Why Do Periods Get Delayed? When Should You Be Concerned?

What Is the Menstrual Cycle and How Does It Work?

Hello, I'm Dr. Emre Gecer. To understand the causes of a delayed period, you first need to know how a normal menstrual cycle works. The menstrual cycle is a complex hormonal process regulated by the hypothalamic–pituitary–ovarian (HPO) axis.

A normal menstrual cycle lasts on average 28 days (21–35 days is considered normal) and consists of four main phases:

1. Menstrual Phase (Days 1–5)

If pregnancy did not occur in the previous cycle, progesterone levels fall and the endometrium (the lining of the uterus) is shed — this is menstrual bleeding. Normal bleeding lasts 3–7 days.

2. Follicular Phase (Days 1–13)

Follicle-stimulating hormone (FSH) released by the pituitary gland stimulates the growth of several follicles in the ovaries. One of these becomes the dominant follicle and secretes increasing amounts of oestrogen, which thickens the endometrium again.

3. Ovulation (around day 14)

The peak in oestrogen levels triggers a sudden surge of luteinising hormone (LH) from the pituitary gland. About 24–36 hours after this LH surge, the dominant follicle ruptures and releases a mature egg (oocyte) into the fallopian tube — this is ovulation.

4. Luteal Phase (Days 15–28)

The ruptured follicle becomes the corpus luteum, which secretes large amounts of progesterone (and some oestrogen). Progesterone prepares the endometrium for possible implantation and slightly raises body temperature. If pregnancy does not occur, the corpus luteum regresses after 10–14 days, progesterone falls and a new menstrual cycle begins.

Important note: A disorder at any level of the HPO axis — hypothalamus, pituitary or ovary — can disrupt the menstrual cycle and cause a delayed period or amenorrhea (absence of menstruation).

The Most Common Causes of a Late Period

1. Pregnancy

In a sexually active woman of reproductive age, pregnancy is the first cause to rule out for a late period. A home pregnancy test taken from the first day of the missed period usually gives a reliable result. If it is negative and the period still does not come, it can be repeated a week later or a blood beta-hCG test can be ordered.

2. Stress

Psychological stress is one of the most common and most easily overlooked causes of a late period. Chronic stress suppresses the pulsatile release of gonadotropin-releasing hormone (GnRH) in the hypothalamus and so lowers FSH and LH levels. The condition is called "functional hypothalamic amenorrhea". Life events such as exam periods, work pressure, relationship problems, bereavement and moving house can affect the cycle. Stress management and psychological support can be effective in restoring normal cycles.

3. Polycystic Ovary Syndrome (PCOS)

PCOS is the most common endocrine disorder of reproductive-age women, affecting 6–12% of them, and the commonest hormonal cause of menstrual irregularity. Under the Rotterdam criteria, the diagnosis is made when at least two of the following three criteria are present:

• Oligo-ovulation or anovulation: irregular or infrequent menstrual cycles.
• Clinical or biochemical hyperandrogenism: acne, hirsutism (excessive hair growth), elevated androgens (testosterone, DHEA-S).
• Polycystic appearance of the ovaries on ultrasound: more than 12 small follicles in each ovary, or an ovarian volume > 10 mL.

PCOS is not just a gynaecological disease; it is a systemic condition that also increases the risk of insulin resistance, metabolic syndrome, type 2 diabetes and cardiovascular disease. Treatment includes lifestyle changes (weight control, exercise), metformin, oral contraceptives, and — if pregnancy is desired — ovulation induction.

4. Thyroid Disorders

Thyroid hormones play a critical role in the regular running of the menstrual cycle.

• Hypothyroidism (low thyroid): TSH rises, thyroid hormones (T3, T4) fall. Heavy menstrual bleeding (menorrhagia), menstrual irregularity or amenorrhea may occur. It can also raise prolactin levels and so suppress ovulation.
• Hyperthyroidism (high thyroid): TSH falls, T3/T4 rise. Infrequent periods (oligomenorrhea), light bleeding or amenorrhea may occur.

Thyroid function tests (TSH, free T4) should be ordered in every woman with menstrual irregularity. With treatment of the thyroid disease, menstrual order usually returns to normal.

5. Excessive Exercise and Low Body Weight

Intense physical activity and a low body-fat percentage can lead to hypothalamic amenorrhea. Marathon runners, ballerinas, gymnasts and professional athletes are particularly at risk. When the body-fat percentage falls below 17–22%, oestrogen production falls and ovulation may stop. This condition is also known as the "female athlete triad" (amenorrhea + eating disorder + osteoporosis) and creates serious risks for bone health.

6. Eating Disorders

Anorexia nervosa and bulimia nervosa, as serious eating disorders, suppress the HPO axis. Amenorrhea is very common in anorexia nervosa and is accepted as one of the diagnostic criteria. Inadequate calorie intake puts the body into "survival mode" and reproductive functions are shut down. Treatment requires nutritional rehabilitation and psychiatric support.

7. Premature Ovarian Insufficiency (POI)

POI is defined as a decline in ovarian function or the cessation of ovarian function before the age of 40. It affects 1% of women. The symptoms are similar to menopause: amenorrhea, hot flushes, night sweats, vaginal dryness and mood changes. Diagnosis requires an FSH level > 25 mIU/mL (typically > 40) on two separate measurements together with oligomenorrhea or amenorrhea lasting more than 4 months. Causes include autoimmune disease, genetic factors (Turner syndrome, Fragile X premutation), chemotherapy/radiotherapy and surgery.

