The Big Question: So is there an optimum age for a woman to have a baby?

Why are we asking?

A major conference in the United States of fertility specialists heard this week two conflicting pieces of research.

One suggested women who become mothers over the age of 50 make just as good parents, and are just as psychologically well adjusted, as those in their forties and thirties.

The other suggested that delaying motherhood not only reduces a woman's chances of becoming pregnant - it may also reduce her daughter's chances. They are the latest contributions to one of the most emotive debates in the area of fertility and its treatment: the best age for motherhood.

Why is age such an issue now?

Because the age of motherhood is rising. Half of all births are to mothers over 30 compared with just over a quarter (27 per cent) 20 years ago.

Over-35s account for 9 per cent of all births, more than twice the figure 20 years ago. The pregnancy rate in women over 40 is rising faster than in any other age group. Almost 25,000 women now become mothers each year in their fourth decade.

Women are either delaying childbirth while they develop their careers or while they search for the right man to be the father.

What is wrong with that?

Quite a lot, according to fertility specialists. The modern woman who delays starting a family into her thirties is defying nature and risking heartbreak, they say. Women who try to "have it all" may lose the one thing that matters most, the opportunity to have a family.

The "biologically optimal" time for childbearing is 20 to 35. Beyond 35, the risks to the health of mother and baby including high blood pressure, diabetes and foetal abnormality rise. As the average age of motherhood has risen, so has the rate of complications and abnormalities.

Obstetricians have warned that the "bio-panic" women used to suffer on their 30th birthday has moved up to the 40th and have suggested that instead of waiting for Mr Right they maybe ought to wait for Mr Good Enough if they want a family. Some experts have predicted that a fertility time bomb hangs over Britain over the next decade as women delay childbearing. One in seven couples has problems conceiving and this could rise to as many as one in three if present trends continue.

Isn't there the option of IVF if all else fails?

Many couples believe this - wrongly. Fertility treatment is expensive, invasive and has a high failure rate. Seven out of 10 women who have in vitro fertilisation (IVF) do not achieve a live birth and this rises to nine out of ten for the over 40s, though success rates are improving. NHS provision is patchy and scarce and unavailable to women over 39.

The British Fertility Society issued a stark warning to women last year not to delay trying for children in the belief that they could fall back on IVF if all else failed. Despite this, the number of older women giving birth is likely to surge over the next decade as demand rises and techniques improve.

Only 24 women over 50 had children through IVF in 2002, the last year for which figures are available.

How will new techniques help older women?

Egg freezing will revolutionise IVF by allowing women to store "young" eggs of high quality in their 20s and 30s for use later. The biological age of the egg is important for the success of IVF and the health of the resulting baby, although it will not reduce the health risks of pregnancy and labour to the mother.

The first baby conceived using a frozen egg was born in 1986 and only about 300 have been born worldwide since. So far the technique has been mostly limited to cancer patients. But some women have already had treatment for social reasons. Expertise with the technique has advanced most rapidly in Italy.

What about the psychological consequences?

Rearing children is demanding and the question of whether older mothers will be able to cope is a concern. The small study of older mothers presented to the American Society of Reproductive Medicine meeting in New Orleans this week by researchers from the University of Southern California suggested they were doing just as well as younger mothers. But the oldest child in the study was 12, prompting British specialists to ask how the mothers will cope in their sixties and seventies when their children are teenagers.

There are obvious advantages of being older: greater maturity and financial security among them. Children of older parents tend to do better at school but this could be because older parents tend to be better off and better educated.

On the downside, the older the parents the greater the risk that the children will suffer early bereavement.

What about older fathers?

Double standards are plain in our divergent attitudes to men and women who come late to parenthood.

"What a trouper" the headlines proclaimed when the entertainer Des O'Connor said he was to be a father at 72. The birth of Gordon Brown's children in his fifties have similarly been seen as an occasion for celebration. Not so Patricia Rashbrook, Britain's oldest mother who gave birth in July after IVF treatment abroad at the age of 62. She was accused of being selfish and placing her own needs above the needs of her child.

Older mothers make us uneasy - in part because of the increased risks. But these are not confined to women. Research published earlier this year suggested that men over 40 were six times more likely to father a child with autism than their younger peers.

The risk of autism rose steadily with advancing paternal age but there was no link with increasing maternal age, the study published in Archives of General Psychiatry said.

The finding suggests that men may have their own biological clock which affects their capacity to produce healthy offspring as they age.

Is age any longer a barrier to motherhood?

Yes...

* The biologically optimal time, when the chances are highest and the risks lowest, is 20 to 35

* One in seven couples is infertile and this will rise if the trend to later motherhood continues

* IVF is expensive and has a high failure rate and it is a mistake for couples to think they can rely on it

No...

* The physical factors surrounding pregnancy have to balanced with the emotional and psychological factors

* Older mothers may face higher risks but be more mature and more financially secure

* Only the woman and her partner can decide what is the best time to have a baby, having weighed up all the risks