Women who continue having children late in life may live longer than those who have their kids young, research finds.
The secret of a longer life?
A team at Finland's University of Turku suggests women who raise a family late in life tend to die later.
Writing in Proceedings of the Royal Society, the researchers admit they were surprised by the findings.
It has long been thought women who have children late are less well-equipped to survive the traumas of childbirth and raising a young family.
But the latest study suggests that, in certain populations, having babies later in life may be a sign of physical robustness.
Scientists believe the findings suggest the rate at which a woman's reproductive system ages is directly linked to the speed with which the rest of her body ages.
"This result is unexpected because late age at reproduction is not generally believed to be favoured by natural selection, owing to its adverse effects on both the survival of the mother and the offspring, " they said.
However, the result fits with earlier studies that showed the later a woman goes through the menopause, the longer she is likely to live.
Figures show the average age at which women in Britain give birth is now 30.
The Prime Minister's wife Cherie Blair was 45 when she had her fourth child Leo in 2000.
The Finnish researchers studied a population of people, called Sami, who lived in northern Scandinavia from the 17th to the 19th centuries.
They chose this group because they lived in isolated regions and had little advanced medical care, which meant they experienced what researchers called 'natural mortality'.
They focused on women and the age at which they had had their children. Centuries of data revealed having children young, or having lots of them, made little difference to how long the mothers lived.
But the age at which they stopped childrearing was significant.
Researcher Dr Samuli Helle told the BBC News website it might be possible that the physiology underlying both reproductive and general physical decline was in some way linked.
Therefore the ability to have children until relatively late in life might be a sign that a woman is well equipped to live to an advanced age.
A spokeswoman for the Family Planning Association said modern older mothers tend to plan their pregnancies so that they are financially and psychologically ready to have a family.
This could reduce the effects of stress on the ageing process.
"Many women are now making a lifestyle choice by putting their education or career first and then saying 'right, I have achieved that, now I want a family'.
"Giving women power and control over their own fertility is in itself a good thing."