8. Hyperprolactinaemia

Excessive secretion of prolactin from the pituitary gland disrupts GnRH pulsatility and causes oligomenorrhea or amenorrhea. The most common causes are prolactinoma (a pituitary microadenoma), hypothyroidism and medications (antipsychotics, metoclopramide, some antidepressants). Galactorrhea (milky discharge from the nipple) may accompany it. Treatment is directed at the cause; in prolactinoma, dopamine agonists (cabergoline, bromocriptine) are first-line.

9. Medications

Some medications can affect the menstrual cycle:

• Hormonal contraceptives: after stopping the birth-control pill, it may take several months for the cycle to return to normal (post-pill amenorrhea).
• Depo-Provera (medroxyprogesterone acetate) injection: can cause amenorrhea both during use and for months after stopping.
• Antipsychotics: because of their prolactin-raising effects.
• Chemotherapeutic agents: ovarian toxicity.
• GnRH analogues: used in the treatment of endometriosis, cause temporary amenorrhea.

10. Other Causes

• Asherman syndrome: intrauterine adhesions (synechiae) — usually develop after dilation and curettage and mechanically prevent shedding of the endometrium.
• Cushing's syndrome: excess cortisol production suppresses the HPO axis.
• Pituitary insufficiency (Sheehan syndrome): pituitary necrosis after excessive bleeding during childbirth.
• Chronic diseases: uncontrolled diabetes, coeliac disease, liver disease, kidney failure.
• Rapid weight changes: both weight gain and weight loss can disrupt the cycle.

Types of Amenorrhea

Primary Amenorrhea

Primary amenorrhea is defined as the failure of menstruation to begin by age 15 (if secondary sexual characteristics are present), or the failure of secondary sexual characteristics (breast development, pubic hair) to develop by age 13. Its causes include:

• Chromosomal anomalies: Turner syndrome (45,X) — the most common genetic cause.
• Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome): congenital absence of the uterus and vagina, with normal ovarian function and external genitalia.
• Imperforate hymen: absence of the hymenal opening — causing cyclic pelvic pain and haematocolpos.
• Androgen insensitivity syndrome: 46,XY karyotype with female phenotype.
• Congenital adrenal hyperplasia.
• Hypothalamic or pituitary causes.

Secondary Amenorrhea

Secondary amenorrhea is defined as the absence of menstruation for three months (in women with regular cycles) or six months (in women with irregular cycles), in a woman who previously had regular periods. Most of the causes listed above lead to secondary amenorrhea. The most common are pregnancy, PCOS, functional hypothalamic amenorrhea, hyperprolactinaemia and thyroid disorders.

Diagnostic Evaluation: What the Doctor Does

A systematic evaluation is carried out in a patient who presents with a delayed period:

• Pregnancy test: always the first step — serum beta-hCG.
• Hormonal tests: FSH, LH, oestradiol, prolactin, TSH, free T4, total testosterone, DHEA-S.
• Progesterone withdrawal test: after 10 days of oral medroxyprogesterone, the patient is assessed for bleeding. If bleeding occurs, oestrogen levels are adequate (anovulation); if no bleeding occurs, oestrogen deficiency or an outflow-tract problem (endometrium/uterus) is considered.
• Pelvic ultrasound: ovarian morphology (PCOS?), uterine structure, endometrial thickness.
• MRI: sellar MR imaging when a pituitary adenoma is suspected.
• Karyotype analysis: screening for chromosomal anomalies in primary amenorrhea or POI.

When Should You See a Doctor?

You are advised to see a gynaecologist in any of the following situations:

• If you have a regular cycle and have not had a period for 3 months in a row.
• If you have an irregular cycle and have not had a period for 6 months.
• If you have never had a period even though you are over 15 years old.
• If menstrual irregularity is accompanied by excessive hair growth, acne or weight gain (suggestive of PCOS).
• If menopausal symptoms such as hot flushes, night sweats and vaginal dryness begin before age 40.
• If you notice milky discharge from the nipple (galactorrhea).
• If menstrual irregularity is associated with visual disturbance or severe headaches (suggestive of a pituitary adenoma).
• If you are planning a pregnancy and are not sure whether you are ovulating regularly.

Lifestyle Recommendations

• Stress management: meditation, yoga, breathing exercises, regular sleep.
• Balanced nutrition: adequate calorie and nutrient intake; avoid overly restrictive diets.
• Moderate exercise: 150 minutes a week of moderate-intensity activity is enough; avoid extreme-intensity training.
• Healthy weight: both obesity and being severely underweight cause menstrual irregularity; the ideal BMI range is 18.5–24.9.
• Keep a period diary: tracking your cycle regularly helps you notice irregularities early.
• Smoking and excessive alcohol: they affect ovarian function adversely and can cause cycle irregularities.

Conclusion

A delayed period is usually a temporary and harmless event — stress, lifestyle changes and hormonal fluctuations are among the most common causes. Persistent menstrual irregularity, however, can be a sign of an underlying serious hormonal or structural problem. Pregnancy is the first thing to rule out. Conditions such as PCOS, thyroid disorders and hyperprolactinaemia are treatable, and early diagnosis can prevent complications. If your menstrual irregularity lasts more than 3 months or is accompanied by other symptoms, do not hesitate to see a gynaecologist.

Wishing you good health.
Dr. Emre Gecer

References

• Williams Obstetrics, 26th Edition — Chapter: Amenorrhea.
• Williams Textbook of Endocrinology, 14th Edition — Chapters: Female Reproductive Endocrinology; Polycystic Ovary Syndrome.
• Harrison's Principles of Internal Medicine, 22nd Edition — Chapters: Disorders of the Ovary and Female Reproductive Tract; Menstrual Disorders.
• ACOG Practice Bulletin: Evaluation and Management of Amenorrhea (2023).