The Royal College of Obstetricians and Gynaecologists is to publish evidence on Monday about the increased medical risks of pregnancy for older mothers.
While most pregnancies in the UK result in a healthy baby, experts say a minority of older women face the risk of serious adverse effects such as developing diabetes in pregnancy.
AdvertisementMandish Dhanjal, a consultant obstetrician who has pulled together the evidence on medical risks for the college, said that the trend to older motherhood was very marked.
"If you look at older mothers over the age of 35 - in the mid 1980s about 8% of those women who got pregnant were over 40 whereas now that figure has more than doubled to 19%."
The risks for a woman in her 40s of medical complications are between two and five times higher than a woman in her 20s, although the absolute risks are still quite small.
Two of the most serious risks highlighted by the college are pre-eclampsia and diabetes.
There is also a concern among specialists that women's perception of motherhood may be overly influenced by celebrity older mothers.
"Many young women will be reading magazines which focus on this. Unfortunately the mass media doesn't tend to report the complications," Mr.Dhanjal told Branwen Jeffreys, BBC's Health correspondent, BBC News
They are concerned many women still do not understand how rapidly fertility declines after the age of 35.
For a woman over the age of 42 the success rate of a live birth for each IVF cycle falls to 5%, whereas for a woman under 35 it is 31%.
But some seem to think that there is a very good health system that is able to minimise the risks for women having children at 35 or 36.
Mary Newburn, of the National Childbirth Trust, said while the parenting charity supported the efforts to make women aware of the medical risks, changes to working practices were also needed.
"We now need to look at how we can make it possible for women to have career breaks earlier on and to enable them to have children at a younger age.
"Likewise, the introduction of shared parental leave should lead to less pressure on women to reach a certain point in their career before having children."