The number of women having IVF treatment in their forties has almost doubled in just seven years as more delay starting a family until their fertility has seriously declined, figures show.

The proportion of IVF patients aged between 40 and 45 has climbed sharply from about 10 per cent between 1991 and 1999 to more than 15 per cent last year, despite low success rates and a lack of NHS provision.

A total of 6,174 women in this age group had fertility treatment using their own eggs in 2006, compared with 3,296 in 1999 and just 596 in 1991, according to data published yesterday by the Human Fertilisation and Embryology Authority (HFEA). Several hundred more tried to conceive using donated eggs, though precise numbers are not available.

Fertility specialists said that the figures show how thousands of women are misjudging their biological clocks by waiting until their late thirties or beyond to try for a baby. When they fail to conceive, they turn to IVF at an age when their best chance of benefiting from it has already slipped away.

The average age of all fertility patients has also increased by a full year since 1996, from 33.8 to 34.8, reflecting the wider social trend towards later motherhood. The average age for first births rose from 26.5 in 1994 to 27.5 in 2004, and the average for married women has risen above 30.

The upward curve has alarmed doctors as IVF is rarely successful among the over40s and carries greater health risks both to women and any children they conceive.

“People need to realise that they cannot beat biology,” said Professor Bill Ledger, of the University of Sheffield. “The message is that if having children in your life is important to you, you should be trying by your mid30s or earlier. Women are thinking they can wait and, if they can’t get pregnant naturally, IVF will be able to help them.”

Clare Brown, chief executive of the patient charity Infertility Network UK, said: “A lot of people don’t realise the very real effect of age on fertility. They look at people like Cherie Blair having babies in their forties, and think they’ll be fine, or that IVF is there as back-up. I don’t think many people are aware of the very low success rates of IVF at that age.”

Between 40 and 42, the live birthrate for a first treatment cycle is 9 per cent, at 43 or 44 it is 3 per cent, and at 44 or above it is 1 per cent.

Fertility treatment also becomes more hazardous with advancing maternal age. At 40, the risk of miscarriage is twice what it is at 20, and there is an increased likelihood of ectopic pregnancy, premature birth, stillbirth, neonatal death and birth defects. Pregnancy complications are also more common, as are Caesarean sections.

The figures, which were released at the HFEA’s annual conference yesterday, do not reveal the social profile of women seeking IVF in their forties. Most, however, are likely to be well-off as the NHS pays for virtually no fertility treatment in this age group.

Angela McNab, the chief executive of the HFEA, said: “It may well be that one of the messages we need to concentrate on is reminding women about their biological clocks, and the increasing difficulties they will have having a baby after 40, and especially after 45.”

Sam Abdalla, a fertility specialist at the Lister Hospital in London said: “This is happening more for social reasons than for medical ones.”

Gillian Lockwood, of Midland Fertility Services said: “There are celebrities having children in their forties, of whom many are using donor eggs. That only serves to maintain this fiction that if a woman works out in a gym and uses Botox, then her ovaries are also going to have another decade in them.”

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