One fifth of women aged between 35 and 45 have experienced difficulty conceiving, research has found.
Infertility - where a couple is unable to get pregnant despite having regular unprotected sex - is estimated to affect 3.5 million people in the UK.
A new study of more than 15,000 women and men in Britain discovered that one in eight women have experienced infertility, compared with one in 10 men.
However nearly half of them (42.7% and 46.8% respectively) didn't seek medical help for the issue.
Lead author Jessica Datta, from the London School of Hygiene and Tropical Medicine, said she was "surprised" by the findings.
For the study, which was published in the journal Human Reproduction, researchers analysed data from 15,162 women and men aged 16-74 who took part in Britain's National Survey of Sexual Attitudes and Lifestyles between 2010 and 2012.
They found that infertility affected women aged 35 to 45 the most as well as men aged between 35 and 55.
Infertility was most likely to be experienced by people who were married or living together at the time they were interviewed for the study.
This reflects the fact that those in stable relationships were more likely to attempt to have children and therefore become aware of fertility problems.
The study found that 42.7% of women and 46.8% of men didn't seek help for their infertility.
Those who did seek help were more likely to have a university degree or better paid jobs.
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"One of the important and concerning findings in our study is the difference in educational attainment and job status between people who sought help for infertility and those who did not," said Datta, according to Medical Xpress.
"Studies of infertility have tended to recruit research participants from medical settings such as general practice, so our population-based survey sample provides a rare insight into those people who, despite having failed to get pregnant after a year of trying, did not seek help from health services.
"The existence of inequalities in access to healthcare is well established but this is one of few analyses to explore uptake of services for infertility."
Researchers believe some people might not seek help because they do not understand or acknowledge that a problem exists. Additionally they may fear being labelled 'infertile' and might also have worries over the cost of treatment to help them conceive.
The study also found that women aged 50 or below who had experienced infertility were more likely to suffer from depression or feel dissatisfaction with their sex life than those who had not.
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"Previous research has found associations between undergoing treatment for infertility and sexual dissatisfaction," said Datta.
"In our study, symptoms of depression occurred in the two weeks before interview and sexual dissatisfaction in the year before interview but, as we don't know when the period of infertility occurred, we cannot make assumptions about causality and are in favour of further investigation into the long term impact of infertility on women's wellbeing."
Professor Geeta Nargund, medical director at CREATE Fertility, said: "This study emphasises the need for raising awareness about factors affecting female and male fertility from an early stage.
"It is well known that female fertility declines sharply after the age of 35. Age combined with lifestyle factors such as smoking, body weight, stress and medical and family history can also contribute to delay in conception.
"It is therefore important that women and men try to improve their fertility at all times."
She said there are free fertility open days held in some fertility units which help to educate couples about infertility and treatment options.
"I urge women and men to seek early help if they are having fertility problems in order to reduce the physical and emotional burden and cost of treatment," she continued.
"As a nation, we need to introduce a National Tariff for IVF on the NHS to achieve equal and fair access to treatment."
