Irregular Periods and Trying to Conceive

The honest picture, with numbers

Irregular cycles are not a vague inconvenience. They are the most common visible sign of an ovulation problem, and ovulation problems are among the most treatable causes of difficulty conceiving. That combination — clearly signposted and often treatable — is worth knowing before you spend another year assuming nothing can be done.

The definitions first. The NHS defines periods as irregular if the gap between them is less than 21 days or more than 35 days. The FIGO classification, used internationally, puts normal cycle length for people aged 18 to 45 at 24 to 38 days, with anything under 24 days counted as frequent menstruation, anything over 38 days as infrequent, and cycles that vary by more than 7 to 9 days counted as irregular.

The reason this matters for conception is mechanical: the NHS puts it as getting pregnant can be more difficult with irregular periods because you might not release an egg regularly. Not never — irregularly. Many people with irregular cycles do ovulate, but unpredictably, and some cycles are anovulatory while others are not.

PCOS is the single largest cause, affecting 8% to 13% of women of reproductive age according to the FIGO review. But it is not the only one, and assuming PCOS without testing is a common way to end up on the wrong treatment.

What actually affects it

Where the problem sits

The FIGO system sorts ovulatory disorders by where they originate — hypothalamus, pituitary, ovary, or PCOS, which is kept as its own category because it cannot be confined to an ovarian origin. That structure is useful to you because the treatments differ completely by category. Hypothalamic problems driven by low body weight or heavy exercise are managed differently from pituitary problems driven by high prolactin, which are managed differently again from PCOS.

The causes the NHS lists

Common causes of irregular periods include puberty, the approach of menopause, pregnancy, hormonal contraception such as the progestogen-only pill, the injection and the IUS, losing or gaining a lot of weight, stress and anxiety, exercising too much, and conditions including PCOS and thyroid problems.

Two causes with specific treatments

NG257 gives clear recommendations for two categories. For hypogonadotropic hypogonadism with anovulatory infertility, it advises that increasing body weight towards a healthy weight if BMI is under 18.5, and moderating exercise levels if these are high, may improve the chance of regular ovulation, conception and an uncomplicated pregnancy — and it recommends gonadotrophins with LH activity, or gonadotrophin releasing hormone, to induce ovulation. For ovulatory disorders caused by high prolactin, it recommends cabergoline.

The PCOS gap in the current guideline

Worth knowing so you are not confused at an appointment: NG257 has removed its recommendations on ovulation induction for hypothalamic-pituitary-ovarian dysfunction, predominantly PCOS, because NICE is developing a separate PCOS guideline. In the meantime, the 2023 international evidence-based PCOS guideline — developed with ASRM, ESHRE and others — makes letrozole first-line for ovulation induction in anovulatory PCOS with no other infertility factor.

Thyroid problems

The NHS lists irregular or heavy periods among the common symptoms of an underactive thyroid. NG257 advises offering thyroid function tests only to people with symptoms of thyroid disease, so mention the symptoms rather than assuming a screening test will be done automatically.

Getting an actual answer

Home tracking is at its least useful precisely when cycles are irregular, because every method assumes a pattern. Blood tests answer the question.

• Serum progesterone, correctly timed. NICE recommends a mid-luteal progesterone test — day 21 of a 28-day cycle — to confirm ovulation even in people with regular cycles. With prolonged irregular cycles, NICE advises the test may need to be taken later, for example day 28 of a 35-day cycle, and repeated weekly until the next period starts. A single badly timed test is the most common reason people are wrongly reassured.
• Serum gonadotrophins. NICE recommends offering people with irregular cycles a blood test measuring FSH and luteinising hormone.
• Prolactin, only if indicated. NICE advises against routine prolactin testing, and recommends it only for people with an ovulatory disorder, galactorrhoea or a pituitary tumour — which, if your cycles are irregular, may well include you.
• Ovulation kits are the weakest option here. Persistently raised LH in PCOS produces false positives, and with a long cycle you may not know which week to test.
• Basal body temperature. NICE advises against using BBT charts to confirm ovulation. Across several anovulatory cycles you may see no rise at all — which is itself information worth bringing to an appointment.

What to do next

1. Record six months of dates — first day of each period, and the length of each gap. This one page changes what a clinician can do at a first appointment.
2. Ask for progesterone testing timed to your actual cycle length, repeated weekly if your cycles are long, rather than an automatic day-21 test.
3. Ask for FSH and LH, which NICE recommends specifically for irregular cycles.
4. List any symptoms of thyroid disease — tiredness, feeling cold, weight change, dry skin, low mood — because that is what triggers thyroid testing under NG257.
5. Have a semen analysis done at the same time. Ovulation treatment recommendations generally assume no other infertility factor, and that assumption needs testing.
6. Have intercourse every 2 to 3 days across the cycle. NICE recommends this generally, and it is particularly suited to irregular cycles because it removes the need to predict a day you cannot predict.

When to seek help

Do not wait a year. NG257 recommends referral at first presentation if either partner has a suspected or known clinical cause of infertility or a history of predisposing factors. Irregular or absent periods in someone trying to conceive is exactly that. The NHS also advises seeing a GP if your periods are irregular and you are struggling to get pregnant.

Go sooner still if your periods have stopped altogether, if the gaps are longer than three months, if you have symptoms such as excess hair growth, galactorrhoea or severe pelvic pain, or if you have had cancer treatment or pelvic surgery. Irregular cycles are a reason to be investigated earlier than the standard timetable, not a reason to be told to keep waiting.