It’s not uncommon for women to have menstrual cycles that vary in length. One month it might be 28 days — which is considered average — and the next month it could be 31 days, and the next 27. That’s normal.
Menstrual cycles are considered irregular when they fall outside the “normal” range. The Office on Women’s Health reports that an irregular menstrual cycle is one that’s shorter than 21 days or longer than 35.
When counting the days in your cycle, the first day of bleeding is day one, and the last day of the cycle is the first day of bleeding in your next cycle.
It’s possible to become pregnant when you have an irregular menstrual cycle, but you may find it difficult. If you’re unsure about the length of your cycle from month to month, it can be difficult to know when you’re ovulating.
Timing intercourse around ovulation can increase your chances for pregnancy since you’ll need to have sex during your fertile window to conceive. Your fertile window refers to a few days before ovulation and the day you ovulate.
An irregular menstrual cycle may also be a sign of irregular ovulation. You may not ovulate every month or you may ovulate at different times from month to month.
Irregular periods and ovulation
It’s possible to ovulate without later bleeding like a period. This often occurs because of previous uterine scarring or certain hormonal medications.
It’s also possible to have menstrual-like bleeding without ovulation. This generally happens when the uterine lining becomes so thick it becomes unstable and naturally sloughs off.
The uterine lining can become thick without ovulation if the hormone estrogen, which is produced prior to ovulation, continues to be secreted unopposed by the other female hormone, progesterone, which is produced after ovulation.
There are many possible causes for irregular menstruation, and many of the causes can affect ovulation or make getting pregnant more difficult. In some cases, the cause of irregular menstruation is unknown.
Some causes that may affect ovulation and your ability to carry a pregnancy include:
Polycystic ovary syndrome (PCOS)
PCOS is a condition in which the female body secretes too many androgens. Androgens are sometimes thought of as “male” sex hormones. Too many androgens can prevent mature eggs from developing and being released by the fallopian tubes.
PCOS, which affects up to 21 percent of women, is the most common cause of infertility from lack of ovulation. PCOS can be a genetic disorder, but it can also be influenced by lifestyle factors, such as being overweight and sedentary.
Perimenopause is the time in a woman’s reproductive life when estrogen and progesterone naturally decline. This causes irregular ovulation and periods before they stop altogether, signaling menopause. Typically, perimenopause lasts about four years, but some women can go through it for much longer.
The average age of the onset of perimenopause is 47, with 51 being the average age of the final menstrual period. Perimenopause ends — and menopause begins — when you haven’t had a period for 12 months.
Symptoms of perimenopause may include:
While it’s still possible to become pregnant during perimenopause, it can be more difficult because the released eggs will be older and potentially less viable. You also may not release eggs with every cycle.
Your thyroid, which is a small butterfly-shaped organ at the base of your neck, helps regulate hormones that, among other things, impact ovulation and menstruation. In one study, nearly 14 percent of adolescent girls with thyroid disorders also had irregular periods.
Other symptoms of thyroid disease, which include hyperthyroidism and hypothyroidism, can be:
altered heart and metabolic rates
Being severely over- or underweight can set off a chain reaction in your body that interrupts hormonal function. That can lead to absent or irregular ovulation, which can also lead to absent or irregular menstruation.
According to research published in BMC Women’s Health, women with a body mass index of less than 20 or greater than 25 were at least 1.1 times more likely to experience menstrual irregularities than women who had BMIs between 20 and 25.
Stress can impact a wide variety of bodily functions, including ovulation. In one study looking at medical students, those who reported higher levels of perceived stress were more likely to have menstrual irregularities compared with those who didn’t feel highly stressed.
How to get pregnant with irregular periods