Causes of Infertility: The Main Reasons Couples Struggle to Conceive

Infertility usually has an identifiable cause, and that cause can lie with either partner or with both: the main groups are ovulation disorders, damaged fallopian tubes, conditions of the womb such as endometriosis, a problem with sperm, the effect of age, and cases where no clear reason is found. Often more than one factor is present at once, which is why both partners are investigated together. When my own results came back, the hardest part was not the diagnosis; it was realising how many separate things have to go right. This guide walks through each main cause and roughly how common it is.

Ovulation disorders

Problems with releasing an egg are one of the leading causes of infertility in women. If ovulation is irregular or absent, there is no egg to fertilise in a given month. The most common underlying reason is polycystic ovary syndrome (PCOS), which the NHS estimates affects around 1 in 10 women of reproductive age. Thyroid problems, very high or low body weight, and a hormone called prolactin can also disrupt the cycle. The usual clue is irregular, infrequent, or absent periods, so tracking your cycle is genuinely useful information to bring to an appointment. We cover this further in PCOS and fertility and in how to get pregnant when trying to conceive.

Tubal and pelvic factors

Damaged or blocked fallopian tubes stop the egg and sperm from meeting. The tubes can be scarred by previous pelvic infection (often from chlamydia), by past surgery, or by an ectopic pregnancy. Tubal factors are thought to account for roughly 1 in 5 cases of female infertility, and they are one reason untreated sexually transmitted infections matter so much. Because the tubes cannot easily be felt or seen on a standard scan, they are checked with a specific test that looks at whether they are open; you can read what that involves in fertility tests and investigations.

Uterine factors and endometriosis

Conditions affecting the womb and surrounding tissue can make it harder to conceive or to carry a pregnancy. Endometriosis, where tissue similar to the womb lining grows elsewhere in the pelvis, affects roughly 1 in 10 women of reproductive age according to the NHS, and it is associated with reduced fertility. Fibroids, polyps, and scarring inside the womb can also play a part, depending on their size and position. Endometriosis often comes with painful or heavy periods, though not always, and the link between it and fertility is covered in endometriosis and fertility.

Male factor infertility

A problem with sperm is involved in about a third of couples who struggle to conceive, on its own or alongside a female factor. The issue may be a low sperm count, poor movement (motility), abnormal shape, or, less often, no sperm in the ejaculate at all. Causes range from previous infection or injury to genetic factors, certain medications, and lifestyle factors. A semen analysis is one of the simplest and most important early tests, which is why both partners should be assessed from the start. There is much more detail in male factor infertility.

Age

Age is one of the strongest single factors in fertility, particularly for women. The number and quality of eggs fall over time, so fertility declines steadily through the 30s and more sharply from the late 30s; this also raises the chance of miscarriage. Male fertility declines too, but more gradually. Because the effect of age compounds over time, it is one of the main reasons clinicians advise against delaying. We go deeper in age and fertility.

Unexplained infertility

Sometimes every standard test comes back normal and no cause is found. This is called unexplained infertility, and it accounts for around 1 in 4 couples investigated for fertility problems. It can be one of the most frustrating outcomes to hear, because there is nothing concrete to point at or fix. It does not mean nothing can be done: treatments such as IUI or IVF are often still effective. You can read more in unexplained infertility.

When to seek help

Because some causes are time-sensitive, it is better to be assessed early than to wait. NICE advises seeing a GP after a year of trying without success, or after about six months if the woman is over 36, or sooner if there is a known reason for concern such as absent periods or a previous pelvic infection. Getting checked does not commit you to treatment; it simply tells you what, if anything, is going on. See when to see a doctor about fertility for the full picture.

This guide is general information and support, not a diagnosis or individual medical advice. If you are concerned about your fertility, please see your GP or a fertility specialist, who can assess you and your partner together.