Causes of infertility

If you've had regular, unprotected sex for a year without falling pregnant, then you may have a fertility issue.

Try not to worry though. Problems with conceiving are much more common than you may realise. Around one in six couples experience some difficulty in achieving a pregnancy, but the good news is that we can help almost 90% of them to achieve their dream of starting a family.


What is Infertility?

Infertility can be defined as the inability to conceive despite having regular unprotected sex for a year or more. For some, getting pregnant can take some time, but we recommend seeking help if you have been trying for over a year.

What are the causes of infertility?

There are many reasons for infertility, and it can affect both men and women. Conception occurs when the female partner produces an egg from one of her ovaries and the male partner has a high number of good quality sperm to fertilise the egg. After fertilisation has occurred, the embryo then implants in the womb where it develops. If any of these processes are compromised at any stage, the chances of conception are reduced. 

Infertility - Did you know?

Around 30% of infertility is caused by female factors, around 30% to male, 20% combined male and female and 20% is unexplained.

Find out more in our Fertility Facts blog

Answering your top infertility FAQs

Charles Kingsland and Alison Campbell host a Facebook Live event at CARE Fertility Manchester.

Causes of Female Infertility


Fertility and Age

The most common reason for female infertility is age. Studies have shown that fertility begins to decrease after the age of 35, and by the age of 40 is in significant decline.

The main explanation for age-related infertility is simply the approaching end of a woman’s reproductive life. Women are born with their lifetime supply of eggs, which sit in the ovaries at different stages of development and diminish in quantity and quality with age. Ovarian reserve is a measure of female fertility during the reproductive years and can be tested by hormone levels and ultrasound through our female IVF diagnostic tests.



Problems with ovulation are one of the most common causes of infertility for women. Poor egg quality, failure to ovulate through hormonal deficiency or imbalance, irregular ovulation and Polycystic Ovary Syndrome (PCOS) are commonly encountered problems.

After a full fertility assessment, treatment can include IVF, ovulation induction or IVF with donor eggs.


Womb and Fallopian tubes

Your Fallopian tubes carry eggs from your ovaries to the womb and can be blocked or damaged, reducing the chances of eggs meeting sperm. Possible reasons include:

• scar tissue
• endometriosis
• pelvic inflammatory disease
• adhesions from an operation
• damaged tube ends
• pelvic or cervical surgery
• submucosal fibroids

If you've previously been sterilised and had the procedure reversed, remember that it will not necessarily mean that you will become fertile again.

Treatment is usually by IVF, however sometimes if the problem is a blockage, and it is very localised, then it can be possible to clear it by keyhole surgery.


Endometriosis is a condition where tissue that normally grows in the uterus implants and grows in other places in your body and can cause scarring, which may block your fallopian tubes. Mild cases of Endometriosis can be treated with a procedure known as a laparoscopy. More severe cases however can cause more serious fertility issues.


Too many people experience the heartbreak of miscarriage. It isn’t really possible to know exactly how many miscarriages occur because sometimes a miscarriage can happen before pregnancy is confirmed. Studies indicate that miscarriage occurs in around 1 in 4 recognised pregnancies, with 85% of those happening in the first trimester (weeks 1 to 12).

In the first 12 weeks, the most common cause of  miscarriage is an issue with development of the embryo.

However, physical complications or health issues including shape of the uterus, diabetes, thyroid disease, hormonal problems, or immune conditions can also cause miscarriage.

 Our recurrent miscarriage tests are designed to investigate the underlying cause of miscarriage and help us identify appropriate treatment options. We may recommend PGT-A (Preimplantation Genetic Testing). This test gives us information about the genetic health of embryos to help us identify embryos which have the correct number of chromosomes (chromosomes are very important for healthy growth and development).

CAREunity is a test which  looks at a genetic  "variation" in a specific gene (Annexin A5) which is partly responsible for normal clotting in our body. The presence of the variant gene can be associated with blood clotting disorders (sticky blood). Increased clotting in the placenta can lead to miscarriage or implantation failure by reducing the blood flow to the embryo at a very early stage of its implantation in the womb.

