Causes of infertility

To achieve a natural pregnancy the following are needed:

  1. The release of an egg
  2. Good quality sperm
  3. Healthy Fallopian Tubes
  4. Regular sexual intercourse

It sounds relatively simple but many synchronised events must take place and there are several steps where things may go wrong.

Infertility is defined as the failure to conceive after one year of having regular, unprotected intercourse.

Around 1 in 6 couples in Northern Ireland have difficulty in conceiving. This proportion is increasing, largely because people are starting their families later in life and sperm counts are falling. However, with the appropriate help, the many couples will achieve a pregnancy.

There are many reasons why there may be difficulty conceiving but broadly these can be attributed to problems of ovulation, egg quality, sperm quality, damaged Fallopian tubes or a combination of these factors.

Common egg problems:

  • Polycystic ovary syndrome (PCOS) (for further information please click here).
  • Being over- or underweight
  • Medications that affect ovulation
  • As a woman gets older, the quality of her eggs decreases.

Common sperm problems:

  • Too few or no sperm
  • Not enough motile (active) sperm
  • Minor genetic problems that affect sperm counts and quality

Common Fallopian tube problems:

  • Past pelvic infection
  • Pelvic surgery


Endometriosis is a common condition where the cells that line the womb (and bleed each month with a menstrual period) occur outside the womb. Even mild endometriosis can have a negative effect on a couple’s fertility.

Unexplained infertility

In a proportion of couples, an obvious cause cannot be found, this is termed "unexplained infertility". It doesn’t mean that there is nothing wrong, it just reflects our current state of knowledge and may be due to a subtle problem that is not yet detectable.