A new study has found that women who want to have children later in life must conceive or freeze their eggs by the age of 35.

The research, done at the Hospital Unviersitari Quirón-Dexeus in Barcelona, Spain, headed by Dr Marta Devesa, is the largest and most detailed of its kind, as well as a response to the falling fertility on woman in subsequent years after 35.

Of all the women who have fertility treatment and go on to have a baby, about 24 percent of them are 38, according to the findings. A 38-year-old woman trying to conceive a child is 18 times more likely to do so than a woman only six years older.

The research team said there was a need for "more realistic expectations" among many women, who should either start trying for a family earlier, or else freeze their eggs, Telegraph reported.

If women who are about 30 decide to freeze their eggs, whether or not the intent to have kids is there or not, then it will be a lot easier down the road because they will have their own young eggs to use during the in-vitro fertilization process, instead of using the eggs of other donors, Gazette Review reported. 

The study aims to make women aware that their fertility crashes as they age and they should not be fooled by media stories about celebrities starting families in their 40s. 

"Women of 44 or older should be fully informed about their real chances of a live birth and counselled in favour of egg donation," Devesa told the European Society for Human Reproduction, according to The Guardian.