Definition: when a couple who are having regular unprotected sex are unable to conceive.
The time it takes to conceive can be extremely variable throughout couples, ranging from weeks to years. Infertility can be caused by so many factors, and can wide ranging effects on couples, physiologically as well as a psychological effect.
A range of factors can affect fertility in women, ranging from acquired to genetic. Factors such as age (fertility starts to decrease after the age of 35), smoking (chemicals prevent correct oestrogen production) and sexually transmitted diseases, as well as eating disorders that increase/decrease body weight (affecting correct oestrogen production) can all affect fertility, as well as some medical treatments including chemotherapy, as well as deliberate contraceptive methods.
Genetic factors can also lead to mutations in genes involved with fertility, such as the FSHB gene , encoding the beta subunit of the Follicle Stimulating Hormone (FSH). Incorrect gene product can lead to amenorrhea, the lack of a menstrual period, and so unable to conceive due to lack of ovulation.
Conditions within the female reproductive system can affect fertility, and these can be caused by genetic or acquired factors. Physiological problems such as polycystic ovary syndrome, blocked fallopian tubes and endometriosis are to name a few, as well unknown causes. Drugs or surgery can be used to solve some of these problems and regain fertility, but in others IVF can be carried out to become pregnant.
Polycystic ovary syndrome (PCOS)
PCOS is a frequent, possibly genetic problem in women, leading to menstrual disorders and infertility, due to lack of ovulation. Those that suffer from PCOS have follicles develop within their ovaries, altering the very fine hormonal balance and often preventing ovulation. The causes of PCOS are not totally clear, with several factors thought to play a role in the cause. It is found that suffers are insulin resistant, leading to increased levels of insulin within the body, causing the ovaries to produce too much testosterone. These high insulin levels play havoc with the ovaries, causing follicles to develop.
PCOS can be treated to reduce the health risks by losing weight if needed, reducing testosterone and insulin levels through medication. For those inflicted with infertility, these efforts may be enough to restart a normal menstrual cycle. If not, ovulation-inducing medication can be given, and assisted reproductive methods such as IVF can be used in those still unable to conceive naturally.
 Grigorova M, Rull K and Laan M (2007) Haplotype Structure of FSHB, the Beta-Subunit Gene for Fertility-Associated Follicle-Stimulating Hormone: Possible Influence of Balancing Selection, Annals of Human Genetics, 71(1):18-28