Why Is My Period Late

Why Is My Period Late? (It’s Not Always Pregnancy)

It is a common scenario: you track your cycle, expect your period, and it doesn't arrive. While pregnancy is the first assumption for sexually active individuals, a delayed menstrual cycle is often the body’s response to internal or external shifts.

A "normal" cycle ranges from 21 to 35 days. A period is generally considered late if it is more than five days past your expected start date, and "missed" if you go six weeks without bleeding.

Here are the clinical reasons your cycle might be delayed, excluding pregnancy.

1. Stress and the Hypothalamus

Chronic physical or emotional stress triggers the production of cortisol. High cortisol levels can suppress the hypothalamusthe part of the brain that controls the pituitary gland. This disruption halts the production of Gonadotropin-releasing hormone (GnRH), delaying or stopping ovulation. If you don't ovulate, your period will be delayed.

2. Significant Weight Changes

• Low Body Weight: Excessive exercise or drastic calorie restriction can lead to functional hypothalamic amenorrhea. When body fat drops too low, the body shuts down reproductive functions to conserve energy.
• Overweight/Obesity: Adipose tissue (body fat) produces estrogen. Excess estrogen can interfere with the feedback loop to the brain, causing irregular periods.

3. Polycystic Ovary Syndrome (PMOS)

PMOS is a leading cause of irregular cycles. It involves an imbalance of reproductive hormones (often elevated androgens) which prevents the egg from maturing or releasing during the follicular phase. Without ovulation, the uterine lining does not shed on a predictable schedule.

4. Thyroid Dysfunction

The thyroid gland regulates the body's metabolism and interacts closely with reproductive hormones.

• Hypothyroidism (Underactive): Can cause heavier and more frequent periods, but also delayed cycles due to elevated prolactin levels.
• Hyperthyroidism (Overactive): Often leads to scanty, short, or missed periods.

5. Perimenopause

For women in their late 30s or 40s, a late period may be the onset of perimenopause. As ovarian reserve diminishes, estrogen levels fluctuate, and cycles often become longer or skip entirely before menopause is reached.

When to See a Doctor

Occasional irregularity is common. However, clinical guidelines suggest consulting a healthcare provider if:

• You miss three or more periods in a row.
• Your cycles are consistently shorter than 21 days or longer than 35 days.
• You experience severe pain or unusual discharge.

References

1. American College of Obstetricians and Gynecologists (ACOG). (2020). Amenorrhea: Absence of Periods.
2. National Institute of Child Health and Human Development (NICHD). (2017). What causes menstrual irregularities?
3. Mayo Clinic. (2023). Menstrual cycle: What's normal, what's not.
4. Klein, D. A., & Poth, M. A. (2013). Amenorrhea: An approach to diagnosis and management. American Family Physician, 87(11), 781-788.