Why Is My Period Late? 6 Possible Reasons (Besides the Obvious One)

Periods can be—quite literally—a pain. Still, even though many of us dread that time of the month, not getting a period when you’re expecting to can be stressful. And no, pregnancy isn’t always the culprit.

Below, six reasons—other than pregnancy—that your period might be late, according to Dr. Mary Jacobson, Chief Medical Advisor at Alpha Medical, a healthcare company formed with the goal of providing access to care for some of the country’s most common, underserved and undertreated medical needs.

Dr. Mary Jacobson is the Chief Medical Advisor at Alpha Medical. She received her medical degree from Georgetown University School of Medicine, and is an accomplished academic, board-certified obstetrician and gynecologist with extensive experience in clinical care, medical education, hospital operations and research. She completed her residency and fellowship at the Stanford University School of Medicine.

Women in perimenopause may have delayed menstrual periods due to a natural decline in ovarian function. “Perimenopause begins with the onset of menstrual irregularities which can last for up to eight years,” Dr. Jacobson tells us. “The physiologic changes of the menopausal transition are primarily due to a decline in ovarian function represented by ovarian follicles.” She explains that women are born with a finite pool of follicles during fetal life. Atresia, or the degeneration of ovarian follicles which do not ovulate during the menstrual cycle, leads to a continuous decline of ovarian follicles over a woman’s reproductive life. “The rate of decline accelerates during the years preceding menopause represented by an increasing interval between menstrual periods leading up to the last menstrual period of her life,” Dr. Jacobson notes.

Per the U.S. Department of Health & Human Services, “Polycystic ovary syndrome (PCOS) is a health problem that affects one in ten women of childbearing age. Women with PCOS have a hormonal imbalance and metabolism problems that may affect their overall health and appearance. Dr. Jacobson explains that women with PCOS often have higher levels of androgen (male hormones), which can: 

• Disrupt the menstrual cycle
• Impair ovulation
• Cause difficulty getting pregnant
• Cause male pattern hair growth or scalp hair loss
• Increase a woman’s risk of developing diabetes, high blood pressure or high cholesterol

The most common sign of PCOS, she notes, are period problems. “Irregular or infrequent menstruation is directly related to hormone imbalance,” Dr. Jacobson says. “Some women experience light periods because they are not ovulating, and some women may experience extremely heavy menstruation because the lining of the uterus continues to thicken during missed periods.” She adds that women with PCOS typically have fewer than six to eight cycles in a year. 

If you’re new to the world of having periods, it’s not unusual to have an irregular cycle for a little while. Dr. Jacobson explains, “During the first two years of menarche (the age of a woman’s first menstrual period), the positive feedback response to estrogen, which allows ovulation, can cause menstrual irregularity.” Basically, it’s totally normal if, in the year or two after getting your first period, your body doesn’t immediately fall into a regular cycle.

Just because you’ve given birth after not having a period for ten-ish months doesn’t mean your cycle will bounce right back to its pre-pregnancy schedule. “Suckling delays resumption of menstrual periods after delivery by disrupting the normal pattern of release of gonadotropin releasing hormone (GnRH) by the hypothalamus,” Dr. Jacobson says. “This leads to a disruption in the pattern of pulsatile release of luteinizing hormone (LH) from the pituitary. The inadequate pulsatile LH signal results in a reduced estradiol production by the ovarian follicles.” In laymen’s terms, breastfeeding your child can prevent your hormones from returning to their pre-baby levels, leading to an irregular cycle.

EDs are classified according to Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-V), as Anorexia Nervosa (AN), Bulimia Nervosa (BN), Binge Eating and Other Specified Feeding or Eating Disorders. Folks struggling with one or more eating disorder, Dr. Jacobson notes, sometimes have an energy deficit that results in the suppression of hypothalamic secretion of GnRH, which can lead to irregular periods or even amenorrhea, the absence of menses three months or more in a row.

Dr. Jacobson tells us that there are a few medications that suppress ovarian function, leading to menstrual irregularities. These include:

• Hormonal contraceptives, which inhibit ovulation by suppressing luteinizing hormone (LH) secretion from the pituitary and thinning the endometrium (the inner lining of the uterus that women shed as a period). 
• Gonadotropin-releasing hormone (GnRH) agonist or GnRH antagonist therapy, which can be used as part of endometriosis or breast cancer treatment in some premenopausal women.
• Aromatase inhibitors, which are also used in premenopausal women with estrogen-sensitive breast cancer and block the synthesis of estrogen from ovarian and adrenal androgens.

Dr. Jacobson tells us that according to the American College of Obstetrics and Gynecology, you should follow up with a clinician trained in women’s reproductive health if: 

• Your periods were regular each month and then they stopped being regular.
• Your period comes more often than every 21 days or less often than every 45 days.
• Your periods come more than 90 days apart, even for one cycle.
• Your period lasts more than seven days.
• You are 14 or older, have never had a period and you have an eating disorder, exercise a lot or have hirsutism (excessive body hair growth).