and high levels of exercise contribute to amenorrhea. These factors cause irregularities in the release of a specific hormone that causes impairment of FSH and LH.
People with functional hypothalamic amenorrhea may also have low levels of estrogen in their blood.
Doctors may also find that these people have:
- mildly high cortisol levels
- low insulin levels
- low insulin-like growth factor-1 levels
- low triiodothyronine levels
These imbalances can cause:
- menstrual irregularities
- decreased bone mass
- cardiovascular complications
- glucose metabolism irregularities
Other hormonal imbalances
Sex hormones help regulate periods, but other hormones can also affect menstrual cycles. For example, imbalances in levels of thyroid hormone or prolactin can alter the length of a cycle.
According to an older study, more than half of females with high levels of thyroid hormone — a condition called hyperthyroidism — may experience disrupted menstrual cycles, including amenorrhea.
Others with low levels of thyroid hormone — or hypothyroidism — tend to experience more frequent bleeding.
A person may have high levels of the hormone prolactin in their blood — a condition called hyperprolactinemia.
Levels of this hormone tend to rise during pregnancy and breastfeeding, but they can also spike in people who take certain medications or who have diseases of the pituitary gland or hypothalamus.
People with hyperprolactinemia may experience amenorrhea, discharge from the nipples, and low bone mass.
Polycystic ovary syndrome
- menstrual irregularities
- high insulin levels
Doctors may recommend lifestyle modifications, hormonal treatments, and the drug metformin to help regulate the menstrual cycle.
Some people with PCOS also experience infertility.
People take Plan B to prevent pregnancy following sex without contraception.
A person should take the medication within 72 hours of sex, as the efficacy of the drug decreases over time. It contains only levonorgestrel, a synthetic version of the hormone progestin.
After taking Plan B, a person can expect to get their period at the usual time, but there may be a delay of up to 1 week.
Also, some people experience spotting or bleeding between taking Plan B and getting their period.
It is important to note that Plan B is not 100% effective. If a person does not get their period within a week of taking the drug, it is probably a good idea to take a pregnancy test.
Missing a period does not always indicate pregnancy or a health issue.
Speak with a doctor if periods do not arrive by age 16 or if they stop for more than 3 months in a row.
Tracking periods can help a person recognize any irregularity. Anyone who notices a change in the length of time between periods should speak with a doctor.
Also, it is a good idea to consult a doctor if periods come more often than every 21 days or less often than every 45 days.
Amenorrhea is not life-threatening. However, the hormonal imbalances that can cause it can also lead to harmful complications, such as hip and wrist fractures.
A doctor can help identify the cause of menstrual irregularity and recommend an effective treatment or management plan.
Also, anyone who suspects that they are pregnant, even after taking Plan B, should speak with a doctor.
Menstrual irregularities are common.
Some people worry that they are pregnant or have a medical condition if they miss their period, but many other factors can contribute to a delay. Hormonal imbalances, stress, and weight loss, for example, can all play a role.
Anyone who believes that they may be pregnant or who misses more than three consecutive periods should speak with a doctor.
Tracking periods helps a person detect any changes.
A doctor can identify the cause of missed periods and recommend an appropriate course of action, if any is necessary.