These days, many women are hoping to have children later in life, but this brings with it the looming pressure of waning fertility once you hit 31. While some women have no trouble conceiving well into their late 30s and early 40s, others have to seek out alternatives such as IVF, and even then, they can experience varying levels of success.

So researchers at the Centre for Human Reproduction in New York have designed a new fertility test to help young women better plan their pregnancies. Called 'What's My Fertility', the test can be taken between the ages of 18 and 35, and can identify women who are at high risk of low fertility later in life, giving them the chance to freeze their eggs for use in IVF later on.

"After treating infertility in women for decades and hearing them tell us time and time again that they wished they had known of the risk of premature ovarian ageing (POA) so that they could have planned for a family sooner, we were determined to find a better way to proactively identify POA in young women," Norbert Gleicher, medical director and chief scientist at the Centre for Human Reproduction told Sarah Knapton at The Telegraph.

While men produce new reserves of sperm throughout their lives, woman get all the eggs they're ever going to produce on the day they're born. But this doesn't mean every egg is a viable one. The capacity for a woman's ovaries to produce high-quality eggs is known as ovarian reserve (OR), and with age, a woman's OR naturally declines. 

This is why in the average population of women 30 years and younger, there will be about 400 pregnancies for every 1,000 women (40 percent) not using contraception for one calendar year, Nick Raine-Fenning from the University of Nottingham in the UK writes for The Conversation.  

"It then begins to decrease until around the age of 45, when only 100 women will conceive for every 1,000 (10 percent) not using contraception," he says. "Miscarriage rates also steadily increase. About 10 percent of women will miscarry at the age of 20, compared to 90 percent or more at 45 years of age or older."

In approximately 10 percent of women, this natural decrease in ovarian function is accelerated, and can leave them with far fewer eggs than they should as they grow older. Women living with premature ovarian ageing (POA) can find it difficult - if not impossible - to fall pregnant on their own and also through fertility treatments if left too late, which is why it's so important for them to be diagnosed as early as possible. 

"Screening will empower women with the knowledge they need to make informed decisions earlier in life and will help them avoid the emotional and hefty costs of later infertility treatments," Gleicher told The Telegraph. "Rather than diagnosing women when they already suffer from this condition, What's My Fertility identifies women who are at risk, so they can prevent this condition from affecting their family plans."

The test costs £65 ($US98) and works by analysing hormonal changes in the patient's blood while seeking out a specific genetic variation that's been associated with higher POA risk. The patient is required to answer an online questionnaire about her family history and lifestyle, and undergo three blood tests. "Two look for high levels of follicle stimulating hormone (FSH) and low levels of anti-Müllerian hormone (AMH) which show that fewer eggs are present," Knapton reports. "The third test checks for a mutation to the FMR1 gene."

So far, the test is only available to women in Britain, but if it proves successful, similar tests will likely be made available elsewhere in the world. 

That said, experts are warning that What's My Fertility should not be considered the final word on an individual woman's fertility status. Charles Kingsland from Liverpool Women's NHS Foundation told The Telegraph that while tests like this can be useful, the results should be taken when a grain of salt, as hormonal levels can sometimes be an inaccurate indication of what's really going on. For example, they could tell you how many eggs you've got left, but not how many healthy, viable eggs you've got.

So if you do choose to have this test or something similar done, remember - as with everything important to do with your body, you should always get a second opinion before making any life-changing decisions.