A British fertility expert has clashed with a US specialist over when is the "right" time for single women who want children to resort to freezing their eggs.
Gillian Lockwood, medical director of Midland Fertility Services in Aldridge, near Birmingham, defended the practice despite US research showing that the average age of women seeking egg freezing for social reasons is between 37 and 39 - by which time their eggs are rapidly deteriorating.
A review of 26 studies to be presented at the annual meeting of the American Society for Reproductive Medicine (ASRM) in Orlando today has found that women who froze their eggs when they were under 30 had higher rates of success than those who were older.
Roger Lobo, president of the ASRM, warned women not to leave it too late.
Dr Lobo said egg freezing was still "an experimental procedure" with "insufficient evidence" to show whether it was a "worthwhile undertaking".
"Despite increasing numbers of clinics offering the procedure and the significant media attention paid to it in recent years, women are not pursuing elective egg freezing at an age when it would be most likely to help them accomplish their fertility goals."
But Dr Lockwood said although it was true that egg freezing was not an option for many women in their late 30s, "we have to ask what the comparator is here".
"The comparator is how well will these women do with their own eggs in their early 40s? A 39-year-old frozen egg is going to do better in IVF than a 42-year-old fresh egg, because the drop-off becomes so sharp during these years."
Dr Lockwood said she was frequently contacted by women in their mid to late 30s who were still single and wanted to freeze their eggs.
"They've discovered Mr Right has turned out to be Mr Wrong. They are deliberately and quite bravely trying to buy a bit of time."
Egg freezing is still rare in Britain but is recognised as a last resort for women who want to preserve their fertility, either because they have had cancer treatment or for social reasons.
Dr Lockwood has seen around 100 women in the last few years who want to freeze their eggs for social reasons.
"With most of the women I see we agree that social egg freezing is not appropriate, either because they've left it too late or because their ovarian reserve is too low.
"I see it as unethical if you are only going to get three or four eggs because really you need 16, 18, 20 to have a realistic chance of achieving pregnancy.
"I would still say a woman up to her mid-30s who wishes to be a genetic mother one day and has not met Mr Right would be much better freezing her eggs than hoping Mr Right turns up before she's 40."
* Scientists are developing a test that could dramatically boost IVF success rates from a single cycle of treatment. The technique, created at Oxford University, checks for chromosomal abnormalities in the developing embryo but also looks at two new markers that could potentially cause pregnancies to fail. Over time, researchers hope they can increase success rates towards the 100 per cent mark. At present, only around 30 per cent of IVF cycles worldwide result in a pregnancy, with many failing due to chromosomal abnormalities.