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What causes irregular periods?

11 January 2021

It is well known that regular menstrual cycles are between 21 to 35 days, with an average length of 28 days, however, this only actually works for 12% of women. Everything else, periods before 21 days or after 35 days, is considered irregular. Sometimes, having irregular periods makes us anxious as we do not understand why this happens. It is also difficult to predict our ovulation, especially when we are trying to conceive. The aim of this article is to find out what could cause irregular bleeding. Some causes can be physiological, others can be treated or managed. Let's discover them here!

Most common causes of irregular periods…

  1. Puberty: After the first menstrual period in adolescence (called menarche), cycles can be irregular for the first year or two – this is considered normal and physiological. If periods are irregular 2 years after menarche, other causes might have to be ruled out.
  1. Peri-Menopause: This is the time before you enter Menopause, which is on average, around 51 years old in the UK. Sometime before this normal stage, periods tend to get irregular, sometimes longer, and sometimes shorter. This is due to the fluctuation in Oestrogen levels. These irregular periods are often accompanied by hot flushes, night sweats, mood changes or vaginal dryness. If you are younger than 40 and have these symptoms, see your doctor to rule out premature ovarian insufficiency, popularly known as, early menopause.
  1. Change in your weight (eating disorders): Obesity and rapid weight gain can cause menstrual irregularities. Both affect hormone and insulin levels and are common signs of PCOS. Conversely, extreme weight loss and eating disorders can also trigger irregular periods or frankly amenorrhea (no periods at all). If you have any eating disorder, or you are underweight (BMI less than 18.5) or you are losing weight without even trying, you should see your doctor.
  1. Excessive exercise: Vigorous exercise interferes with the hormones responsible for the menstrual cycle and can be the cause of why you are missing periods. Female athletes or marathon runners who train very frequently can present irregular periods or a lack of periods. The reason is the interruption of the hypothalamic-pituitary-ovarian axis where the hormonal message sent from the brain does not reach the ovaries, and therefore ovulation does not occur. If you reckon you are doing too much physical activity, try cutting it down and see what happens. If your period still does not recover, see your doctor.
  1. Stress: Similar to exercise, stress and anxiety might affect the hormones at the brain level, causing irregularity in your menstrual cycle or amenorrhea. Stress relief techniques might help both, improving quality of life and the recovery of periods. 
  1. Early pregnancy: Sometimes, the first sign of pregnancy is abnormal bleeding, if you see bleeding (also spotting) which is not normal for you, take a pregnancy test.
  1. Breastfeeding – high prolactin levels: A breastfeeding woman has high levels of prolactin, a hormone which is responsible for breast milk production. Prolactin interferes with reproductive hormones and affects menstrual cycles. Suppose you are not breastfeeding but can see milk discharge from your breast, or have irregular or no cycles at all, or have abnormal hair growth. In these cases, you might have a high level of prolactin, also called hyperprolactinemia and you should see your doctor to find out more and manage it.
  1. Contraception: It is expected to see some abnormal bleeding or spotting when we start contraception, pills or coils. This usually settles after 6 months.
  1. PCOS: Irregular periods are a common sign of PCOS, but as you can see, not all irregular periods are PCOS. This syndrome can also include excess facial and body hair, weight gain, obesity, and acne. See our articles about PCOS on the blog for more information.
  1. Thyroid dysfunction: Hypothyroidism (underactive thyroid) or Hyperthyroidism (overactive thyroid) can cause irregular periods or amenorrhea. In hypothyroidism, you can also feel tired, cold, and experience weight gain. In hyperthyroidism, you can see shorter or lighter periods, plus you may experience weight loss, palpitations and anxiety.
  1. Uterine pathology: Fibroids or polyps are common pathologies in the womb. Fibroids are benign muscular tumours in the womb’s wall, and almost 70% of women have them. They can present with heavy periods, even with secondary anaemia, pelvic or back pain or pain during sex. Polyps, on the other side, are a benign overgrowth of the lining of the womb, which can cause irregular periods, bleeding between periods or during sexual intercourse. Any pathology in the womb can be assessed by pelvic ultrasound.
  1. Endometriosis: This disease affects 10% of women of reproductive age. It is characterised by the presence of endometrial tissue (lining of the womb) outside the uterus. Typically, it causes very painful period pain, but it can also present with heavy bleeding or irregular bleeding between periods. Endometriosis is also an important cause of infertility. 
  1. Cervical or Endometrial cancer: One of the first signs of gynaecological cancer is abnormal bleeding between periods or after sex. If you are concerned, speak to your doctor and make sure your smear test is updated.

When should I see my GP or fertility doctor?

If you are concerned you might have one of the causes above, seek professional advice to rule it out. If you are breastfeeding or in the middle of the puberty or if you started a new form of contraception within the last 6 months, these irregular periods might be normal. If you think it could be something else, you should speak to your GP or fertility doctor.

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