The optimum time for egg freezing is before a woman turns 35 as fertility declines with age. There is little point in women over 40 freezing their eggs, because the odds of a future pregnancy are very slim, announced UK fertility regulator the HFEA. So clinics must make it clear to women, reports BBC Health.
Yet data shows that the most common age at which women are treated is 38, with many freezing eggs into their 40s.
Women can only get egg freezing on the NHS if it is for medical reasons, such as needing a cancer treatment which may cause them later fertility problems. Private clinics also offer it to women who want it for social reasons, like delaying starting a family because they haven't met the right partner yet, BBC explains.
In 2016, 80% of the 1,310 freezing procedures carried out were done in private clinics, Around 890 of all the treatments were for women aged 35 and over, compared with 419 treatments for women younger than this.
The HFEA says women must be given clear information about the risks, costs and likely success rates of egg freezing, which is becoming an increasingly popular "fertility insurance" back-up plan.
Here are some egg freezing facts:
Egg freezing costs anywhere between £2,720 and £3,920 per go.
Birth rates from frozen own eggs are increasing but remain below that of conventional IVF treatment cycles, being successful one in every five times, on average, compared to around one in three for "fresh egg" IVF.
While a woman's age at thaw has relatively little impact on a woman's chances of success, the age at freeze does, with evidence suggesting that if eggs are frozen below the age of 35, the chances of success will be higher than the natural conception rate as the woman gets older, says the HFEA.
Aileen Feeney from Fertility Network said women should know their fertility "vital statistics" 28:35:42: "By 28, female fertility has already begun to fall; 35, female fertility plummets; 42, your chance of becoming a biological mother is vanishingly small."