When you have been through miscarriage, having lots of support is really important. Talk to your family and friends family about how you are feeling, or you might want to reach out to a support organisation.

You can read one of our patient stories here.

You may also want to consider having a consultation with one of our specialists.


Professor Charles Kingsland discusses miscarriage


The drugs involved with chemotherapy can sometimes cause ovarian failure which, sadly, can be permanent. Advances in egg freezing of course now mean that if you have to undertake a course of chemotherapy you can take the precaution of freezing eggs in advance of your treatment.


Overall health

Being overweight, being seriously underweight, smoking, and drinking too much alcohol can all have a negative impact on your fertility. Read more about our top tips for improving fertility.

Causes of Male Infertility

Sperm Quality & Quantity

The most common cause of infertility in men involves abnormal or insufficient sperm. Problems can arise when either not enough sperm is being produced, or the sperm is of poor quality. The motility can be low, which affects the sperm's ability to ‘swim’ as vigorously as it needs to, or the sperm can be abnormally shaped. A normal sample will show ~20 million sperm per millilitre, at least half of which will be active.

Intra-Cytoplasmic Sperm Injection (ICSI) can help to overcome certain male fertility problems caused by low sperm count or poor sperm qualityThere are also a range of male diagnostic tests we can perform to identify if there are any issues with the sperm.


Blocked tubes

Either the tubes which store and carry your sperm from your testicles, or the vas deferens which lead from them and carry sperm immediately prior to ejaculation can be blocked. If everything else is healthy then a simple procedure to retrieve sperm may be the recommended way forward.


The testicles produce and store your sperm. If they are damaged it will affect the quality and quantity of the sperm you produce. The damage could be caused by a wide number of events such as an infection or a testicular operation. If this is the case, it may still be possible to retrieve sperm surgically.


Sulfasalazine used to treat rheumatoid arthritis and Crohn's disease can decrease your sperm count, however the effects are only temporary and you should return to normal after your course of treatment. Long term use and abuse of anabolic steroids will reduce the number of sperm you produce and affect their motility.

The drugs involved with chemotherapy can severely reduce your production of sperm, however advances in sperm freezing now mean that if you have to undertake a course of chemotherapy you can take the precaution of freezing sperm in advance of your treatment.

Next steps

When you’re ready, talk to us. We will give you the information and support you need together with clear guidance on what we need to do together to achieve the best chance of success for you.

It's simple to get started with CARE:

Book a consultation


Or contact our new patient enquiry team on 0800 654 2270

Treatment criteria 

Whilst we aim to help everyone, there are some situations where we are unable to treat certain patients. These criteria are outlined below:

  • Anyone who has a serious, pre-existing medical condition that would make it unsafe for them to become pregnant. If you think that this may apply to you then the first step might be to seek advice from your GP or an obstetrician.
  • Anyone who has a serious, pre-existing medical condition or a serious allergy which would make it unsafe for them to undergo a procedure under conscious sedation in one of our CARE clinics. Not all of our treatment options will need you to have a procedure (if you have an ovulation induction, treatment with donor eggs or surrogacy for example) but if you think that this may apply to you then let our appointments team know and they can seek some advice before making your appointment.
  • Anyone with a BMI over 30 is encouraged to lose weight before treatment as success rates are better and pregnancy is safer. We do not offer treatment to  enable a woman to become pregnant or involving a procedure under conscious sedation with a BMI above 35 because of the increased risks of treatment and pregnancy.
  • We ask all women aged more than 50 years who are seeking treatment to carry a child to see an obstetrician to get advice on the advisability and safety of a pregnancy in their individual circumstances
  • We can only provide treatment where a child born as a result of that treatment will have one legal parent who is aged 55 years or under.  This is because we want to make sure that children born as a result of the treatment we provide have a good chance of having a living parent up to the age of adulthood.
  • We can’t treat anyone aged less than 18 years old. This is because our registration with the Care Quality Commission only permits us to treat people aged 18 years or over.