The trend to older motherhood is, however, unmistakable. The number of women giving birth in their 40s has risen more than 50 per cent in a decade, from 8,112 in 1987 to 12,309 in 1997.
While older motherhood brings greater health risks - to mother and baby - there are benefits. By the time they reach their late 30s or early 40s, women have a better chance of having established careers, financial security and a settled home life. They are less likely to feel resentment at opportunities missed because of restrictions that a new baby imposes.
Dr Julia Berryman, a psychologist at Leicester University who has researched older mothers for more than a decade, said: "Women who are adding to their families, as Cherie Blair is, tend to feel more relaxed than when they were younger and by far the majority say it is a good experience for them and their children."
Older mothers are more likely to breast-feed and their children do better on ability tests than those of younger mothers, probably because of the quality of child-parent interaction, Dr Berryman said. Younger mothers tend to be more punitive and are more likely to smack.
"On the whole, older mothers are more likely to maker a greater investment in their children while younger ones are more likely to feel resentment at what they have sacrificed," she said.
In the existing children, initial embarrassment at the evidence of what their parents have been up to usually turns to delight at the new addition to the family.
Older parents are less likely to compete with their children. This is especially evident in fathers and sons when the generation gap is wider and so both have a much more relaxed relationship.
On health grounds, there is no reason why a fit woman in her 40s should not have a successful pregnancy and birth. There is a greater risk of high blood pressure in the mother and of Down's syndrome in the child. The risk of Down's syndrome rises from one in 2,000 for a mother in her 20s to one in 22 for a mother of 45 but can be detected by screening.
Dr Berryman said: "In the 1980s the medical profession was very negative about older mothers. I think they have now recognised there isn't the evidence to support that view."Reuse content